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we develop an ultra-stable mid-ir array for the observation of exoplanet transits.this spectrometer is needed to achieve the required sensitivity for the detection of atmospheric bio-signatures in habitable-zone planets around m-dwarfs. | an ultra-stable mid-infrared sensor for the detection of bio-signatures by means of transit spectroscopy |
ultraviolet (uv) astronomy is a very demanded branch of astrophysics. many short-term uv experiments in space as well as long-term observatories in last decades have brought fundamental data for the understanding of the physics of the universe. in this article, we briefly describe the current status of the uv domain role to be played by the world space observatory - ultraviolet (wso-uv). the wso-uv was described in previous publications in great detail, therefore only basic information and current state of the project are briefly presented in this paper. a brief overview of major science topics that have been included in the core program of the wso-uv is presented; exoplanetary studies form a considerable part of the core program. wso-uv observations will allow the direct determinations of atomic oxygen content and of the presence of ozone, which will provide breakthrough data for exploring the possibility of life on exoplanets. | prospects of wso-uv mission for studies of exoplanetary atmospheres. |
the recent detection of a candidate exoplanet at the stellar rotation period of the young m dwarf ad leo places a new emphasis on understanding the persistence and chromaticity of starspot signals for the lowest-mass stars. we have obtained highly precise multi-wavelength doppler spectroscopy of four rapidly-rotating m dwarfs using the near-infrared habitable-zone planet finder on mcdonald observatory's 10m hobby-eberly telescope, and the optical hires spectrometer on the 10 keck i telescope. our doppler observations are complemented by photometry from kepler, tess, and the las cumbres observatory (lco) network of telescopes. for all four targets, we recover strong rv signals at the stellar rotation period. some of these signals remain coherent for hundreds of stellar rotations, which bears important implications for detecting exoplanets around similar objects. we will discuss the persistence, chromaticity, and relation to photometry of each. | exploring persistent doppler signals in rapidly-rotating m dwarfs |
the discovery and characterisation of new extra-solar planets (exoplanets) is ongoing, but to date only a handful of low-mass planets have been found orbiting in the habitable zone of sun-like stars. the next generation of major facilities (e.g. tess and plato) aimed at the systematic search for earth-like planets orbiting solar-like stars will be operational in the coming years, and some of the planets they will find may orbit stars close enough for atmospheric characterisation, including the possible detection of bio-signature gases. studies on the formation and evolution of the earth reveal that an earth-like habitat is characterised by a n-dominated atmosphere and could be detected by measuring the relative atmospheric abundances of n, o, c, and h (noch). however, n, which is the main fingerprint of an earth-like habitat, is extremely difficult to detect and may be possible only in the ultraviolet, a wavelength range that has not been studied for low-mass exoplanets. before starting the search for bio-signatures with future facilities (e.g. elts, luvoir), we need to explore our capabilities to detect earth-like habitats. here, we present several synthetic transmission spectra for the earth's atmosphere, for the wavelength range 915 to 11000 å, at a spectral resolution of r = 100,000. we focus on both atomic and molecular features, and discuss the detectability of n. | teth - towards extra-terrestrial habitats |
tides can strongly affect the evolution of the spin of planets. super-earths presenting a solid core and an atmosphere are submitted to both gravitational tides caused by bodies’ mutual gravitational interactions and thermal tides resulting from stellar insolation. thermal tides are particularly important for planets in the habitable zone where they drive the tidal response of the atmosphere (correia & laskar 2008). they play a key role for the equilibrium states of the spin, as in the case of venus (correia & laskar 2004) and of exoplanets (e.g. the numerical simulations by leconte & al. 2015). given the complex mechanisms involved in thermal tides, analytic models are essential to understand the dependence of the perturbation on the physics on the atmosphere and the tidal frequency. the one proposed in the 60’s by lindzen and chapman explains well thermal tides in the asymptotic regime of fast rotators but presents a singularity near synchronization. we will present a new analytic approach that generalizes these early works to all regimes of tidal perturbations. this model describes the mechanisms of tidal waves generated in the atmosphere by both gravitational and thermal tides. the tidal torque is computed as a function of the frequency of the forcing and agrees very well with results obtained by direct numerical simulations using general circulation models. | towards a new model of atmospheric tides: from venus to super-earths |
venus is a planet of critical importance in the study of terrestrial atmospheres and the evolution of habitable surface environments. we describe how venus data is being used to characterize exoplanets and define the limits of the habitable zone. | venus as a laboratory for exoplanetary science |
the past several decades have seen an explosion in humanity's knowledge about the existence of distant worlds. thousands of exoplanets have been now been discovered thanks to the development and refinement of the radial velocity (rv) and transit techniques. we are beginning to piece together an understanding of the diversity of these worlds and of the mechanisms that drive planet formation and evolution. while this progress has been titanic, earth-sized planets in the habitable zones of sun-like stars (the places most suited to host life as we know it) remain out of our reach. noise created by stellar activity along with insufficient instrumental precision conspire to obscure the minuscule signals created by these putative worlds. in this thesis, i chart a course from the discovery of giant exoplanets, to the novel applications of statistical techniques and improved instrumentation, which together show promise of allowing us to finally detect true earth analogs. in chapter 2, i present the discovery and confirmation of a pair of transiting hot jupiters, both identified as planet candidates by the tess space telescope. our team collected ground-based photometry, conducted high-contrast imaging, and performed doppler spectroscopy with chiron to verify the planetary nature of both candidates. toi 564 b is nearly 50% more massive than jupiter and orbits its star in about 1.7 days. it exhibits a rare grazing transit, making its planetary radius difficult to ascertain. toi 905 b is slightly larger than jupiter but only about two thirds its mass, and it orbits its host star in about 3.7 days. both targets are good candidates for follow-up characterization. in particular, as the one of the brightest known stars to host a grazing transiting planet, toi 564 is a prime target for future observations that could leverage its planet's transit geometry to constrain the presence of additional planets in the system. in chapter 3, i present a novel application of principal component analysis (pca) to the problem of stellar activity. as rv precision has improved, astronomers are now having to contend with astrophysical noise sources that contaminate rv observations. photospheric features such as spots and faculae create time-varying sources of rv noise that collectively dwarf the rv signals induced by small (earth-like) exoplanets. overcoming this noise source is a high priority for the astronomical community because it would enable the detection of potentially habitable planets around bright nearby stars. when pca is applied to realistic simulated time-series spectra, the fingerprints of stellar activity are revealed. stellar activity manifests itself throughout stellar spectra on a pixel-by-pixel basis. my simulations show that the signatures of stellar activity are better recovered with high resolution than with high signal-to-noise ratios, even after the spectral lines are fully resolved. this prediction has contributed to the design of future planet-hunting spectrographs. finally, in chapter 4, i introduce a new spectrograph designed and built by the yale exoplanet lab, the extreme precision spectrograph (expres). i compare expres's performance to that of its predecessor, chiron, by focusing on two well-studied stars: tau ceti (a chromospherically quiet star) and epsilon eridani (a chromospherically active star). expres outperformed chiron in terms of its single-measurement rv precision for both targets by a factor of 3. expres's improvement factor over chiron was smaller, however, when considering the root-mean square velocity error. i conducted a periodogram analysis and a collection of planet injection and recovery simulations to further measure the relative performance of these instruments. the results suggest that expres is delivering exquisite instrumental precision, but that addressing the impact of stellar activity remains essential to reach truly extreme on-sky precision for real stars. the future course of exoplanet science hinges upon whether it is possible to identify numerous nearby potentially habitable planets. the rv technique, already enormously successful at identifying and characterizing large planets, requires significant improvement in order to overcome the daunting challenge of noise produced by stellar activity. taken together, recent innovations in the design of new high-precision spectrographs along with the burgeoning community-wide interest in the use of statistical techniques to decorrelate stellar activity rvs from planetary rvs, afford many reasons to be optimistic about the future of exoplanetary science and about the search for life beyond the solar system. | wobbling towards the future: applications of the radial velocity technique to detect ever-smaller exoplanets |
wide binary star systems with circumstellar exoplanets are generally believed to be conducive to habitable planets. we demonstrate that in the presence of a giant planet secular perturbations can affect the habitable zone for a wide range of system parameters. such perturbations lead to enhanced eccentricities of terrestrial planets and are detrimental to sustain habitable conditions on the planet. we develop a diagnostic tool based on analytical models that allows an easy identification of observed binary systems lacking habitable conditions from a dynamical point of view. | dynamical limitations on the habitability of planets in binary star systems |
the first challenge in the hunt for life elsewhere in our universe is to decide where to look. in a new study, two scientists examine whether sun-like stars or low-mass m dwarfs are the best bet for hosting exoplanets with detectable life.ambiguity of habitabilitythe habitable zones of cool m-dwarf stars lie much closer in than for sun-like stars, placing habitable-zone planets around m dwarfs at greater risk of being affected by space weather.most exoplanet scientists will freely admit frustration with the term habitability its a word that has many different meanings and is easily misinterpreted when it appears in news articles. just because a planet lies in a stars habitable zone, for instance, doesnt mean its necessarily capable of supporting life.this ambiguity, argue authors manasvi lingam and abraham loeb (harvard university and harvard-smithsonian center for astrophysics), requires us to take a strategic approach when pursuing the search for primitive life outside of our solar system. in particular, we risk losing the enthusiasm and support of the public (and funding sources!) when wefocus on the general search for planets in stellar habitable zones, rather than specifically searching for the planets most likely to have detectable signatures of life.illustration of the difference between a sun-like star and a lower-mass, cooler m-dwarf star. [nasas goddard space flight center/s. wiessinger]weighing two targetsso how do we determine where best to look for planets with detectable biosignatures? to figure out which stars make the optimal targets, lingam and loeb suggest an approach based on standard cost-benefit analyses common in economics. here, whats being balanced is the cost of an exoplanet survey mission against the benefit of different types of stellar targets.in particular, lingam and loeb weigh the benefit of targeting solar-type stars against that of targeting stars of any other mass (such as low-mass m-dwarfs, popular targets of many current exoplanet surveys). the advantage of one type of target over the other depends on two chief factors:the probability that the targeted star hosts planets with life, andthe probability that biosignatures arising from this life are detectable, given our available technology.promise of sun-like starsrelative benefit of searching for signatures of life around stars with varying masses, assuming a transmission spectroscopy survey mission; results are similar for a direct-imaging mission. green curve assumes a flat prior; red and blue curves assume priors in which habitability is suppressed around low-mass stars. [lingam loeb 2018]taking observational constraints into account, lingam and loebs results depend on what is known in statistics as a prior an assumption that goes into the calculation. the two possible outcomes are:if we assume a flat prior i.e., that the probability of life is the same for any choice of star then searching for life around m-dwarfs proves the most advantageous, because the detection of biosignatures becomes much easier.if we assume a prior in which habitability is suppressed around low-mass stars, then it is more advantageous to search for life around solar-type stars.so which of these priors is correct? there is mounting evidence, particularly based on considerations of space weather, that the habitability of earth-like planets around m dwarfs might be much lower than their counterparts around solar-like stars.if this turns out to be true, then lingam and loeb argue exoplanet survey missions should target sun-like stars throughout our galaxy for the best chances of efficiently detecting life beyond our solar system.citationmanasvi lingam and abraham loeb 2018 apjl 857 l17. doi:10.3847/2041-8213/aabd86 | where should we look for life? |
we explore the feasibility and potential characteristics of photosynthetic light-harvesting on exo-planets orbiting in the habitable zone of low mass stars ($< 1$ m$_{\odot}$). as stellar temperature, $t_{s}$, decreases, the irradiance maximum red-shifts out of the $400 \textrm{nm} \leq \lambda < 750$ nm range of wavelengths that can be utilized by \emph{oxygenic} photosynthesis on earth. however, limited irradiance in this region does not preclude oxygenic photosynthesis and earth's plants, algae and cyanobacteria all possess very efficient \emph{light-harvesting antennae} that facilitate photosynthesis in very low light. here we construct general models of photosynthetic light-harvesting structures to determine how an oxygenic photosystem would perform in different irradiant spectral fluxes. we illustrate that the process of light-harvesting, capturing energy over a large antenna and concentrating it into a small \emph{reaction centre}, must overcome a fundamental \emph{entropic barrier}. we show that a plant-like antenna cannot be adapted to the light from stars of $t_{s}<3400$ k, as increasing antenna size offers diminishing returns on light-harvesting. this can be overcome if one introduces a slight \emph{enthalpic gradient}, to the antenna. interestingly, this strategy appears to have been adopted by earth's oxygenic cyanobacteria, and we conclude that \emph{bacterial} oxygenic photosynthesis is feasible around even the lowest mass m-dwarf stars. | thermodynamic limits on oxygenic photosynthesis around m-dwarf stars: generalized models and strategies for optimization |
the apogee-koi program (fleming+ 2015aj....149..143f) used the northern apache point observatory (apo) galactic evolution experiment (apogee) spectrograph (apogee-n) located on the sloan 2.5m telescope at apo. apogee-n is a multiobject, fiber-fed, near-infrared spectrograph capable of observing up to 300 objects simultaneously at high resolution (r~22500) in the h band (1.514-1.696um). the field of view (fov) for apogee-n has a radius of 1.49°, which coincidentally provides an opportunity to use the multiplexing capabilities of apogee-n and simultaneously observe multiple kois from one kepler ccd module. the apogee-koi program began in 2013 under sdss-iii and completed observations in 2020 as part of sdss-iv. it targeted ~1600 kois for a median of 19 epochs per target and a median baseline of 683 days (1.87yr). the targets for the apogee-koi program include confirmed planets, planetary candidates, and false-positive systems. figure 1 displays the observed kepler footprint along with the targets observed with apogee-n. table 1 provides a list of the stars, including non-kois, observed as part of the apogee-koi program. see section 2. in this paper, we present an analysis of a subset of the apogee-koi program: the 28 kois listed in table 2. kepler observed our targets for the entirety of the original mission in long-cadence mode (30-minute cadence) with data from 2009 may 13 through 2013 may 11. some targets were observed in short-cadence (2-minute cadence) mode. see section 3.1. a total of 23 kois (see table 3) were observed as part of the robo-ao kepler planetary candidate survey (law+ 2014, j/apj/791/35 ; baranec+ 2016, j/aj/152/18 & ziegler+ 2017, j/aj/153/66 and 2018, j/aj/155/161). these observations were performed using the robo-ao laser adaptive optics system on the 2.1m telescope at kitt peak national observatory with a 1.85m circular aperture mask on the primary mirror. see section 3.2. in this work, we do not use archival apogee dr17 rvs but instead derive rvs using the processed dr17 spectra. see section 3.3. koi-129, koi-219, koi-415, koi-466, koi-855, and koi-1288 were observed with the sophie spectrograph as part of observations of the kepler field. sophie (wavelength coverage of 3872-6943å) is located on the 1.93m telescope at the observatoire de haute-provence. the observations for these targets were acquired between 2013 june and 2018 september and were obtained using an exposure time of 1800s in high-efficiency mode, which provides a resolution of r~40000. see section 3.4. koi-631 was observed with the habitable-zone planet finder (hpf) spectrograph between 2019 march 3 and 2019 july 17. hpf is a high-resolution (r~55000), fiber-fed, temperature-controlled, near-infrared (λ~8080-12780å) spectrograph located on the 10m hobby-eberly telescope (het) at mcdonald observatory in texas. see section 3.5. (5 data files). | vizier online data catalog: low-mass companions to kois observed with apogee (canas+, 2023) |
continuing improvements in both instruments and analysis techniques for determining stellar radial velocities are enabling the search for exoplanets below the 1 m/s level. amongst improvements required to reach the 10 cm/s level, necessary for detecting earth-mass planets in the habitable zone of sun-like stars, is better characterization and control of spectrograph variability beyond wavelength calibration. this includes the spectrograph response function (or instrument profile) which varies both as a function of wavelength across the spectrograph and also as a function of time. i will present observations of the instrument profile of the harps-n spectrograph using an astro-comb, a laser frequency comb optimized for spectrograph calibration. we observe instrument profiles with long, asymmetric tails with substantial structure which affect the centroids of calibration and stellar spectral lines, and thus the observed radial velocity. evidence for the temporal variability of the line profile from the harps-n/tng solar telescope will also be presented. techniques for mitigation of these issues to enable improved spectrograph rv stability will be discussed. | characterizing instrument profiles of high-resolution spectrographs with a laser frequency comb |
perhaps the simplest question that one can ask of a distant star or planet is, "what does it actually look like?" even the best interferometers can only image the surfaces of select giant and/or nearby stars, while the direct imaging of exoplanet surfaces is all but impossible. fortunately, several techniques exist that allow us to indirectly infer what the surfaces of stars and exoplanets look like from precise photometric light curves and high resolution spectral timeseries. in this talk, i will touch on the mathematical theory behind the mapping problem, including its degeneracies and limitations. i will discuss novel approaches to producing surface maps of stars and exoplanets using the recently developed starry code (https://github.com/rodluger/starry), with the goals of (1) understanding the statistical properties of spots and other surface features on low mass stars as a function of spectral type, (2) producing low resolution maps of close-in exoplanets from phase curves and secondary eclipses, and (3) one day applying these techniques to produce maps of terrestrial planets in the habitable zones of their stars to identify potential oceans and continents. i will focus in particular on two methods that maximize the fisher information of the mapping problem: light curves observed in reflected light and doppler imaging based on multi-epoch high-resolution spectra. by decomposing surface maps into spherical harmonics, i will show how both problems can be tackled analytically, allowing one to not only find the maximum likelihood solution quickly, but also the full posterior over maps. i will discuss ongoing work to apply these methods to the mapping of stars and exoplanets with current and upcoming instrumentation. | surface maps of stars and exoplanets |
the segmented pupil experiment for exoplanet detection (speed) facility aims to improve knowledge and insight into various areas required for gearing up high-contrast imaging instruments adapted to the unprecedented high angular resolution and complexity of the forthcoming extremely large telescopes (elts). speed combines an elt simulator, cophasing optics, wavefront control and shaping with a multi-deformable mirror (dm) system, and optimized small inner-working angle (iwa) coronagraphy. the fundamental objective of the speed setup is to demonstrate deep contrast into a dark hole optimized for small field of view and very small iwa, adapted to the hunt of exoplanets in the habitable zone around late-type stars. speed is designed to implement an optimized small iwa coronagraph: the phase-induced amplitude apodization complex mask coronagraph (piaacmc). the piaacmc consists in a multi-zone phase-shifting focal plane mask (fpm) and two apodization mirrors (piaa-m1 and piaa-m2), with strong manufacturing specifications. recently, a first-generation prototype of a piaacmc optimized for the speed facility has been designed and manufactured. the manufacturing components exhibit high optical quality that meets specifications. in this paper, we present how these components have been characterized by a metrological instrument, an interferential microscope, and then we show what is yielded from this characterization for the fpm and the mirrors. eventually, we discuss the results and the perspectives of the implementation of the piaacmc components on the speed setup. | a metrological characterization of the speed test-bed piaacmc components |
m dwarf stars are smaller and cooler than our sun. exoplanets transiting nearby m dwarfs produce very precise transit light curves due to their large planet-to-star radius ratios (rp/r*). the nearby m dwarf lhs 1140 (15 parsecs away and 0.2 solar radii) has two transiting super-earths, lhs1140b and lhs1140c (dittmann et al. 2017; ment et al 2018). due to only a few published transits of both planets, follow-up observations are required in order to update their parameters and find possible hidden planets or moons. using photometric observations from the 3.5m telescope at the apache point observatory and 1m telescopes at las cumbres observatory, we captured two transits for lhs1140b and four for lhs1140c. we updated the mid-transit times, period, rp/r*, inclination and semi-major axes for both planets. we found lhs1140c to be at an orbital distance of 0.024 au and lhs1140b at 0.094 au. at that distance, with a maximum equilibrium temperature of 230 k, we can confirm that lhs1140b is in its star's habitable zone. as there is still much discussion on whether or not a planet can keep its atmosphere in the habitable zone of an m dwarf star, lhs 1140b is a prime target for atmospheric studies. using the transits we observed plus the ones published by dittmann et al. (2017) and ment et al. (2018) we looked for transit timing variations and transit duration variations, and found none for either planet. the distance and size of lhs 1140 make lhs 1140b and lhs 1140c prime candidates for atmospheric characterization with jwst. both planets likely formed around the same time in different temperature regimes. these sister planets can therefore offer some insight as to how planets evolve as a function of distance from their host star. | photometry of the super-earths transiting the nearby m dwarf star lhs1140 |
methane (ch4) is a primarily biogenic greenhouse gas. as such, it represents an essential biosignature to search for life on exoplanets. atmospheric ch4 abundance on earth-like inhabited exoplanets is likely controlled by marine biogenic production and atmospheric photochemical consumption. such interactions have been previously examined for the case of the early earth where primitive marine ecosystems supplied ch4 to the atmosphere, showing that the atmospheric ch4 response to biogenic ch4 flux variations is nonlinear, a critical property when assessing ch4 reliability as a biosignature. however, the contributions of atmospheric photochemistry, metabolic reactions, or solar irradiance to this nonlinear response are not well understood. using an atmospheric photochemical model and a marine microbial ecosystem model, we show that production of hydroxyl radicals from water vapor photodissociation is a critical factor controlling the atmospheric ch4 abundance. consequently, atmospheric ch4 partial pressure (pch4) on inhabited earth-like exoplanets orbiting sun-like stars (f-, g-, and k-type stars) would be controlled primarily by stellar irradiance. specifically, irradiance at wavelengths of approximately 200-210 nm is a major controlling factor for atmospheric pch4 when the carbon dioxide partial pressure is sufficiently high to absorb most stellar irradiance at 170-200 nm. finally, we also demonstrated that inhabited exoplanets orbiting near the outer edge of k-type stars' habitable zones are better suited for atmospheric pch4 buildup. such properties will valuably support future detection of life signatures. | controls of atmospheric methane on early earth and inhabited earth-like terrestrial exoplanets |
at present, detecting new rocky planets within the habitable zone and the radial velocity follow-up of transiting candidates are priority objectives of the exoplanetary field. both, require a great effort including high-precision instruments and state-of-the-art analysis techniques. additionally, a proper observing strategy is crucial to ensure the effectiveness of the observations, avoiding unnecessary measurements that waste invaluable telescope time. in this talk, we present the kobesim algorithm, a bayesian-based strategy for the detection of planets in radial velocity surveys. it is developed within the kobe experiment, aspiring at maximizing the detection of potential habitable exoplanets orbiting late k-dwarfs. the algorithm uses the first data obtained for a given star to choose a target orbital period (usually the highest power periodicity) and uses bayesian inference to propose the optimum next observing date, thus accelerating the detection/rejection of such period. this new approach has demonstrated to improve the detection efficiency in comparison with a conventional strategy of monotonic cadence, reaching a detection in $\sim$50% less observations and timespan. kobesim has the potential to save expensive telescope time in current and upcoming instruments, and to allow the detection of light planets further away from their host star in reasonable timespans. | the kobe experiment - kobesim: improving rv detection through efficient scheduling |
kepler-62f is the first exoplanet small enough to plausibly have a rocky composition orbiting within the habitable zone (hz) discovered by the kepler mission. the planet is 1.4 times the size of the earth and has an orbital period of 267 days. at the time of its discovery, it had the longest period of any small planet in the habitable zone of a multi-planet system. because of its long period, only four transits were observed during kepler's interval of observations. it was initially missed by the kepler pipeline, but the first three transits were identified by an independent search by eric agol, and it was identified as a planet candidate in subsequent kepler catalogs. however in the latest catalog of exoplanets (thompson et al., 2018), it is labeled as a false positive. recent exoplanet catalogues have evolved from subjective classification to automatic classifications of planet candidates by algorithms (such as `robovetter'). while exceptionally useful for producing a uniform catalogue, these algorithms sometimes misclassify planet candidates as a false positive, as is the case of kepler-62f. in particularly valuable cases, i.e., when a small planet has been found orbiting in the habitable zone (hz), it is important to conduct comprehensive analyses of the data and classification protocols to provide the best estimate of the true status of the detection. in this paper we conduct such analyses and show that kepler-62f is a true planet and not a false positive. the table of stellar and planet properties has been updated based on gaia results. | kepler-62f: kepler's first small planet in the habitable zone, but is it real? |
terrestrial exoplanets in the habitable zones of nearby m dwarfs represent the first targets for the search for life outside of the solar system. it has been long thought that one of the most obvious biosignatures on alien worlds would be the spectroscopic detection of o2 and/or o3, created by a global biosphere of photosynthetic life forms (meadows et al., 2018). however, modeling has suggested that large amounts of o2 can be created abiotically—especially on terrestrial planets around m dwarfs. in particular, gao et al. (2015) showed that desiccated worlds with co2-rich atmospheres can build up 15% o2 via co2 photolysis. venus, nonetheless, has little atmospheric o2, despite ongoing co2 photolysis. this has been attributed to catalytic cycles involving clox and sox that regenerate co2 from co and o (mills et al., 2007; yung & demore, 1999). we seek to ascertain how these cycles behave on venus-like planets around different types of stars. we have constructed a 1-d photochemical model based on zhang et al. (2012) to study the atmospheric chemistry of venus-like exoplanets. the model simulates an atmosphere primarily composed of co2 ( 90 bars) and n2 ( 3 bars) with trace amounts of h2o, so2, hcl, and other constituents composed of h, c, o, n, s, and cl, which contribute the hox, clox, sox, and nox catalysts that can recombine photochemically generated co and o into co2. we compare the effect of g- and m-dwarf spectral energy distributions on venus-like worlds, placing the planets at orbital distances with the same total incident flux as venus. we find that venus-like worlds are rich in catalysts that can recombine co and o into co2. around both g and early m dwarfs, as the catalytic clox chemistry is sufficient recombine co and o. we identify catalytic cycles involving cl-s molecules that control the buildup of large amounts of photochemical o2 around late m dwarfs. specifically, around trappist-1, low so2 mixing ratios significantly reduces the action of cl-s catalysts that scrub o2 and reconstitute co2. this implies that venus-like planets around late m dwarfs must maintain some amount of active so2 outgassing to be robust against abiotic o2 production. | abiotic oxygen on venus-like exoplanets around m-dwarfs |
terrestrial planets in temperate orbit around very low mass stars are likely to have evolved in a very different way than solar system planets, and in particular earth. however, because these are the first planets that are and will be accessible for in-depth atmosphere, clouds and surface characterizations with existing and forthcoming telescopes, we need to develop the best possible observational strategies to maximize the scientific return from these characterizations. here i discuss and expand on the recent works of \citet{bean:2017} and \citet{turbet:2019aa} to show that terrestrial planets orbiting in temperate orbits around very low mass stars are potentially an excellent sample of planets to test how universal the processes thought to control the habitability of solar system planets and in particular earth are. precise measurements of density or amospheric co_2 concentration for planets located both inside and outside the habitable zone could be used to statistically test habitability concepts such as the silicate-weathering feedback, co_2 condensation, or runaway greenhouse, which have been identified as key processes controlling the present and past habitability of venus, mars and earth. | two examples of how to use observations of terrestrial planets orbiting in temperate orbits around low mass stars to test key concepts of planetary habitability |
planets similar to earth - but slightly more irradiated - are expected to enter into a runaway greenhouse state, where all surface water rapidly evaporates, forming an optically thick water-dominated atmosphere. here we take advantage of this runaway greenhouse process to propose a new, innovative observational test of the habitable zone concept, that could also be used to diagnose the presence of water in temperate, earth-size exoplanets such as the trappist-1 system. | towards the detection of the runaway greenhouse radius inflation effect |
among different models for determining the habitable zone (hz) around a star, a latitudinal energy balance model (lebm) is very beneficial due to its parametricity which keeps a good balance between complexity and simulation time. this flexibility makes the lebm an excellent tool to assess the impact of some key physical parameters on the temperature and the habitability of a planet. among different physical parameters, some of them, up until now, cannot be determined by any method such as the planet's spin obliquity, diurnal period, ocean-land ratio, and pressure level. here we apply this model to study the effect of these unknown parameters on the habitability of three exoplanets located in the inner, outer, and middle of their optimistic hz. among the examined parameters, the impact of pressure is more straightforward. it has a nearly direct relation with temperature and also with the habitability in the case of a cold planet. the effect of other parameters is discussed with details. to quantify the impact of all these unknown parameters we utilize a statistical interface which provides us with the conditional probability on habitability status of each planet. | evaluating the effect of four unknown parameters included in a latitudinal energy balance model on the habitability of exoplanets |
an obvious new frontier for humanity is to locate our nearest neighbors technically advanced (eti, extra-terrestrial intelligence), in response to the question "are we alone in the universe?" this quest can be achieved with three steps: 1. find the nearest exoplanets in the habitable zone (hz) of their host stars. 2. find bio-signatures in their atmospheric and surface spectra. 3. find unvolontary signs of advanced technology (city lights at night, radio signal leaks). we argue that steps 2 and 3 will require large space telescopes that need to be oriented to targets already identified in step 1 as hosting exoplanets of earth or super earth size in the habitable zone. we show that non-transiting planets in hz are 3 to 9 times nearer the sun than transiting planets, the gain factor being a function of star temperature. the requirement for step 1 is within the reach of a network of 2-4 m diameter ground-based automated telescopes associated with harps-type spectrometers. the search should be done by increasing distance from our sun. steps 2 and 3 will require the building in space of large size telescopes, which elements could launched separately, and be assembled in space by astronauts, in a fashion similar to the way was built the international space station. the telescopes could also be placed on the moon or at lagrange l2 point. since eti can spot us, we must be able to spot them. communication is an independent matter to be discussed separately. the author acknowledge support from the russian government grant #14.w03.31.0017. | a three-steps road map to the new frontier: locating the nearest etis, and the role of astronauts. |
neid is an ultra-stable, optical spectrometer designed to achieve radial velocity (rv) precision on the order of 10cm/s. achieving this level of measurement precision requires extreme thermo-mechanical stability within the instrument which we achieve by maintaining a vacuum on the order of microtorr as well as sub-millikelvin temperature stability. in this poster, we will outline neid's environmental control system (ecs) and temperature monitoring and control (tmc) system, which were both inherited and improved upon from that of the habitable-zone planet finder (hpf) infrared spectrograph. we have achieved our target stability by demonstrating < 0.4mk rms temperature variability over the course of a 30 day stability run in the lab. we expect our stability to improve at the observatory as the wiyn instrument room is more stable than our instrument development lab. neid will be commissioned in midwinter 2019 at kitt peak national observatory on the 3.5m wiyn telescope. it will serve the exoplanet community as a vital follow up asset for earth-like planets targeted by the tess survey. | design and performance of neid ultra-stable environmental control system |
the discovery of short-period planets with masses and radii intermediate between earth and neptune was one of the biggest surprises in the brief history of exoplanet science. these “super-earths” and “sub-neptunes” are an order of magnitude more abundant than close-in giant planets. despite this ubiquity, we know little about their typical compositions and formation histories. spectroscopic transit observations can shed new light on these mysterious worlds by probing their atmospheric compositions. in this talk, we will give an overview of our ongoing 124-orbit (200-hour) hubble space telescope program to reveal the chemical diversity and formation histories of super-earths. this unprecedented survey will provide the first comprehensive look at this intriguing new class of planets ranging from 1 neptune mass and temperatures close to 2000k to a 1 earth mass planet near the habitable zone of its host star. in this talk, i will discuss the scope of the program and present early science results including measurements of water absorption in the atmosphere of the warm exo-uranus gj3470b. | measurements of water absorption in the warm exo-uranus gj 3470b |
stellar flares are the most dramatic examples of energy release that non-degenerate stars undergo while on the main sequence. in our search for habitable zone planets around m dwarf stars, characterizing the flare activity of m dwarfs is a key ingredient to understanding the impact the star can have on its near stellar environment. recent results have also demonstrated that particle acceleration in the stellar atmosphere plays a crucial role in the shape and amount of uv and optical radiation released during m dwarf flares. the nuv range is unequivocally a "fulcrum'' between the optical and shorter wavelength fuv continua but has been woefully undersampled in observations. we propose a hst treasury program to characterize the nuv continuum and emission lines in m dwarf stellar flares. only hst can empirically constrain the spectral peak and slope in the nuv and thus physically explain the origin of the flare in the low stellar atmosphere through the heating by accelerated particles. our strategy spans a 4.5x greater spectral range in the nuv than previous studies and will provide flux-calibrated, time-resolved flare spectra just below the atmospheric cutoff (lam < 3200 a). the flare and quiescent data will have broad legacy value for characterizing the high-energy radiation environment of exoplanets, comparing to iris data of solar flares, and interpreting archival broadband nuv photometry of magnetically active stars. the science products -- time-resolved nuv spectra along with best-fit models to the nuv spectra calculated on a wider wavelength range from fuv through red-optical wavelengths -- will also benefit multiple communities. | from high-energy particle beam heating in stars to ozone destruction in planets: nuv spectra as the fulcrum for a comprehensive understanding of flaring m dwarf systems |
the observations of the kepler space telescope suggest that small planets are abundant around cool main-sequence stars, among which late-m dwarfs (lmds) represent the coolest objects. lmds are the great targets for the exoplanet search with the radial velocity (rv) technique due to their relatively low masses and inner habitable zones. however, lmds are so faint especially at optical wavelengths that the rv technique for lmds needs the infrared spectrograph available on a large-aperture telescope with a stable calibration system of rv measurement. we have developed and operated the infrared doppler (ird) spectrograph that can be utilized with the adaptive optics of the subaru telescope. ird observes a laser frequency comb simultaneously with an object spectrum, enabling the stable rv calibration comparable to 2 m s-1 at 1.0-1.7 μm. since february of 2019, we have started a strategic campaign to explore planets around lmds using ird, which is planned to go on until 2024 with the total allocation of 175 nights. this is the first large-scale survey dedicated to lmds that is achieved by the precision rv measurements in the infrared. the ird survey is expected to discover habitable planets that can be characterized in detail with next generation telescopes. also, the monitor of lmds over a few years can reveal the population of rocky to ice-giant planets inside and outside of snow lines. we have listed 150 targets based on the literature and our pre-selection spectroscopic observations to filter out active lmds unsuitable for precision rv measurements. in addition, the rapid rotators and close-separation multiple stars are removed through the first-year ird observations, selecting the best 60 lmds for extensive rv measurement. in parallel with the science observations, we are testing the precision and stability of our rv measurements by observing rv-stable stars and planet-host stars such as gj 699 and gj 436. we here present the strategy of the ird planet survey and its latest progress, as well as the results of the performance verification. | the beginning of the strategic large exploration for exoplanets orbiting nearby late-m dwarfs with the infrared doppler (ird) spectrograph on the subaru telescope |
the star 55 cancri was one of the first known exoplanet hosts and each of the planets in this system is remarkable. planets b and c are in a near 1:3 resonance. planet d has a 14.5 year orbit, and is one of the longest known orbital periods for a gas giant planet. planet e has a mass of 8 m? and transits this bright star, providing a unique case for modeling of the interior structure and atmospheric composition of an exoplanet. planet f resides in the habitable zone of the star. if the planets are approximately co-planar, then by virtue of having one transiting planet, this is a system where the doppler technique has essentially measured the true mass of the planets, rather than just msin i. the unfolding history of planet discovery for this system provides a good example of the challenges and importance of understanding the star to understand the planets. | 55 cancri (copernicus): a multi-planet system with a hot super-earth and a jupiter analogue |
in the perspective of detecting and characterizing more and more close-in-orbit hot terrestrial exoplanets transiting nearby m-dwarf stars (e.g., best earth-size targets for observational studies), the atmosphere of our "sister" planet venus is one of the most relevant cases to address observational prospects. the detection of venus-like atmospheres at various orbital periods and planetary masses will create a picture of where the divergence between earth and venus originates [1].in this work, we propose to use a 3d global climate model (gcm) developed explicitly for exoplanets and paleoclimate studies [2] to simulate the atmospheres of a possible class of venus-like exoplanets i.e., rocky, highly irradiated exoplanets orbiting m-dwarf stars. the objectives are twofold: 1) to study the impact of changing specific planetary parameters, e.g., planetary radius and gravity, in the large-scale atmospheric circulation; and 2) to reproduce synthetic emission and reflected phase curves capable of addressing observational prospects.1.introduction in the solar system, venus and the earth are examples of two rocky planets with similar radii and mass values and possibly a similar bulk composition [3]. nonetheless, the two planets also represent a scenario of divergent climate evolution. thus, in terms of mass and radius parameters, venus and earth would be astrophysically indistinguishable in the event we would be observing them as exoplanets. several modelling studies [4] established possible limits for both the habitable zone and the "venus zone" [1]. these 1d modelling studies offered a first approximation for the future differentiation between earth-like and venus-like exoplanet populations. nonetheless, the complete characterisation and differentiation between these two populations can only be currently accomplished with dedicated 3d gcms, which can reproduce the sort of climate feedbacks that ultimately constraint surface habitability conditions [5]. the diversity of planetary climates is expected to be significant given 1) the variety of planetary atmospheres on the rocky worlds of our solar system 2) the diversity of the planetary parameters for the exoplanets observed so far. thus, predicting the actual climate for a specific planet represents a challenging task [6]. a new era for characterising rocky exoplanet atmosphere will be opened by the james webb space telescope (jwst), foreseen to be launched in 2021 and continued by the esa mission ariel scheduled for launch in 2029. in addition, a new generation of instruments is being developed, including a whole set of new high-resolution spectrographs for the very large telescopes (vlt) and extremely large telescopes (elt). 2.gcm modelling of venus analogues we propose using the generic gcm firstly developed at the laboratoire de meteorologie dynamique (hereinafter lmd g-gcm) to simulate venus-like exoplanetary atmospheres and climate response to a realistic set of planetary parameters. we will also provide synthetic observables, reflected and emission phase curves, which are inherently 3d, to support the characterisation of the population of venus-like exoplanets in the future. the lmd g-gcm uses a 3d dynamical core, common to all terrestrial planets, and a planet-specific physical core. it includes an up-to-date generalised radiative transfer for variable gaseous atmospheric compositions made of various cocktails of co2, n2, and h2o, o2, co, using the correlated-k method. processes such as the radiative effect of clouds or rayleigh scattering are considered. for instance, it has successfully been used to simulate the climate of other exoplanets like the cold super-earth gliese 581d, a tidally-locked exoplanet like gliese 581c/hd85512b [2], or proxima b [5]. in this work, the lmd g-gcm is adapted to study close-in venus-like exoplanets orbiting m-dwarf stars. the work is focused on the response of large-scale atmospheric circulation to critical parameters: radius, gravity, surface atmospheric pressure, solid-body rotation rate. for the latter, we will be selecting two likely modes, 1:1 and 3:2 spin-orbit resonances. each parameter will be changed while keeping the others fixed. combinations of realistic parameter variations will be selected according to specific mass-radius relationships [7]. this will allow for the characterisation of temperature and wind fields at different pressure levels, particularly at and above the classical venus top cloud layer. 3.preliminary results to address the impact from simulating hot, dense atmospheres typical for venus-like exoplanets, we run the lmd g-gcm using the planetary parameters of exoplanet trappist-1c as a framework for a possible venus-like exoplanet. synchronous rotation, with no obliquity and eccentricity, were assumed, together with a venus-like atmosphere, with 92-bar surface pressure, and similar chemical composition with radiatively active venus-type clouds, uv absorbers, and meridional variation of the cloud structure [8]. quasi-convergence of temperature is achieved for the whole atmosphere after 15000 orbits (see fig.1). using the last orbit, the quasi-steady state obtained will be taken as the initial state to run simulations varying the parameters space, allowing the study of atmospheric variables (see fig.2). in addition, top-of-the-atmosphere longitude-latitude maps of outgoing fluxes computed by the lmd g-gcm will be used to produce phase curves and interpret possible variations due to atmospheric dynamics (e.g., superrotation, jets, waves). figure 1. temperature profile (solid black line) for the quasi-steady state, used as a reference input for future simulations. the initial profile (thin blue line) is obtained after running the model for 300 days for a venus-like planet orbiting a sun-like star. figure 2. instantaneous temperature field for the cloud-top pressure level (p~0.02-bar) for trappist-1c, 300 orbits after the quasi-steady state was obtained. the sub-stellar point is represented by the white star. acknowledgments this work is supported by fundação para a ciência e a tecnologia (fct) through the research grants uidb/04434/2020, uidp/04434/2020, p-tuga ptdc/fis-ast/29942/2017.references[1] kane et al.2018. apj.869[2] wordsworth et al.2011. apjl. 733. l48.[3] hamano et al. 2013. nature, 497, 607-610[4] kopparapu et al.2014. apjl. 787.l29.[5] turbet et al.2016. a&a. 596. a112.[6] forget & leconte 2014. phil. trans. r. soc.a372.[7] zeng et al.2016. apj. 819. 127.[8] garate-lópez & lebonnois 2018 icarus 314. | planetary parameters impact in the large-scale circulation of venus-like exoplanetary atmospheres and observational prospects |
the frequency of earth-like planets in the habitable zone of sun-like stars (ηearth) is a fundamental input in estimating the occurrence rate of life resembling that on earth, and therefore an important parameter for designing future direct imaging missions. ηearth is currently best estimated by the kepler transit survey, but earth-analog systems with long periods and shallow transits are on the edge of the survey's sensitivity. the roman galactic exoplanet survey will be able to detect earth-analog systems through microlensing, but similarly they will be on the boundary of its sensitivity due to low-mass ratios and small projected separations. we perform simulations of the roman galactic exoplanet survey to estimate its sensitivity to these systems. roman's ability to estimate ηearth will hinge on the extrapolation from systems with larger mass-ratios and wider projected separations. finally, we consider the possibility of improving the fidelity of estimates of ηearth by interpolating between the results from roman and kepler by adopting a mass-radius relation for earth-like planets. | the roman galactic exoplanet survey: prospects for constraining the frequency of earth-analogs |
solar system planets move on almost circular orbits. in strong contrast, many massive gas giant exoplanets travel on highly elliptical orbits, whereas the shape of the orbits of smaller, more terrestrial, exoplanets remained largely elusive. this is because the stellar radial velocity caused by these small planets is extremely challenging to measure. knowing the eccentricity distribution in systems of small planets would be important as it holds information about the planet's formation and evolution. furthermore the location of the habitable zone depends on eccentricity, and eccentricity also influences occurrence rates inferred for these planets because planets on circular orbits are less likely to transit. we make these eccentricity measurements of small planets using photometry from the kepler satellite and utilizing a method relying on kepler's second law, which relates the duration of a planetary transit to its orbital eccentricity, if the stellar density is known.i present a sample of 28 multi-planet systems with precise asteroseismic density measurements, which host 74 planets with an average radius of 2.6 r_earth. we find that the eccentricity of planets in these systems is low and can be described by a rayleigh distribution with sigma = 0.049 +- 0.013. this is in full agreement with solar system eccentricities, but in contrast to the eccentricity distributions previously derived for exoplanets from radial velocity studies. i further report the first results on the eccentricities of over 50 kepler single-planet systems, and compare them with the multi-planet systems. i close the talk by showing how transit durations help distinguish between false positives and true planets, and present six new planets. | eccentricity of small exoplanets |
the transiting exoplanet survey satellite (tess) will discover thousands of exoplanets in orbit around the brightest stars in the sky. in its two-year prime survey mission, tess will monitor more than 200,000 bright stars in the solar neighborhood for temporary drops in brightness caused by planetary transits. this first-ever spaceborne all-sky transit survey will identify planets ranging from earth-sized to gas giants, around a wide range of stellar types and orbital distances.tess stars will typically be 30-100 times brighter than those surveyed by the kepler satellite; thus, tess planets will be far easier to characterize with follow-up observations. for the first time it will be possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars.an additional data product from the tess mission will be full frame images (ffi) with a cadence of 30 minutes or less. these ffi will provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the tess cameras. these objects will include more than 1 million stars and bright galaxies observed during sessions of several weeks. in total, more than 30 million objects brighter than i=16 will be precisely photometered during the two-year prime mission. in principle, the lunar-resonant tess orbit could provide opportunities for an extended mission lasting more than a decade, with data rates in excess of 100 mbits/s.an extended survey by tess of regions surrounding the north and south ecliptic poles will provide prime exoplanet targets for characterization with the james webb space telescope (jwst), as well as other large ground-based and space-based telescopes of the future.tess will issue data releases every 4 months, inviting immediate community-wide efforts to study the new planets, as well as commensal survey candidates from the ffi. a nasa guest investigator program is planned for tess. the tess legacy will be a catalog of the nearest and brightest main-sequence stars hosting transiting exoplanets, which should endure as the most favorable targets for detailed future investigations.tess is targeted for launch in 2017 as a nasa astrophysics explorer mission. | the transiting exoplanet survey satellite (tess): discovering new earths and super-earths in the solar neighborhood |
the full data set of known exoplanets was downloaded from the nasa exoplanet archive using the application programming interface. for planets that were missing stellar luminosity, luminosity was calculated using the stefan-boltzmann law. when unavailable, the stellar radius was calculated from the stellar mass and surface gravity. (1 data file). | vizier online data catalog: habitable zone exoplanets from nasa exoplanet archive (hill+, 2023) |
in 2016, a star kic 8462852 caught the world's attention due to a paper by citizen scientists who noticed its seemingly unexplainable brightness variations. the forward theory was offered - kic 8462852 is surrounded by a dyson sphere, a megastructure made by an alien civilization to collect all energy output from their star. finally, in 2018, its light curve showed chromaticity more characteristic of the dust (from comets or asteroids) rather than of something made from solid material, but the world was woken up to the idea of megastructures. but, in dyson's time, only solar system planets were known; it took more than 20 years to realize that nature has no problem making planets and does it with a flair -- the total number of planets in the galaxy is estimated to be in billions. with such abundance of planets, there would be no need to destroy the entire planetary system to make one sphere. instead, a civilization can expand to a system that has planet(s) in the habitable zone (hz), or a planet can be moved into it. alternatively, a free-floating planet (ffp) can be captured and moved into the hz. these shifts can be performed at a constant low-thrust acceleration using high power directional lasers, resulting in a gradual spiral transfer from one orbit to another. we propose here to search for eti by looking for high-power laser technosignatures and consider merits of such signatures. we suggest to specifically pay attention to the multiple planetary systems that have strange exoplanetary architectures (sea) - unusual planetary arrangements that cannot be explained by current planetary formation theories, because these could be the result of eti moving planets intentionally to suit their needs. | making habitable worlds: planets versus megastructures |
traditionally, the search for life on exoplanets has been predominantly focused on rocky exoplanets. hycean worlds are a class of habitable sub-neptunes with planet-wide oceans and h2-rich atmospheres. their broad range of possible sizes and temperatures lead to a wide habitable zone and high potential for discovery and atmospheric characterization using transit spectroscopy. over a dozen candidate hycean planets are already known to be transiting nearby m dwarfs, making them promising targets for atmospheric characterization with the james webb space telescope (jwst). in this work, we investigate possible chemical conditions on a canonical hycean world, focusing on (a) the present and primordial molecular composition of the atmosphere, and (b) the inventory of bioessential elements for the origin and sustenance of life in the ocean. based on photochemical and kinetic modeling for a range of conditions, we discuss the possible chemical evolution and observable present-day composition of its atmosphere. in particular, for reduced primordial conditions the early atmospheric evolution passes through a phase that is rich in organic molecules that could provide important feedstock for prebiotic chemistry. we investigate avenues for delivering bioessential metals to the ocean, considering the challenging lack of weathering from a rocky surface and the ocean separated from the rocky core by a thick icy mantle. based on ocean depths from internal structure modelling and elemental estimates for the early earth's oceans, we estimate the requirements for bioessential metals in such a planet. we find that the requirements can be met for plausible assumptions about impact history and atmospheric sedimentation, and supplemented by other steady state sources. we discuss the observational prospects for atmospheric characterisation of hycean worlds. | chemical conditions on hycean worlds |
by now, observations of exoplanets have found more than 50 binary star systems hosting 71 planets. we expect these numbers to increase as more than 70% of the main sequence stars in the solar neighborhood are members of binary or multiple systems. the planetary motion in such systems depends strongly on both the parameters of the stellar system (stellar separation and eccentricity) and the architecture of the planetary system (number of planets and their orbital behaviour). in case a terrestrial planet moves in the so-called habitable zone (hz) of its host star, the habitability of this planet depends on many parameters. a crucial factor is certainly the amount of water. we investigate in this work the transport of water from beyond the snow-line to the hz in a binary star system and compare it to a single star system. | impact flux of asteroids and water transport to the habitable zone in binary star systems |
we explore the large-scale climate dynamics at low and high obliquity for an earth-like planet using the rocke-3d (resolving orbital and climate keys of earth and extraterrestrial environments with dynamics) 3-d general circulation model being developed at nasa giss as part of the nexus for exoplanet system science (nexss) initiative. we highlight the role of ocean heat storage and transport in determining the seasonal cycle at high obliquity, and describe the large-scale circulation and resulting regional climate patterns using both aquaplanet and earth topographical boundary conditions. finally, we contrast the hysteresis structure to varying co2 concentration for a low and high obliquity planet near the outer edge of the habitable zone. we discuss the prospects for habitability for a high obliquity planet susceptible to global glaciation. | climate dynamics and hysteresis at low and high obliquity |
we introduce a mathematical framework for statistical exoplanet population and astrobiology studies that may help direct future observational efforts and experiments. the approach is based on a set of differential equations and provides a time-dependent mapping between star formation, metal enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemo-population history of the solar neighborhood. our results are summarized as follows: (1) the formation of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about 11 gyr ago; (2) within 100 pc from the sun, there are as many as 11,000(η ⊕/0.24) earth-size planets in the habitable zone ("temperate terrestrial planets" or ttps) of k-type stars. the solar system is younger than the median ttp, and was created in a star formation surge that peaked 5.5 gyr ago and was triggered by an external agent; (3) the metallicity modulation of the giant planet occurrence rate results in a later typical formation time, with ttps outnumbering giant planets at early times; and (4) the closest, life-harboring earth-like planet would be ≲20 pc away if microbial life arose as soon as it did on earth in ≳1% of the ttps around k stars. if simple life is abundant (fast abiogenesis), it is also old, as it would have emerged more than 8 gyr ago in about one-third of all life-bearing planets today. older earth analogs are more likely to have developed sufficiently complex life capable of altering their environment and producing detectable oxygenic biosignatures. | beyond the drake equation: a time-dependent inventory of habitable planets and life-bearing worlds in the solar neighborhood |
one of the greatest challenges in astrobiology is understanding the distribution of life in the universe based on a single example: earth. in order to address this limitation, several astronomical surveys monitored hundreds of thousands of stars over the three past decades and found more than 4900 exoplanets around them. although a perfect earth-sun analog system remains elusive due to technical limitations, many of the discovered exoplanets lie within the habitable zones of their host stars and could be suitable for life as we know it. in this contribution, i will briefly review the most successful methods for detecting exoplanets, what planetary properties can be inferred and how these can be used to estimate if the planet is potentially habitable. i will also present a list of the best candidates for hosting life and discuss perspectives for detecting biosignatures in their atmospheres using space and ground-based telescopes that will start operating in the near future. | the search for habitable planets |
the search for exoplanets has revealed a diversity of planetary system architectures, the vast majority of which diverge significantly from the template of the solar system. in particular, giant planets beyond the snow line are relatively rare, especially for low-mass stars, placing the solar system within a small category of systems with multiple giant planets at large separations. an exoplanetary system of note is that of hd 141399, consisting of a k-dwarf host star that harbors four giant planets with separations extending to ~4.5 au. the architecture of the system creates a complex pattern of mean motion resonances and gravitationally perturbed regions that may exclude the presence of other planets, including within the habitable zone of the system. here, we present the results of dynamical simulations that explore the interaction of the known planets of the system, their apsidal trajectories, resonance locations, and dynamical evolution. we further investigate the results of injecting earth-mass planets and provide the regions of dynamical viability within the habitable zone where terrestrial planets may maintain long-term stability. we discuss these results in the context of the importance of giant planets for volatile delivery and planetary habitability considerations. | surrounded by giants: habitable zone stability within the hd 141399 system |
earth-like planets orbiting m-dwarf stars, m-earths, are currently the best targets to search for signatures of life. life as we know it requires water. the habitability of m-earths is jeopardized by water loss to space: high flux from young m-dwarf stars can drive the loss of 3-20 earth oceans from otherwise habitable planets. we develop a 0-d box model for earth-mass terrestrial exoplanets, orbiting within the habitable zone, which tracks water loss to space and exchange between reservoirs during an early surface magma ocean phase and the longer deep-water cycling phase. a key feature is the duration of the surface magma ocean, assumed concurrent with the runaway greenhouse. this time-scale can discriminate between desiccated planets, planets with desiccated mantles but substantial surface water, and planets with significant water sequestered in the mantle. a longer-lived surface magma ocean helps m-earths retain water: dissolution of water in the magma provides a barrier against significant loss to space during the earliest, most active stage of the host m-dwarf, depending on the water saturation limit of the magma. although a short-lived basal magma ocean can be beneficial to surface habitability, a long-lived basal magma ocean may sequester significant water in the mantle at the detriment of surface habitability. we find that magma oceans and deep-water cycling can maintain or recover habitable surface conditions on earth-like planets at the inner edge of the habitable zone around late m-dwarf stars - these planets would otherwise be desiccated if they form with less than ~10 terrestrial oceans of water. | the role of magma oceans in maintaining surface water on rocky planets orbiting m-dwarfs |
the continuous discovery of exoplanets, each with distinctive stellar and planetary properties, along with the development of higher resolution ground and space telescopes have positioned climate evolution as a fundamental component in the study of planetary habitability. in particular, the planet gl 514 b is located within the habitable zone of an m0 type star that is 24.85 light-years from earth, and therefore is a candidate for direct observations with future 30m class ground-based telescopes. one aspect of interest of this planet is its eccentricity of 0.45±0.15, which could dramatically affect the seasonal climate. hence, we simulated a plausible range of climates on this planet to both assess its likelihood to be habitable as well the ice coverage of the surface, which could affect the photometric signal. to perform these simulations, we used vplanet's energy balance and tidal models to explore the parameter space permitted by the observations and the range allowed by the theoretical models. we include tidal modeling since, for isolated planets, tides will increase the obliquity then reduce it to 0 over approximately 1 gyr and can therefore affect the early climate evolution of the planet. these results help determine the orbital, rotational, and physical conditions required for habitability of gl 514 b and will therefore help guide future direct-imaging surveys. | the climates of gl 514 b |
a major emerging focus of exoplanet research is the role of runaway greenhouse phases in the habitability of rocky planets near the inner edge of the habitable zone. new evidence points to large water reservoirs in the interior of these planets if their surface was hot enough to be molten during their evolution. planetary radius changes due to this water incorporation, in addition to the presence of steam atmospheres, must leave an imprint on the distributions of planetary bulk parameters. we use bioverse, a simulation framework that leverages the contextual information from the overall planet population, to assess the ability of space and ground-based telescopes to test this hypothesis. in the near future, esa's plato mission and nasa's roman space telescope will be the most promising endeavors to constrain this demographic feature. for each of these missions, we identify the key mission design drivers that enable a statistically sound detection. we also discuss their potential to constrain key open parameters in the theory of global magma oceans. | the imprint of global magma oceans on exoplanet demographics |
as the search for exoplanets continues, more are being discovered orbiting red giant stars. we use current data from the nasa exoplanet archive to investigate planet distribution around red giant stars and their presence in the host's habitable zone. as well, we explore the distribution of planet mass and orbital semi major axis for evolved stars with increasing stellar radii. from the distance distribution of the planets, we found evidence of engulfment during the post-main sequence evolution of the star. we found 9 red giant-hosted exoplanets, and 21 subgiant-hosted exoplanets to be in the optimistically calculated habitable zone, 5 and 17 of which are in a more conservatively calculated habitable zone. all the planets detected within their habitable zone orbit stars that are in early stages of evolution. we believe that with more powerful instrumentation, more habitable planets may be found around stars that are in later stages of evolution. | exoplanets around red giants: distribution and habitability |
the long-term stability of exoplanetary atmospheres depends critically on the extreme-ultraviolet (euv) photon and high-energy particle fluxes from the host star. the euv flux also drives the demographics of the short-period planet population and regulates the ability for rocky planets to maintain habitable environments long enough for the emergence of life. in this talk, i will present the extreme-ultraviolet stellar characterization for atmospheric physics and evolution (escape) mission, an astrophysics small explorer mission to be submitted to the upcoming astrophysics small explorer call. escape employs extreme- and far-ultraviolet spectroscopy (80 - 1650 angstroms) to characterize the high-energy radiation environment in the habitable zones around nearby stars. escape provides the first comprehensive study of the stellar euv and stellar coronal mass ejection (cme) environments that control atmospheric mass-loss and determine the habitability of rocky exoplanets. escape will survey over 200 stars, including known planet hosts, to measure euv irradiance, euv flare rates, and the properties of cmes. the escape instrument comprises a grazing incidence telescope feeding multiple diffraction gratings and a photon-counting detector. the science instrument will be assembled and tested in the space hardware facilities at the university of colorado boulder's laboratory for atmospheric and space physics. data archives will reside at the mikulski archive for space telescopes (mast). | the extreme-uv radiation environment of extrasolar planets: the escape small explorer mission |
the success of the transiting exoplanet survey satellite mission has led to the discovery of an abundance of venus zone terrestrial planets that orbit relatively bright host stars. atmospheric observations of these planets play a crucial role in understanding the evolutionary history of terrestrial planets, past habitable states, and the divergence of venus and earth climates. the transmission spectrum of a venus-like exoplanet can be difficult to distinguish from that of an earthlike exoplanet however, which could severely limit what can be learned from studying exovenuses. in this work we further investigate differences in transmission between hypothetical exoearths and exovenuses, both with varying amounts of atmospheric carbon dioxide (co2). the exoearths and exovenuses were modeled assuming they orbit trappist-1 on the runaway greenhouse boundary. we simulated james webb space telescope near-infrared spectrograph prism transit observations of both sets of planets between 0.6 and 5.2 μm, and quantified the detectability of major absorption features in their transmission spectra. the exoearth spectra include several large methane (ch4) features that can be detected in as few as six transits. the ch4 feature at 3.4 μm is the optimal for feature for discerning an exoearth from an exovenus since it is easily detectable and does not overlap with co2 features. the sulfur dioxide (so2) feature at 4.0 μm is the best indicator of an exovenus, but it is detectable in atmospheres with reduced co2 abundance. | reading between the lines: investigating the ability of jwst to identify discerning features in exoearth and exovenus transmission spectra |
the new earths in the alpha cen region campaign is a 100-h imaging search for massive rocky planets in the habitable zone of the two stars of alpha cen. the program is a collaboration between the breakthrough initiatives and eso and was launched in 2016. to achieve the challenging goal of near, the vlt mir instrument visir was upgraded and installed at ut4 to couple it with the adaptive optics facility. the university of liege provided an optimized vortex coronagraph and a dedicated pointing control procedure. after a successful commissioning in april and may 2019, the campaign was completed in may-june 2019. it generated >6 tb of data, which are available to the community. the data were analyzed by the near collaboration. i will present the science context of the project, simulated and on-sky results of the performance of the vortex coronagraph, the lessons learned for high-contrast imaging with elt metis, and prospects for imaging earth-mass planets around alpha cen. | lessons learned from near for high-contrast imaging of exoplanets with elt metis |
many main sequence stars have chromospheric activity levels that vary with time. these can be characterized based on their ca ii h and k line core emission. using data obtained from the california planet search we fit a sinusoidal function to a sample of 244 stars to test for significant cyclic variability. we wrote a python program to analyze observations taken over timescales of up to 17 years to determine optimal sinusoidal parameters, with uncertainties estimated through a bootstrapping technique. we also identify some inactive stars with virtually no r'hk variability. we find that within our sample the less active cyclic stars tend to have longer periods. ongoing work examines the potential impact of cyclic and flaring stellar activity on known exoplanets, including those orbiting within the habitable zone. | stellar activity of main sequence stars |
many earth-sized planets have been discovered and some of them are potentially in the habitable zone. in addition, several earth-sized planets have been detected around low temperature stars near our solar system. however, it is difficult to characterize them as earth-like or venus-like, even though they are relatively very close to our solar system. we performed a conceptual design of an ultraviolet spectrograph for exoplanet (uvspex) for world space observatory ultraviolet (wso-uv), which is 1.7-m uv space telescope being prepared by russia. the spectral range is to exceed wavelengths from 115 nm to 135 nm to detect at least h lyman alpha 121.6nm to o i 130 nm. the throughput is >4%. uvspex is planned to be a part of a field camera unit (fcu). this additional instrument would enable us to observe ~20 earth-like exoplanets and detect an oxygen exosphere if some of them have an earth-like atmosphere. | uvspex/wso-uv for earth-like exoplanetary oxygen exospheres |
future space missions such as the large uv-optical-infrared surveyor (luvoir) and the habitable exoplanet observatory (habex) require large apertures and coronagraphs with active wavefront control to be able to suppress the starlight so faint planets can be detected and characterized adjacent to their parent star.the extreme coronagraph for living planet systems (eclips) is the coronagraph instrument on the luvoir surveyor mission concept, an 8-15m segmented telescope. eclips is split into three channels: uv (200 to 400 nm), optical (400 nm to 850 nm), and nir (850 nm to 2.0 microns), with each channel equipped with two deformable mirrors for wavefront control, a suite of coronagraph masks, a low-order/out-of-band wavefront sensor, and separate science imagers and spectrographs.the apodized pupil lyot coronagraph (aplc) and the vector vortex coronagraph (vvc) are the baselined mask technologies for eclips to enable the required 1e10 contrast for observations in the habitable zones of nearby stars. their performance depends on active wavefront sensing and control, as well as metrology subsystems to compensate for static aberrations induced by segment errors (piston and tip/tilt, among others), secondary mirror misalignment, and global low-order wavefront errors. here we present the latest results of the simulation of these effects for the two technologies, as well as the effects of dynamic aberrations such as segment jitter, segment drift and line of sight pointing errors, and discuss the achieved contrast for exoplanet detection and characterization. finally, we show simulated observations using high-fidelity spatial and spectral input models of complete planetary systems generated with the haystacks code framework, setting boundaries for tolerance of such errors. | sensitivity to telescope aberrations for exoplanet detection with the luvoir coronagraph instrument eclips |
the search for earth-sized exoplanets around low-mass stars is rapidly gaining attention because they represent the best opportunity to characterize habitable planets in the near future. it is essential that we understand the atmospheres of these tidally-locked planets and determine the optimal strategy for characterizing them with our upcoming observing capabilities. to quantify how well we can constrain the properties of the atmospheres of these planets, we utilize gcm simulations of synchronously rotating earth-like planets orbiting m and k stars to produce simulated transmission, eclipse and phase-resolved spectra. our first study determined the exposure times necessary to detect water vapor in the atmospheres of hypothetical ocean worlds using transmission spectra with the upcoming james webb space telescope (jwst) as well as several future flagship space telescope concepts under consideration (luvoir and ost) for the brightest cool stars from the tess input catalog (tic). we then modeled a recently discovered earth-sized exoplanet in the habitable zone of an m dwarf, but over a wide range of possible atmospheric conditions. we ran a suite of gcm simulations considering modern-earth, archean-earth, and early-mars-type atmospheres for both an ocean-covered and desiccated planet. we present the results of both studies, and gauge the necessary instrumentation capabilities necessary to characterize the potentially habitable planets with upcoming space-based observatories. | exploring habitable-zone earths in synchronous rotation around cool stars with general circulation models and simulated spectra |
machine learning has been successfully used to rapidly classify transit signals (e.g., as planet candidates or false positives) in light curves from the kepler mission using deep convolutional neural networks. however, these machine learning models depend on traditional exoplanet detection pipelines (e.g., the kepler science processing pipeline) to first identify the transit signals with brute-force methods, such as box least squares periodogram searches across all possible periods on significantly pre-processed data (i.e., after light curve extraction and flattening). moreover, the currently available training set for kepler data is limited to only ~15,000 labeled examples, whereas successful supervised machine learning applications typically have at least an order of magnitude more; additionally, these labeled examples are mostly false positives (e.g, eclipsing binaries, instrumental artifacts) or planet candidates with high snr (e.g., close-in giant planets), making it difficult to train models that can reliably identify low snr transits that correspond to interesting cases such as rocky planets in the habitable zone. advances in using machine learning to mine the kepler data will therefore depend on the construction of much larger and more balanced training datasets, such as via innovative data augmentation techniques or more realistic injected light curves. the biggest breakthroughs will be in developing methods for using machine learning to detect (rather than just classify) exoplanet transits, not just in the light curves but also in the less processed target pixel files. | how can machine learning contribute to mining kepler data? |
exoplanetary discoveries in the past two decades have unveiled an astonishing diversity in the physical characteristics of exoplanetary systems. exoplanets known today range from gas-giants to nearly earth-size planets, and some even in the habitable zones of their host stars. recent advances in exoplanet observations and theoretical methods are now leading to unprecedented constraints on the physicochemical properties of exoplanetary atmospheres. in this work, we briefly discuss some of the key developments in our understanding of radiative processes in exoplanetary atmospheres. we focus on two areas of relevance to the present conference. firstly, we review progress in the understanding of thermal inversions in irradiated giant exoplanets. secondly, we briefly review progress in self-consistent modeling of exoplanetary atmospheres. both these areas benefitted from pioneering contributions of ivan hubeny to whom this conference is dedicated. | exoplanetary atmospheres: thermal inversions and self-consistent models |
two decades ago, technological advancement aligned with some of mankind's oldest and most compelling questions to give birth to exoplanet science. since then, the study of exoplanets, more than any other field of astrophysics, has grown in direct consonance with new instrumentation. in this dissertation talk i will discuss the development of three precision spectrographs that are pushing the limits on current radial velocity (rv) precision: (a) paras, a workhorse optical instrument achieving ~1m/s over several months, (b) the habitable zone planet finder, an upcoming nir instrument for the 10m hobby eberly telescope, and (c) neid, an extreme precision instrument that will be the centerpiece of the nasa-nsf exoplanet observational research (nn-explore) partnership. the path to the extreme precisions required to detect earth analogs (~10cm/s), requires severe technical artistry and demands unprecedented performance from both hardware and software. i will summarize the most challenging sources of measurement error and the hardware solutions we have innovated, including my work on the invention of an efficient ball lens double scrambler (patent pending) that essentially retires issues of illumination instability. as software architect of these instruments, i will also describe the pathways to extreme precision data analysis pipelines, rooted firmly in the heritage of current instruments in the field. fortunately, the scientific return from these meticulously produced spectra will be manifold, extending beyond precision rvs. i will briefly discuss my work leveraging the stability and resolution of similar instruments for stellar activity diagnosis and the determination of insidious false positives, as well as for the direct detection of reflected light from exoplanets. these efforts together underline both the formidable demands and rich rewards of extreme precision spectroscopy, which remains our fundamental tool for the discovery of potentially habitable non-transiting worlds, and may be the best method for identifying targets for future flagship direct imaging missions like habex and luvoir. | the promise of many worlds: detection and characterization of exoplanets with extreme precision spectroscopy |
introduction: the search for life on distant exoplanets is expected to rely on atmospheric biosignatures detection, such as oxygen of biological origin. however, it is not demonstrated how much oxygenic photosynthesis, which on earth depends on visible light, could work under spectral conditions simulating exoplanets orbiting the habitable zone of m-dwarf stars, which have low light emission in the visible and high light emission in the far-red/near-infrared. by utilizing cyanobacteria, the first organisms to evolve oxygenic photosynthesis on our planet, and a starlight simulator capable of accurately reproducing the emission spectrum of an m-dwarf in the range 350-900 nm, we could answer this question. methods: we performed experiments with the cyanobacterium chlorogloeopsis fritschii pcc6912, capable of far-red light photoacclimation (farlip), which allows the strain to harvest far-red in addition to visible light for photosynthesis, and synechocystis sp. pcc6803, a species unable to perform this photoacclimation, comparing their responses when exposed to three simulated light spectra: m-dwarf, solar and far-red. we analysed growth and photosynthetic acclimation features in terms of pigment composition and photosystems organization. finally, we determined the oxygen production of the strains directly exposed to the different spectra. results: both cyanobacteria were shown to grow and photosynthesize similarly under m-dwarf and solar light conditions: synechocystis sp. by utilizing the few photons in the visible, c. fritschii by harvesting both visible and far-red light, activating the farlip response. | oxygenic photosynthetic responses of cyanobacteria exposed under an m-dwarf starlight simulator: implications for exoplanet's habitability |
context: most stars in the galactic stellar population are low-mass stars. very low-mass (vlm) stars are a subset of the low-mass stars typically defined in terms of the stellar masses ranging from 0.6 m_sun to the hydrogen-burning limit of about 0.075 m_sun. aim: the observational studies of vlm binaries can provide effective diagnostics for testing the vlm formation scenarios. the small size of vlms makes them suitable candidates to detect planets around them in the habitable zone. methods: in this work, using the high-resolution near-infrared adaptive optics imaging from the naco instrument installed on the very large telescope, we report the discovery of a new binary companion to the m-dwarf lp 1033-31 and also confirm the binarity of lp 877-72. we have characterized both stellar systems and estimated the properties of their individual components. results and conclusions: we have found that lp 1033-31 ab with the spectral type of m4.5+m4.5 has a projected separation of 6.7+/-1.3 au. on the other hand, with the spectral type of m1+m4, the projected separation of lp 877-72 ab is estimated to be 45.8+/-0.3 au. we further investigated the masses, surface gravity, radii, and effective temperature of the detected components. the orbital period of lp 1033-31 and lp 877-72 systems are estimated to be ~28 and ~349 yr, respectively. our analysis suggests that there is a possibility of finding up to `two' exoplanets around lp 877-72 b. in contrast, the maximum probabilities of hosting exoplanets around lp 877-72 a, lp 1033-31 a, and lp 1033-31 b are estimated to be only ~50%. | investigation of very low mass binaries using vlt/naco |
terrestrial planets in the habitable zone (hereafter hz) around nearby stars are of great interest and provide a good sample to characterize their habitability. in this paper, we collect a nearby star catalog within 20 pc according to the gaia catalog of nearby stars, complete the physical parameters of the stars, and select stars that are not brown or white dwarfs. after selection, a sample of 2234 main-sequence stars is used to estimate the extended hz. then we inject earth-like planets into the extended hz around each star and calculate the signals with four methods, i.e., velocity amplitude for radial velocity, transit probability and depth for transit, stellar displacements for astrometry, and contrast and angular separation for imaging. considering a typical noise model based on classic instruments, e.g., espresso, kepler, gaia, habex, and life, we predict the highest possible detection number of earth-like planets via different methods in the best-case hypothetical scenario. according to this, we conclude that both astrometry and imaging have the potential to detect nearby earth-like planets around g-type stars, while radial velocity has the potential to detect 2% of nearby earth-like planets around m stars with a precision of 0.2 m s-1. our work also provides the precision requirements for future missions to reveal the nearby earth-like planet in the hz. | the potential of detecting nearby terrestrial planets in the hz with different methods |
our understanding about the heliosphere dramatically evolved from the results from voyager, cassini and interstellar boundary explorer (ibex). with the rapid discovery of exoplanets in other stellar systems it is important to understand how this new acquired knowledge affects the astrospheres around other stars. in particular, recently the shape of the heliosphere is being challenged by theoretical and observation work (opher et al. 2015; diyalinas et al. 2017). the nearest star to the sun, proxima centauri, is particularly interesting as it was recently discovered to host an earth-size planet in its "habitable zone", proxima b. here we investigate the astrosphere around proxima centauri. as the star moves through the surrounding partially-ionized medium, neutral hydrogen atoms penetrate the astrospheres and through charge-exchange with the supersonic stellar wind creating a population of hot pick-up ions (puis). we present global magnetohydrodynamic simulations that treats the puis as a separate fluid. most global models treat the pui and thermal component as a single fluid. planetary atmospheres are affected by particle fluxes from their host stars. the only means by which coronal winds of sun-like stars have ever been probed is by the circumstellar h lyman-alpha absorption fin the interaction region between the wind and the interstellar medium, namely the "astrospheres". the lyman-alpha constrains on the stellar wind based on hubble space telescope measurements rely on prior hydrodynamical models. here we revisit the constraints on the mass-loss of proxima centauri (wood et al. 2011) with improved theoretical predictions and discuss the implications for space weather effects on proxima b. | the astrosphere and mass-loss ratio of proxima centauri |
to understand the uniqueness of our solar system, we must assess the system architectures and demographic features existing in the known planet population, but such a task requires a homogeneous set of candidates. fortunately, the kepler spacecraft continuously collected photometry from a single patch of the sky, which in turn produced a well characterized catalog of transiting exoplanets. however, previous studies assumed multi-planet systems were subject to the same selection effects as their single-planet counterparts. i investigate this assumption, finding that a proper completeness accounting significantly increases the underlying occurrence of multi-planet systems to 5.86 planets per fgk dwarf and only requires a 1.5 degree average system mutual inclination. using this correction i provide an updated extrapolation of the occurrence of earth analogs and find that 5.9% of gk dwarfs have more than one planet within their habitable zone. additionally, the k2 mission collected photometry from 18 fields along the ecliptic plane, providing a unique opportunity to understand how exoplanet formation may be affected by galactic latitude, stellar metallicity, and stellar age. for my thesis, i developed a fully automated pipeline able to detect and vet transit signals in k2 photometry, enabling assessment of sample completeness and reliability. this catalog contains 768 planets, with 235 newly identified candidates. correspondingly, i present the first uniform analysis of small transiting exoplanet occurrence outside of the kepler field, finding a metallicity dependence in small planet occurrence. i also discuss how the sun's late stage evolution and the existing solar system architecture will capture jupiter and saturn into a mean-motion resonance. eventually perturbations from passing stars will trigger large-scale instability, culminating in the disassociation of all outer planets. extrapolating this result to other systems indicates a temporal dependence on bound planet occurrence in the galaxy. | utilizing kepler and k2 to advance exoplanet demographics |
the search for habitable exoplanets received new momentum with recent discoveries of tens of exoplanets in habitable zones around cool stars. many of host stars are represented by active m dwarfs and young g and k dwarfs generating intense x-ray and extreme uv (xuv) radiation fluxes from their quiescent coronae and intense and frequent flares. this suggests that many of rocky exoplanets are exposed to large fluxes (100-300) of stellar xuv radiation that are by a factor of 30-300 greater than that received by our planet today. the stellar xuv fluxes ionize and heat the upper atmospheres of exoplanets, driving significant atmospheric escape via hydrodynamic escape of both ions and neutrals. here, we present the results of application of the one-dimensional (1-d) global ionosphere thermosphere model (gitm) to an earth-like planet exposed to 1, 10 and 60 times xuv fluxes of the current earth. the results suggest the upper atmospheric mass loss is dominated by oxygen and nitrogen ion escape between xuv fluxes of 1-10 xuvearth, while the planetary atmosphere transitions to a hydrodynamic escape state at the xuv flux of ~60 xuvearth. we present the thermodynamic atmospheric parameters and total atmospheric escape rates for unmagnetized and magnetized earth-like planets for parameter regimes relevant to the ongoing search for spectral signatures of escape processes that could impact the atmospheric evolution of rocky planets and their potential habitability. | modeling x-ray and euv driven hydrodynamics escape from earth-like (magnetized and unmagnetized) exoplanets with exo-gitm |
from life on other planets to virtual classrooms this thesis spans a wide array of research topics all based on how we see other worlds. our understanding of everything from moon phases, the planets in our solar system, and exoplanet atmospheres come from our interpretation of light and one day, our knowledge of light will be used as evidence for the discovery of life on another planet. in the time before we scattered rovers, landers, and brave souls across the solar system we only knew of the planets and moons from the light they reflected from the sun back to us. we are in much the same situation with exoplanets today. our telescopes can gather the light from distant worlds but they are too far out of reach to confirm our observations with in-situ measurements. soon we will be able to gather light from even smaller exoplanets and eventually earth-sized exoplanets orbiting in their star's habitable zone. as a reference guide to these upcoming observations what better place to compare to than our own solar system. what we've done is take measurements of planets in our own solar system and treat them as exoplanets to determine how different surface types can be differentiated. the result is a database of the spectra, geometric albedos, and color of 19 solar system objects for use as an exoplanetary field guide. a step beyond the field guide is a way to explore worlds only physics and our imaginations are limited by. by using computer models, we can create thousands of planets to determine the physical and chemical stability of any environment. one parameter domain of interest is the role of surface color on a planet's habitability. different materials have unique thermal properties that either cool or heat a surface depending on their color and the light that hits them. dark oceans absorb light well and heat up while white sand is highly reflective and keeps cool... | the color of habitability |
most of current hypotheses, place the origin of life on earth in an aquatic habitat. therefore, celestial bodies of an oceanic nature, such as enceladus, europa, or certain exoplanets, become important objects of study when searching for inhabited worlds. esa (european space agency) has recently launched the juice mission (jupiter icy moons explorer), and its expected data will help us evaluate their habitability conditions. in the meantime, studies on extreme habitats at earth must be conducted. among the most changing ecosystems are the intertidal and subtidal zones, where situations of overheating, ultraviolet irradiation, and desiccation are common. in this demanding habitat, marine tardigrades thrive. tardigrades, also known as water bears, are well known for their excellent polyextremophilic behaviour and stress resistance ubiquitously. although tardigrades have been studied in a wide variety of habitats, our knowledge remains limited when it comes to marine populations and there is where our study emphasizes. we collected several samples of lichina pygmaea and macroalgae of the genus ulva, at portiño beach (galicia, nw spain). different treatments were applied to maximize the living collection of tardigrades and three genera were identified: echiniscoides, styraconyx, and batillipes. juvenile and adult individuals were distinguished, and morphological differences were also observed between females and males. various tests of feeding and substrate adhesion were initiated to attempt long-term culturing under laboratory conditions for echiniscoides and batillipes in particular. out of our study, we will present here the results obtained so far on the observed life cycles, molting or encystment, together with some experimental results of the exposure of desiccated lichina to gamma ray irradiation. we aim to contribute to the study of the resistance of marine tardigrades as useful extra-terrestrial habitability models, in connection with solar system bodies and oceanic exoplanets. our outcome is discussed in the light of recent literature findings in the field. we acknowledge support from public state employment service (sepe) and university of vigo, under contract e-36-2023-0072917 | marine tardigrades as a model of extraterrestrial habitability: an astrobiological study at the university of vigo |
two decades ago, technological advancement aligned with some of mankind’s oldest and most compelling questions to give birth to exoplanet science. since then, the study of exoplanets, more than any other field of astrophysics, has grown in direct consonance with new instrumentation. building on the success of instruments like harps, doppler velocimetry is now firmly on the path towards extreme precisions (∼10 cm/s), driven by the urge to find true earth analogs. this effort, however, requires severe technical artistry and demands unprecedented performance from both hardware and software. in this dissertation, i present the comprehensive and multifaceted path to extreme precision spectroscopy. we begin with existing spectrographs and the battlefield lessons they offer, focusing particularly on paras, an operating workhorse instrument with which i have been deeply involved, achieving ∼1 m/s radial velocity (rv) precision over several months. i then detail the design and development of two new instruments that will achieve unprecedented rv precisions: (a) the habitable zone planet finder, an upcoming near-infrared instrument for the 10 m hobby eberly telescope, designed to achieve 1-3 m/s on cool stars, and (b) neid, an extreme precision optical instrument aiming at < 30 cm/s that will be the centerpiece of the nasa-nsf exoplanet observational research (nn-explore) partnership. i summarize the most challenging sources of measurement error and the hardware solutions we have created, including my work on the invention of an efficient ball lens double scrambler that essentially retires issues of illumination instability. as software architect of these instruments, i also describe the pathways to extreme precision data analysis pipelines, rooted firmly in the heritage of current instruments in the field. having ensured the exquisite quality of spectra from these instruments, i investigate the presence of insidious false positives that mimic the signatures of exoplanets, and the use of complementary techniques for further vetting of promising candidates. lastly, i present the long arc towards the future of this field, including the direct detection of planetary photons that will light the way towards our understanding of universal habitability. | connecting the pale blue dots: detection & characterization of exoplanets with extreme precision spectroscopy |
understanding the divergent evolution of venus and earth is a fundamental problem in planetary science. although venus today has a hot, dry atmosphere, recent modeling suggests that venus may have had a clement surface with liquid water until less than 1 billion years ago [1]. venus today has a nearly stagnant lithosphere. however, ishtar terra"s folded mountain belts, 8-11 km high, morphologically resemble tibet and the himalaya mountains on earth and apparently require several thousand kilometers of surface motion at some time in venus"s past. loss of liquid surface water increases the coefficient of friction in fault zones, favoring a transition from an early mobile lithosphere to a present-day stagnant lithosphere [2]. solar-driven climate evolution could contribute to a prolonged epoch of water loss on venus and may be the ultimate cause of the divergent evolution of both the climate history and the interior dynamics of venus and earth. in addition to being a problem of first-order importance for solar system evolution, understanding the divergent evolution of venus and earth is also important for understanding the temporal and spatial distribution of habitable environments in the solar system. understanding the evolution of venus is also a key test for models that interpret earth-sized exoplanets. testing evolutionary hypotheses requires interpreting clues that were left behind in both the isotopic composition of the venus atmosphere and in the rock record of the venus surface. although several mission concepts are currently competing for possible flights to venus, only the deep atmosphere venus investigation of noble gases, chemistry, and imaging plus (davinci+) mission [3] can examine both the atmospheric isotopic record and the rock record of venus. davinci+ is therefore a compelling choice for selection in the current nasa discovery program phase a competition. davinci+ includes an atmospheric entry probe and a carrier spacecraft (figure 1). the probe measures atmospheric composition using a mass spectrometer and tunable laser spectrometer, performs descent imaging, and measures atmospheric structure. following completion of the probe mission, the carrier spacecraft enters venus orbit and images the venus surface in the 1 micron atmospheric window. this payload is ideally suited for testing models of venus evolution. figure 1: the davinci+ entry probe studies the atmosphere while imaging the alpha regio landing site. afterward, the carrier probe performs infrared imaging of selected targets from orbit. the history of water: isotopic record pioneer venus measured the d/h value of an h2so4 cloud droplet at ~55 km as 157±30 times the terrestrial value, which was interpreted as the signature of escape of water from the venus atmosphere [4]. terrestrial spectroscopy produced a similar range, whereas venus express measured a value up to three times larger between 70-90 km [5]. the large value relative to earth shows that venus lost a substantial amount of water, but the large uncertainty and the lack of data below the clouds makes it difficult to quantitatively model the history of water loss [6]. davinci+ will measure d/h to high precision from above the clouds down to the surface, greatly improving our ability to interpret the history of water loss on venus. in addition, the abundance and isotopic ratios of xe and kr, together with the kr/ar and xe/ar ratios, which davinci+ will measure with high precision, will be instrumental in revealing whether venus and earth formed in the same way and how their climates diverged. the history of water: rock record a key but poorly answered question is the extent to which venus has produced granitic or felsic (sio2-rich) volcanism. small amounts of felsic magma can be generated by lithospheric processes [7], but large amounts of felsic material requires the presence of water in the melting zone [8], as in terrestrial subduction zones. tessera, which are regions of old, thick, highly tectonized crust, are widely accepted as the most likely location for felsic material on venus. venus express observations suggest that tessera in alpha regio has a felsic composition [9]. davinci+ will explore the presence and distribution of felsic rock in two ways. comparison of the reflectivity at 1 micron and in panchromatic descent images at the alpha regio landing site will test the presence of felsic rock at patch sizes much smaller than can be observed from orbit. descent imaging will also explore the landing zone geomorphology, and stereo topography will enable quantitative modelling of faulting and folding. orbital imaging in the 1 micron atmospheric window will test for the presence of felsic rock in other tessera, including tellus regio, fortuna tessera, maxwell montes, ovda regio, and thetis regio. our approach is similar to virtis on venus express [9] but focuses on regions in the northern hemisphere and near the equator that were not imaged by virtis. the history of volcanism: isotopic record volcanic outgassing releases radioactive decay products such as 40ar and 4he to the atmosphere. davinci+ measurements of their atmospheric abundance can be used to estimate volcanic outgassing over time. 40ar provides an integrated record of volcanism over venus history. because 4he escapes from the atmosphere to space, its atmospheric abundance constrains geologically recent (last billion years) volcanism. existing measurements of 40ar and 4he are too imprecise to strongly constrain the volcanic history of venus [10] but will be measured with much greater accuracy by davinci+. because davinci+ will constrain the history of both water and volcanism on venus, it will provide new insights into the feedbacks that shaped the divergent evolution of venus and earth. references [1] way and del genio, jgr 125, e2019je006276, 2020. [2] weller and kiefer, jgr 125, e2019je005960, 2020. [3] garvin et al., lpsc 51, abstract 2599, 2020. [4] donahue et al., science 216, 630-633, 1982. [5] bertaux et al., nature 450, 646-649, 2007. [6] donahue et al., venus ii, 385-414, 1997. [7] elkins-tanton et al., jgr 112, e04s06, 2007. [8] campbell and taylor, grl 10, 1061-1064, 1983. [9] gilmore et al., icarus 254, 350-361, 2015. [10] namiki and solomon, jgr 103, 3655-3677, 1998. | venus, earth's divergent twin?: testing evolutionary models for venus with the davinci+ mission |
with the launch of the james webb space telescope (jwst) in the early 2020s, astronomers will likely have the sensitivity to peer into earth-size planet atmospheres, particularly for exoplanets orbiting the smallest of stars, such as the seven planets transiting trappist-1. these observations will have the potential to detect terrestrial atmospheres, and begin to characterize their composition, constrain habitability, and search for biosignatures. we report optimal strategies for investigating the nature of the trappist-1 planet atmospheres with jwst, present testable hypotheses for discriminating between planets that have experienced ocean loss and those that may be habitable, and develop novel approaches for retrieving terrestrial atmospheric constraints in the era of jwst. although jwst will likely break new ground for terrestrial exoplanet comparative planetology, its capacity to detect signs of habitability and biosignatures will be limited by a lack of sensitivity to the lower atmospheres of potentially habitable planets — which confounds our ability to definitively detect surface oceans, and will be restricted to only planets transiting nearby late m dwarfs — which have several significant challenges to habitability not experienced by planets orbing more sun-like stars. these practical considerations help to motivate the need for a large aperture, space-based, direct-imaging telescope, such as luvoir or habex, that can observe reflected-light spectra and time-series light curves of earth-like exoplanets orbiting sun-like stars. we demonstrate how such a future telescope would have the capability to directly detect habitability using observations of ocean glint at crescent phase, and perform a robust search for biosignature gases in the spectra of dozens of earth-like planets orbiting in the habitable zones of sun-like stars. | the detection and characterization of terrestrial exoplanet atmospheres and the search for habitability and biosignatures |
land is required not only to provide life a stable surface but also to support a stable carbonate-silicate cycle. modeling studies have surmised that land planets may support a wider and longer continuous habitable zone than aqua planets, both at the moist greenhouse limit and at the outer edge. the habitability of a planet is not well characterized by its mean state but by its diversity of climate regimes that distribute heat and water, if present, over its surface heterogeneously, producing environmental niches that will differ in suitability for life. a planet's climate is subject to the interaction of many planetary features that affect its circulation patterns including: parent star, orbital dynamics, atmospheric composition, surface composition. given such a diverse parameter space, if a habitable planet harbors water, how might it distribute over the planet and where will the liquid water be for life? because most exoplanet climate modeling studies thus far have biased the literature sampling of the parameter space to aqua planets, earth continents, the sun, m stars, and extremes of atmospheric co2 content, in this study we filled the gaps through a perturbed parameter ensemble (ppe) in the nasa resolving orbital and climate keys of earth and extraterrestrial environments with dynamics general circulation model (rocke-3d gcm). we simulated the climates of idealized planets that are all land with flat topography. we conducted a latin hypercube sampling from the following ten variables in 110 experiments: stellar temperature and spectra from observed g, k, and m stars; irradiance spanning from that of trappist1-e to early venus; rotation period including tidally locked, 3:2 spin-orbit, and 1-128 earth days; obliquity from 0 to 90°; surface pressure from 0.5-10 bar; co2 content (in n2/co2 atmospheres) from 0 to 10 bar; surface albedo 0.11-0.3; surface roughness from the gcm minimum of 0.005 to 0.7, the average of bare soils on earth; two soil textures having water holding capacity at the minimum, sand, and optimum for life, silt loam; and initial soil water content spanning the field capacities of the two soil textures, which give 0.008-0.026% of the earth's ocean. thus, these were fairly dry planets, but with water free to circulate and accumulate in different climate zones and in the atmosphere. we evaluated the planets' "climatological period" to quantify mean climate states and, through multivariate statistical analysis, identify continuous, non-linear relations between the parameters and several metrics of habitability, including surface water cover, aridity, soil relative extractable water, and the planetary water phase budget. from these we derived classifications of rocky land planet climatologies, such as eyeball, billiard ball, and fabergé egg planets. we identified parameter thresholds for transitions to slushball, clement, and steam planet states. 80% of the variance in surface temperature may be explained by stellar type, irradiance, and greenhouse gas content, with the solar day length, surface pressure, and obliquity only weakly significant. available liquid water for life by mass and areal extent are then correlated with temperature, with obliquity up to about 60° weakly promoting surface wetness. we look for surface water metric relationships to those parameters and climate features that might be observed by exoplanet missions, including stellar type, irradiance, planetary albedo, cloud cover, and upper atmosphere water vapor. this framework offers a modeled context to quantify the uncertainty in habitability given many parameters that cannot be observed. this ensemble of idealized land planets lays foundations for further filling the parameter space with more diverse specifications of the planet size, and compositions of the surface and atmosphere for understanding the climatologies of land planets in particular. | land planets in a rocke-3d gcm perturbed parameter ensemble: fractional habitability |
which habitable-zone planets can actually support life? a recent study uses a nearby planet proxima centauri b to examine how the presence and size of a land mass impacts the habitability of an ocean world.a target for potential lifein our galaxy, roughly 80% of stars are cool, dim m dwarfs and one in six of these is thought to host an earth-sized planet in its habitable zone. but being in a stars habitable zone doesnt guarantee a planets habitability! m-dwarf habitable-zone planets present valuable targets for observations and models to better understand which of these worlds can support life.artists impression of a cold, tidally-locked planet. ice covers much of the planets surface, but the point directly facing the planets host star remains ice-free. [nasa/jpl-caltech]most habitable-zone planets around m dwarfs are likely tidally locked: one side of the planet experiences constant day; the other, constant night. nominally, this would cause only one region of the planet to be heated the point closest to the star and the rest of the planet would be locked in darkness and ice. but if the planet is covered in a dynamic ocean, heat can be transported around the planet via ocean currents, affecting the potential habitability of the world.do continents get in the way of this heat transport? and how do land masses affect the circulation of nutrients in the ocean, critical for sustaining ocean-based photosynthetic life? a new study explores the particular case of a tidally locked ocean planet with a continent and it uses the nearby proxima centauri b as a model to do so.modeling a nearby worldat just 4.2 light-years away, proxima b is the closest known exoplanet and presents an excellent target for future follow-up observations. this habitable-zone m-dwarf planet is probably tidally locked, and estimates of its density have led to speculation that the planet is covered in a large ocean.ocean heat transport in the authors models for varying continent size; from top to bottom, continents (noted as the white rectangle in the figure) cover 0%, 4%, 22%, and 39% of the planet surface. continents at the substellar point inhibit ocean heat transport. [adapted from salazar et al. 2020]in a recent publication led by andrea salazar, a team of scientists from the university of chicago has used a general circulation model to explore how heat and nutrients are transported on an ocean-covered, tidally locked proxima b both with and without the presence of a land mass in the ocean.salazar and collaborators placed a continent at the point on the planet closest to the star because land masses are thought to migrate to the planetstar axis over time and tested a range of continent sizes, covering from 0 to 40% of the total planet surface.promising outcomesthe authors find that the presence of a continent decreases how efficiently heat and nutrients are transported from the dayside to the nightside of the planet the larger the continent, the less efficient the transport. nonetheless, in all cases, an ice-free ocean is maintained on the planetary dayside, and nutrients are circulated and delivered to the layer of the ocean where photosynthesis is viable, providing ideal conditions for photosynthetic marine life.this work suggests that the presence of both a dynamic ocean and continents wont decrease the habitability prospects of tidally locked planets like proxima b. this is good news as we prepare for future observations with the james webb space telescope, which may provide further insight into this nearby, potentially habitable world and others like it.citationthe effect of substellar continent size on ocean dynamics of proxima centauri b, andrea m. salazar et al 2020 apjl 896 l16. doi:10.3847/2041-8213/ab94c1 | the impact of land on an ocean world's habitability |
future exoplanet direct imaging missions, such as habex and luvoir, will select target stars to maximize the number of earth-like exoplanets that can have their atmospheric compositions characterized. because one of these missions' aims is to detect biosignatures, they should also consider the expected biosignature yield of planets around these stars. in this work, we develop a method of computing relative biosignature yields among potential target stars, given a model of habitability and biosignature genesis, and using a star's habitability history. as an illustration and first application of this method, we use mesa stellar models to calculate the time evolution of the habitable zone, and examine three simple models for biosignature genesis to calculate the relative biosignature yield for different stars. we find that the relative merits of k stars versus f stars depend sensitively on model choice. in particular, use of the present-day habitable zone as a proxy for biosignature detectability favors young, luminous stars lacking the potential for long-term habitability. biosignature yields are also sensitive to whether life can arise on cold start exoplanets that enter the habitable zone after formation, an open question deserving of more attention. using the case study of biosignature yields calculated for theta cygni and 55 cancri, we find that robust mission design and target selection for habex and luvoir depends on: choosing a specific model of biosignature appearance with time; the terrestrial planet occurrence rate as a function of orbital separation; precise knowledge of stellar properties; and accurate stellar evolutionary histories. | a framework for relative biosignature yields from future direct imaging missions |
we report the discovery of three exoplanets transiting toi-4010 (tic-352682207), a metal-rich k dwarf observed by tess in sectors 24, 25, and 52. we confirm these planets with harps-n radial velocity observations and measure their masses with 14-21% precision. toi-4010 b is a sub-neptune (p = 1.3 days, rp = 3.1 r⊕, mp = 8.7 m⊕) in the hot neptune desert, and is one of the few such planets with known companions. meanwhile, toi-4010 c (p = 5.4 days, rp = 5.9 r⊕, mp = 21.6 m⊕) and toi-4010 d (p = 14.7 days, rp = 6.1 r⊕, mp = 33.3 m⊕) are similarly-sized sub-saturns in short-period orbits. toi-4010 c and d are among the most massive sub-saturns to be discovered in systems of multiple planets with short periods, and the most massive planets among similar systems with multiple sub-saturns. radial velocity observations also reveal a potential super-jupiter-mass planet companion in a long-period, eccentric orbit (p ~ 552 days, e ~ 0.2), placing it in the habitable zone. toi-4010 has no known analogs, and is one of the few systems with multiple short-period gas giants to be discovered so far. | three short-period large exoplanets with a long-period super-jupiter companion orbiting toi-4010 |
photochemical hazes are expected to form and significantly contribute to the chemical and radiative balance of exoplanets with relatively moderate temperatures, possibly in the habitable zone of their host star. in the presence of humidity, haze particles might thus serve as cloud condensation nuclei and trigger the formation of water droplets. in the present work, we are interested in the chemical impact of such a close interaction between photochemical hazes and humidity on the organic content composing the hazes and on the capacity to generate organic molecules with high prebiotic potential. for this purpose, we explore experimentally the sweet spot by combining n-dominated super-earth exoplanets in agreement with titan's rich organic photochemistry and humid conditions expected for exoplanets in habitable zones. a logarithmic increase with time is observed for the relative abundance of oxygenated species, with o-containing molecules dominating after 1 month only. the rapidity of the process suggests that the humid evolution of n-rich organic haze provides an efficient source of molecules with high prebiotic potential. | humid evolution of haze in the atmosphere of super-earths in the habitable zone |
the kepler mission provided groundbreaking insight into the field of exoplanet demographics. yet our understanding of the kepler sample has evolved over time following development of statistical techniques and updated catalogs. gaia-revised stellar parameters revealed that most stars (and their planets) are larger and hotter than previously believed (berger et al. 2020), bringing into question previous results that could not have incorporated such changes. this includes seminal studies of kepler's m dwarf stars and their demographic trends with stellar mass, and their occurrence of earth-sized habitable zone planets. refining the latter is especially relevant for both current and future missions seeking to detect such worlds. we present an updated investigation into kepler's sample of earth-sized planets orbiting m dwarf stars, incorporating modern parameters and statistical considerations. because there are now few detections of earth-sized planets at low instellations, we developed a set of forward models to predict an occurrence rate of 8.58+17.94-8.22% for earth-sized planets in the conservative habitable zone. this result is consistent with previous estimates (dressing & charbonneau 2015, hsu et al. 2020) but notably more uncertain, placing limits on the statistical power of the updated kepler sample. when comparing with similarly comprehensive studies of sun-like stars (kunimoto & matthews 2020, bergsten et al. 2022), we found that earth-sized habitable zone planets are just as common around m dwarfs as they are around fgks. we also find consistent occurrence rates between our predominantly early m dwarf sample and that of mid-to-late m dwarfs (ment & charbonneau 2023). this directly impacts how the population of small planets varies with stellar mass, which is important for our understanding of rocky planet formation and the ongoing search for exo-earths. | the occurrence of earth-sized planets around m dwarf stars |
the recent discovery of seven earth-sized, terrestrial planets around an m dwarf star was met with excitement and optimism. but how habitable are these planets actually likely to be? a recent study of these planets likely climates may provide an answer to this question.an optimistic outlookin february of this year, the trappist-1 system was announced: seven roughly earth-sized, transiting, terrestrial planets all orbiting their host ultracool dwarf star within a distance the size of mercurys orbit. three of the planets were initially declared to be in the stars habitable zone and scientists speculated that even those outside the habitable zone could potentially still harbor liquid water making the system especially exciting.in wolfs simulations, the surface temperature (solid lines) of trappist-1d grows to more than 380k in just 40 years. [adapted from wolf 2017]the planets were labeled as temperate because all seven have equilibrium temperatures that are under 400k. since liquid water requires a surface temperature of 273-373k, this certainly seems promising!finding realistic temperaturesbut theres a catch: equilibrium temperatures are not actual measurements of the planets surface temperature, theyre just very rudimentary estimates based on how much light the planet receives. to get a better estimate of the real temperature of the planet and therefore assess its habitability you need advanced climate modeling of the planet that include factors like the greenhouse effect and planetary albedo.in wolfs simulations, the surface temperature of trappist-1f plummets rapidly even when modeled with dense carbon dioxide atmosphere (purple line). the bottom panel shows the corresponding rapid growth of sea-ice on the surface oceans for the different atmospheric models. [wolf 2017]to that end, scientist eric wolf (university of colorado boulder) has conducted state-of-the-art 3d climate calculations for the three center-most planets planets d, e, and f in the trappist-1 system. wolf assumed traditional terrestrial-planet atmospheres composed of nitrogen, carbon dioxide, and water, and he examined what would happen if these planets had large water supplies in the form of surface oceans.runaway and snowball planetswolfs climate model indicates that the closest-in of the three planets, planet d, would undergo thermal runaway even in the best case scenario. in just 40 years of the simulation, the planets surface temperature exceeds 380k, suggesting it couldnt continue to sustain liquid water. wolf argues that planet d and the two planets interior to it, b and c, all lie inside of the traditional liquid water habitable zone they are hot, dry, and uninhabitable.next, wolf models the outermost of the three center planets, planet f. even when planet f is modeled with a dense carbon dioxide atmosphere, it cant avoid its fate of becoming completely ice-covered within roughly 60 years. wolf concludes that planets f, g and h all lie outside of the traditional habitable zone defined by the maximum carbon dioxide greenhouse limit.equilibrium solutions for trappist-1e with various atmospheric conditions. top panel: mean surface temperature. middle panel: sea-ice coverage. bottom panel: habitable surface area. [wolf 2017]goldilocks?lastly, wolf turns to planet e, the central planet in the system. this planet, he finds, is the most viable candidate for a robustly habitable world. the simulations show that planet e can maintain habitable surface conditions for a variety of atmospheric compositions.while astrobiologists eyeing trappist-1 may be disappointed that at second glance the planets are not quite as inhabitable as they first seemed, it is promising to see that the habitability of the central planet holds up reasonably well to some more realistic testing. either way, future examinations of all seven of these planets should help us learn more about terrestrial, earth-sized planets.citationeric t. wolf 2017 apjl 839 l1. doi:10.3847/2041-8213/aa693a | habitability of the trappist-1 system |
exoplanets are planets that orbit stars outside of our solar system. an array of diverse exoplanets have been discovered around many stars. this project aims to evaluate the potential habitability of our hypothetical exoplanet ut-0a70. our hypothetical planet has characteristics reminiscent of both earth and mars in the sense that it has large land masses, is rich in oxidized iron, and contains hyper saline oceans. the planet has no known seasons as the planet has an axis tilt of 8 degrees. the planet will prove difficult to be hospitable for humans due to the carbon dioxide rich atmosphere and the fact that the atmosphere is about half the density of earth's. we plan to make the planet habitable by paraterraforming around the equator of the planet so that life will reside in sustainable temperature zones. we also plan to address the issue of water quality by installing filtration devices that will make the water sustainable for both humans and plants. since plants thrive in iron-rich soil and benefit from the carbon dioxide in the atmosphere, we believe that significant and beneficial plant life will be sustainable with adjustments to the water. another benefit for plant life is the duration of the day. since the length of a day on planet ut-0a70 is approximately twice the length of a day on earth, the plants will have ample amount of sunlight to sustain themselves. exploring our planet has added benefits because our economic geologist has hypothesized that due to the previous ancient volcanic activity, we will find precious metals such as gold and iron in volcanic regions around the planet. a rover can be sent to extract these resources and bring them back to earth where they can then be used as material for the duration of the mission. for example, the gold could be used for the space suits needed to access our planet, and the iron can be used as material for the paraterraforming structural designs since these important resources are rapidly depleting on earth, ut-0a70 can serve as a vital replenishment for our scarcity on earth; as well as providing an adequate terrain for paraterraforming experiments. | paraterraforming hypothetical exoplanet ut-0a70 |
mauve is a small space mission by blue skies space mainly dedicated to investigating the stellar magnetism of active stars (across a broad spectral range from f- to m-type stars). this concept is particularly of interest in the context of stellar systems hosting exoplanets, where the magnetic activity of the host star can substantially impact the atmosphere of exoplanets located within their habitability zone. mauve offers a broad wavelength range from nuv to vis (200-700 nm, r~30-100), and will monitor 1000+ k- and m-dwarfs (ranging from less than an hour to long-term monitoring depending on the targets' coordinates). this category of stars not only includes the best candidates for discovering exoplanets (due to their unique features), but also comprises the prime exoplanetary host candidates harboring life. k- and m-dwarfs are particularly active stars and flare frequently, which in turn can either erode exoplanetary atmospheres, or intrigue prebiotic chemistry and initiate life on them. mauve strives to provide the very low resolution spectra of these complex events in uv and vis spectral ranges, and contribute to the previous photometric studies of flares performed by kepler and tess in white light. this unique opportunity thus not only adds a brand new dimension to the studies of flaring stars, but also enables investigating the simultaneous magnetic diagnostics of stars during this transiting phenomenon. | mauve: a uv-vis spectroscopy facility dedicated to studying the magnetic activity of active stars |
the university of colorado led extreme-ultraviolet stellar characterization for atmospheric physics and evolution (escape) small explorer mission concept is designed to measure the extreme- and far-ultraviolet (euv; 80 - 560 a, 600 - 825 a, fuv; 1280 - 1650 a) irradiance and are activity of exoplanet host stars; essential measurements for assessing the stability of rocky planet atmospheres in the liquid-water habitable zone. the escape design consists of a fixed optical configuration with a grazing incidence gregorian, or "hetterick- bowyer", telescope feeding grazing and normal incidence spectroscopic channels. the telescope is provided by a joint nasa marshall space flight center and smithsonian astrophysics observatory team. the grazing incidence gratings have a radial profile and are ruled into single-crystal silicon using electron-beam lithography in the nanofabrication laboratory at pennsylvania state university. normal incidence gratings have aberration correcting holographic solutions and are supplied by horiba jobin yvon. spectra are imaged onto a curved microchannel plate detector supplied by the university of california, berkeley. escape utilizes the ball aerospace bcp spacecraft. the simple, fixed configuration design of escape is projected to exceed the effective area of the last major euv astrophysics spectrograph, euv e-ds/s, by more than a factor of 50, providing unprecedented sensitivity in this essential bandpass for exoplanet host-star characterization. we report on the escape design, projected performance and mission implementation plan, as well as the trade studies carried out over phase a to scope the first nasa euv astrophysics mission in nearly 30 years. if selected, escape will launch in fall 2025. | opto-mechanical design of the escape small explorer: an euv spectrograph for exoplanet host star irradiance and cme activity |
the photometric analysis of sample am stars is carried out to determine the stellar characteristics and to constrain the stellar dynamics. the spectroscopic analysis of the studied am stars confirms their general characteristics of am stars. the available data on elemental abundances for hd 113878 and hd 118660 have shown different characteristics during different epochs of observations. the basic stellar parameters (mass, luminosity, radius, life time, distance, proper-motion, etc.) are also determined to identify the stellar habitat zones for earth like exoplanet. such information is important to identify suitable planets for human settlement in the near future. in this connection, the tidal radius and boundaries of the habitable zone of each star have been computed to support the search of an extra-terrestrial life around them. asteroseismic mass scale test shows greater stellar masses comparable to the solar mass. | photometric and spectroscopic analysis of five am stars |
the closeby habitable exoplanet survey (ches), a proposed space-borne mission to detect earth-like planets orbiting 100 nearby solar-type stars (∼10 pc or approximately 32 light years from the sun) via micro-arcsecond relative astrometry, is currently being considered by the chinese academy of sciences as a possible space mission for future launch (figure 1). the discovery of earth-like planets (or earth twins, planets with an orbit, mass, and environment similar to earth) in the habitable zones around nearby solar-type stars will be another "giant leap for mankind" and help us begin to answer essential scientific questions such as "are we alone in the universe?", "is earth unique?", and "how do planets become the cradle of life?" finding such planets could even enable future human visits and identify new habitable places to live. | ches: an astrometry mission searching for nearby habitable planets |
argusspec will be a fast-response, low-resolution spectroscopic follow-up system. built almost entirely from off-the-shelf components, including a medium-aperture (16-in.) ritchey-chretien telescope, a very-low-noise cmos detector, a low-resolution (r~100) spectrograph, and a fast-slew (50 deg/s) mount, argusspec will begin observations of bright transient events (mv ≤ 13) within tens of seconds of detection. argusspec will use all-sky transient alerts from the evryscope, the argus pathfinder, and the planned full argus array; the latter two systems giving the fastest alerts for optical transients to date. until now, the high-cadence sky has been largely inaccessible for spectroscopy. for example, large flares from active stars have dramatic impacts on orbiting exoplanets, but are difficult targets for spectroscopic follow-up due to their short-timescale evolution. planets in the active stars' habitable zones will be impacted by flares and superflares (energies ≥ 1033 erg), and associated high-energy particle emissions, which could strip the planet of its atmosphere and impart massive amounts of ultraviolet flux; this could be devastating to any life on the planet's surface. there has not been a systematic spectroscopic survey of energetic flaring events across a wide range of stellar masses; almost all large flares observed spectroscopically have been from a small sample of active mid-m stars through staring campaigns. for the first time, argusspec will build a library of superflare spectra from across the night sky, allowing for statistical constraints to be placed on their blackbody evolution and morphology. here we present the design, project status, and science drivers of argusspec. | argusspec: rapid, autonomous spectroscopic follow-up of bright transients |
space borne nulling interferometry in the mid-infrared waveband is one of the most promising techniques for characterizing the atmospheres of extra-solar planets orbiting in the habitable zone of their parent star, and possibly discovering life markers. one of its most difficult challenges is the control of free-flying telescope spacecrafts moving around a central combiner in order to modulating the planet signal, within accuracy better than one micrometer at least. moreover, the whole array must be reconfigured regularly in order to observe different celestial targets, thus increasing the risk of loosing one or more spacecrafts and aborting the mission before its normal end. in this paper is described a simplified optical configuration where the telescopes do not need to be rotated, and the number of necessary array reconfigurations is minimized. it allows efficient modulation of the planet signal, only making use of rotating prisms or mirrors located into the central combiner. in this paper the general principle of a nulling interferometer with a fixed telescope array is explained. mathematical relations are established in order to determining the planet modulation signal. numerical simulations are carried out for three different arrangements of the collecting telescopes. they confirm that nulling interferometry in space does not require a rotating telescope array. | nulling interferometry in space does not require a rotating telescope array |
the warm giants with tess collaboration (wine) is at the forefront of detecting, confirming, and characterizing long-period giant exoplanets from tess. these warm giants provide a key population to constrain planet formation and evolution theories. our systematic search for transits (including single transits) in the tess light curves has given rise to hundreds of transiting giant candidates with periods larger than 10 days, out to hundreds of days. our efficient ground-based radial-velocity and photometric follow-up of the southern skies has already confirmed several tens of these candidates. in this work, we present our latest exciting results, focussing on the spectroscopic confirmation of the warm giant toi-199 b, which we first identified in tess photometry as a single transitter. we confirm and characterize the planet using tess photometry (sectors 1-13 and 27-36), ground-based photometry from astep in antarctica, and radial velocities from feros, harps, coralie, and chiron. orbiting a g-type star, toi-199 b has a 104.83-day period, a mass of 0.12mj, and a radius of 0.8rj. it is the first exo-saturn in this period range with a precisely determined mass and radius. the tess and astep transits also show strong transit timing variations, pointing to the existence of a second, non-transiting planet in the system. the analysis of the radial velocities and ttvs reveals toi-199 c to have a period of 279.92 days, and a minimum mass of 0.51mj. this period places it within the inner edge of the optimistic habitable zone. | the wine survey. a transiting 100-day exo-saturn with a companion in the habitable zone |
extrasolar planets (exoplanets) are the most intriguing objects in astronomy. currently, over 4,000 exoplanets have been discovered. among them, about 100 terrestrial ones are in habitable zones, where planetary surface conditions are theoretically suitable with the presence of liquid water. practicing advanced equipment, technology and method, more sufficient information will enable us to analyze the habitability of exoplanet more systematically. given the rapid development of space telescopes, capability of characterizing the extrasolar planetary atmospheres and surfaces will be achieved in near future, offering opportunities for direct observation. ocean has much lower albedo in comparison with land, thus a terrestrial planet largely covered by oceans can be identified via photometric variability as it spins. several models for simulating the variability have been discussed in literature, and we establish models of photometric variability for habitable terrestrial planets. in this project, oceans and growth of green plants have emerged. feasibility of identifying habitable planets and habitable moons will be examined with these more realistic models. | feasibility on characterizing earth-like planets by their optical variation |
water-rich exoplanets are a type of terrestrial planet that is water-rich and whose ocean depth can reach tens to hundreds of kilometers with no exposed continents. due to the lack of exposed continents, neither western boundary current nor coastal upwelling exists, and ocean overturning circulation becomes the most important way to return the nutrients deposited in the deep ocean back to the thermocline and to the surface ocean. here we investigate the depth of the thermocline in both wind-dominated and mixing-dominated systems on water-rich exoplanets using the global ocean model mitgcm. we find that the wind-driven circulation is dominated by overturning cells through ekman pumping and subduction and by zonal (west-east) circum-longitudinal currents, similar to the antarctic circumpolar current on earth. the wind-influenced thermocline depth shows little dependence on the ocean depth, and under a large range of parameters, the thermocline is restricted within the upper layers of the ocean. the mixing-influenced thermocline is limited within the upper 10 km of the ocean and cannot reach the bottom of the ocean even under extremely strong vertical mixing. the scaling theories for the thermocline depth on earth are applicable for the thermocline depth on water-rich exoplanets. however, due to the lack of exposed continents, the zonal and meridional flow speeds are not in the same magnitude as that in the oceans of earth, which results in scaling relationships for water-rich exoplanets being a little different from that used on earth. | thermocline depth on water-rich exoplanets |
direct imaging observations of exoplanets will help identify earth-like planets around sun-like stars. planned and future missions, such as the large space-based infrared/optical/ultraviolet (ir/o/uv) telescope prioritized in astro2020, are planned to have instrumentation capable of exoplanet direct imaging, such as a coronagraph and wavefront sensing and control system. determining whether a planet is in the habitable zone of its star may be difficult in multi-planet systems, which are now known to occur frequently. previous work (keithly et al. 2021) has shown that planets in multi-planet systems can be "confused" in direct images of a system taken over multiple epochs due to lack of prior knowledge about the planets' orbital parameters or planetary characteristics. being able to differentiate planets in multi-planet systems is necessary in order to determine orbital parameters, perform observation scheduling, characterize atmospheres, and determine habitability. in this work, we address the confusion problem using photometric observations, such as planetary orbital phase, in a "deconfusion" algorithm to help differentiate between multiple planets in an image. the deconfusion algorithm our team has developed is designed to accept unlabeled detections of planets, accompanied by astrometric information, and generate a list of orbit parameter matches constrained by an eccentricity threshold. the matches are then ranked based on their consistency with the presented data and the number of matched observations. however, this method of ranking alone may not be enough to solve the confusion and observation scheduling problem. we introduce the inclusion of orbital phase considerations in the deconfusion algorithm to help rank and further differentiate the matched orbit combinations. with a large number of simulated planetary systems, we are investigating the utility of orbital phase (color, intensity) information for each planet to reduce the rate of confusion in a multi-planet system. we present preliminary orbit matching rates for planets that include simulated photometric information. our results will be used to determine the ability of photometric information to mitigate confusion and improve observation scheduling techniques for future direct imaging missions. | the role of exoplanet photometry in orbit-fitting of directly imaged multi-planet systems |
considering subglacial liquid water, a significant extension of the classical habitable zone is obtained. elaborating on the model of wandel it is shown how an atmosphere and liquid water could survive on tidally locked planets closely orbiting an m-dwarf host, extending the habitable zone boundary inwards. in addition, subglacial liquid water could extend the habitable zone beyond the outer boundary of the conservative habitable zone as well. these two results enhance the circumstellar region with a potential for liquid water well beyond the conservative boundaries of the classical habitable zone. it is argued that the probable recent jwst detection of atmospheric water vapor on the rocky earth-sized exoplanet gj 486 b, along with earlier detections of water on other planets orbiting m-dwarf stars, gives an empirical answer to the much-argued question of whether such planets can support liquid water, organic chemistry, and eventually life. it is shown how water on terrestrial planets closely orbiting m-dwarf stars may sustain in a subglacial melting layer. finally, the model is applied to a few exoplanets demonstrating how water detection may constrain their atmospheric properties. | extended habitability of exoplanets due to subglacial water |
the astro2020 decadal survey recommended a "future large ir/o/uv telescope optimized for observing habitable exoplanets and general astrophysics" that would "search for biosignatures from a robust number of about ~25 habitable zone [exo]planets," now dubbed the habitable worlds observatory (hwo). the search for biosignatures requires high quality spectra of broad bandwidth and sufficient signal-to-noise. the combination of spectral resolution, bandwidth, and signal-to-noise-ratio impacts the number of exo-earths that can be spectrally characterized. previous work (morgan et al. 2022), evaluated the number of earth-size, habitable zone exoplanets that could be spectrally characterized for a range of spectral resolutions, signal-to-noise ratios, and bandwidths for a 6-m diameter exoplanet direct imaging mission. in this paper, we evaluate yield with two of those metrics for a range of parameters: aperture diameter, inner working angle, contrast, and exozodiacal dust brightness around a 6-m diameter telescope point design that is a blend of scaled habex and luvoir designs. the first metric is the water line search metric, which has spectral resolution = 70, snr = 5, bandwidth = 20%, wavelength = 800-1000 nm and which was used to establish the ~25 hz exoplanet goal of the astro2020. the second metric is a broadband metric that covers 500 – 1000 nm in four 20% bandwidth sub-bands. the sub-bands are tailored to minimize integration for each sub-band: 500 – 700 nm uses r=7 to look for rayleigh scattering, 700 – 850 nm uses r=140 for the oxygen line, and 800 – 1000 nm uses r=70 for the water line; all have snr = 8.5. | a sensitivity study in two yield metrics over an option space local to a 6m hwo telescope |
aims: a transiting planet candidate with a sub-neptune radius orbiting the nearby (d = 51.9 ± 0.07 pc) m1.5 v star toi-1470 with a period of ~2.5 d was announced by the nasa transiting exoplanet survey satellite (tess), which observed the field of toi-1470 in four different sectors. we aim to validate its planetary nature using precise radial velocities (rvs) taken with the carmenes spectrograph.methods: we obtained 44 rv measurements with carmenes spanning eight months between 3 june 2020 and 17 january 2021. for a better characterization of the parent star activity, we also collected contemporaneous optical photometric observations at the joan oró and sierra nevada observatories, and we retrieved archival photometry from the literature. we used ground-based photometric observations from muscat and also from muscat2 and muscat3 to confirm the planetary transit signals. we performed a combined photometric and spectroscopic analysis by including gaussian processes and keplerian orbits to simultaneously account for the stellar activity and planetary signals.results: we estimate that toi-1470 has a rotation period of 29 ± 3d based on photometric and spectroscopic data. the combined analysis confirms the discovery of the announced transiting planet, toi-1470 b, with an orbital period of 2.527093 ± 0.000003 d, a mass of 7.32-1.24+1.21m⊕, and a radius of 2.18-0.04+0.04r⊕. we also discover a second transiting planet that was not announced previously by tess, toi-1470 c, with an orbital period of 18.08816 ± 0.00006 d, a mass of 7.24-2.77+2.87m⊕, and a radius of 2.47-0.02+0.02r⊕ . the two planets are placed on the same side of the radius valley of m dwarfs and lie between toi-1470 and the inner border of its habitable zone. | two sub-neptunes around the m dwarf toi-1470 |
results are presented from a study of manifestations of the activity of the dwarf gl 414a of spectral class k7 with two planets, one of which (the planet gl 414a b) with an eccentricity e=0.45 was found to be within the habitable zone over a large part of its orbit. our analysis showed that the most reliable determination of the rotation period of gl 414a was obtained from an analysis of photometric observations of the star in the kelt (kilodegree extremely little telescope) survey which yield a rotation period of p=42 days. however, the existence of this period is not confirmed by periodograms constructed from other observations of gl 414a. the long-term activity cycle of the star is on the order of 3800 days (10.4 years). the obtained data on the activity of the star were used to estimate the loss of matter from the atmosphere of the planet gl 414a b using an approximation formula for a model of atmospheric loss with a limit on energy. based on 486 estimates of the parameter shk, the loss of matter by the atmosphere of gl 414a b over an interval of 5805 days (15.9 years) was calculated. the magnitude of these losses mainly lies within a range of log(mloss) from 7.15 to 7.50 with a median of 7.30. for an eccentricity of 0.45 the distance from the central star to gl 414a b ranges from 0.13 to 0.34 a.u., and for these distances the estimated losses of matter by the atmosphere are 16.21.1017 and 2.37.1017 g/s, respectively. | activity of the star gl 414a with two planets and its effect on the loss of mass of the atmosphere of the planet gl 414a b |
m dwarfs are the most abundant stars in the solar neighborhood and they are prime targets for searching for rocky planets in habitable zones. consequently, a detailed characterization of these stars is in demand. the spectral sub-type is one of the parameters that is used for the characterization and it is traditionally derived from the observed spectra. however, obtaining the spectra of m dwarfs is expensive in terms of observation time and resources due to their intrinsic faintness. we study the performance of four machine-learning (ml) models-k-nearest neighbor (knn), random forest (rf), probabilistic random forest (prf), and multilayer perceptron (mlp)-in identifying the spectral sub-types of m dwarfs at a grand scale by deploying broadband photometry in the optical and near-infrared. we trained the ml models by using the spectroscopically identified m dwarfs from the sloan digital sky survey (sdss) data release (dr) 7, together with their photometric colors that were derived from the sdss, two-micron all-sky survey, and wide-field infrared survey explorer. we found that the rf, prf, and mlp give a comparable prediction accuracy, 74%, while the knn provides slightly lower accuracy, 71%. we also found that these models can predict the spectral sub-type of m dwarfs with ~99% accuracy within ±1 sub-type. the five most useful features for the prediction are r - z, r - i, r - j, r - h , and g - z, and hence lacking data in all sdss bands substantially reduces the prediction accuracy. however, we can achieve an accuracy of over 70% when the r and i magnitudes are available. since the stars in this study are nearby (d ≲ 1300 pc for 95% of the stars), the dust extinction can reduce the prediction accuracy by only 3%. finally, we used our optimized rf models to predict the spectral sub-types of m dwarfs from the catalog of cool dwarf targets for the transiting exoplanet survey satellite, and we provide the optimized rf models for public use. | applied machine-learning models to identify spectral sub-types of m dwarfs from photometric surveys |
informed by the science cases and options for the luvoir and habex concepts, we present here a summary of an independent analysis by nasa exep to produce a list of priority target stars amenable to surveys for potentially habitable exoplanets via imaging with the ~6-m ir/o/uv space observatory recommended by astro2020. it is hoped that this list will stimulate investigations of the properties of these stars and their planetary systems to inform target prioritization and inform the modeling and interpretation of exoplanet spectra. to achieve the decadal goal to "provide a robust sample of ~25 atmospheric spectra of potentially habitable exoplanets," the observatory will have severe constraints on its survey capability given the limited number of nearby stars whose habitable zones (hzs) will be accessible to starlight suppression techs (e.g. coronagraph, starshade), and whose small planets will be bright enough to measure spectra on reasonable timescales. from a compiled input sample of ~800 nearby stars, we conducted a thorough literature search for their basic properties and calculated magnitudes and angular separations for hypothetical small hz planets. by consideration of the brightnesses, planet-star brightness ratios, and angular separations of hypothetical planets placed at various phase angles and orbital radii in the hz, we iteratively down-selected stars that would have the brightest exo-earths at the widest angular separations until ~100 cumulative hzs were surveyed. the stars have mean(rms) values of: v=5.2(1.0)mag, rc=4.8(0.9)mag, dist=13(5)pc, teff=5700(700)k, [fe/h]=-0.1(0.2)dex, mass=1.0(0.2)msun, log(l/lsun)=0.0(0.5) dex. all are brighter than v<7.5 and rc<6.4, with types between f1v and m2v, and maximum distances by spectral class of 4pc(m), 13pc(k), 21pc(g), and 24pc(f). given reasonable assumptions about achievable exoplanet brightnesses and planet-star-brightness ratios, to get to ~100 cumulative hzs surveyed, one requires a starlight suppression solution that enables detection and spectral characterization of exo-earths down to inner working angles (iwas) of ~60-70 mas. the peer-reviewed exep target star catalog will be posted at the nasa exoplanet archive and updated periodically. | nasa exep mission star list of plausible targets for a future irouv direct imaging space observatory |
we leverage gaia dr2 parallactic distances to deliver new or revised estimates of planetary parameters and x-ray irradiation for a distance-limited (≲100 pc) sample of 27 gaseous planets (from super-earths to hot jupiters) with publicly available chandra and/or xmm observations, for which we carry out a homogeneous data reduction. for 20 planets with x-ray-detected host stars we make use of the photoionization hydrodynamics code ates to derive updated atmospheric mass outflow rates. the newly derived masses/radii are not consistent with the exoplanet.eu values for five systems: hd 149026b and wasp-38, for mass, and au mic b, hat-p-20, and hat-p-2 for radii. notably, the lower mass implies a (saturn-like) density of 0.86 ± 0.09 g cm-3 for hd 149026b. this independent estimate is consistent with the lowest values reported in the literature. separately, we report on the x-ray detection of gj 9827, hd 219134, and lhs 1140 for the first time. the inferred stellar x-ray luminosity of lhs 1140 ( ${1.34}_{-0.21}^{+0.19}\times {10}^{26}$ erg s-1) implies that lhs 1140 b is the least irradiated transiting super-earth known to orbit within the habitable zone of a nearby m dwarf. | planetary parameters, xuv environments, and mass-loss rates for nearby gaseous planets with x-ray-detected host stars |
a planet's history dictates its current potential to host habitable conditions and life. the concept of the continuously habitable zone (chz) has been used to define the region around a star most likely to host planets with long-term habitability. however, definitions of the chz vary in the literature and often conflict with each other. calculating the fraction of habitable zone planets in the chz as a function of stellar properties, we find that the quality of a star as a host for planets with long-term habitability and biosignatures depends strongly on the formulation of the chz used. for instance, older m stars are either excellent or suboptimal hosts for chz planets, depending on whether one's definition of habitability prioritizes the total time spent in the habitable zone or the continuity of habitable conditions from the delivery of volatiles to its current age. in this study, we focus on belatedly habitable zone (bhz) planets, i.e., planets that enter the habitable zone after formation due to the evolution of their host star. we find that between ~29% and 74% of planets in the habitable zone belong to this class of bhz planets, depending on the timescale for the delivery of volatiles. whether these planets can retain their volatiles and support habitable conditions is unclear. since bhz planets comprise a large portion of the planets we expect to survey for biosignatures with future missions, the open question of their habitability is an important factor for mission design, survey strategies, and the interpretation of results. | the abundance of belatedly habitable planets and ambiguities in definitions of the continuously habitable zone |
here we discuss terrestrial planet formation by using earth and our knowledge from various isotope data such as 182hf-182w, u-pb, lithophile-siderophile elements, atmospheric 36ar/38ar, 20ne/22ne, 36ar/22ne isotope ratios, the expected solar 3he abundance in earth's deep mantle and earth's d/h sea water ratios as an example. by analyzing the available isotopic data one finds that, the bulk of earth's mass most likely accreted within 10 to 30 million years after the formation of the solar system. proto-earth most likely accreted a mass of 0.5 to 0.6 mearth during the disk lifetime of 3 to 4.5 million years and the rest after the disk evaporated (see also lammer et al. 2021; doi: 10.1007/s11214-020-00778-4). we also show that particular accretion scenarios of involved planetary building blocks, large planetesimals and planetary embryos that lose also volatiles and moderate volatile rock-forming elements such as the radioactive decaying isotope 40k determine if a terrestrial planet in a habitable zone of a sun-like star later evolves to an earth-like habitat or not. our findings indicate that one can expect a large diversity of exoplanets with the size and mass of earth inside habitable zones of their host stars but only a tiny number may have formed to the right conditions that they could potentially evolve to an earth-like habitat. finally, we also discuss how future ground- and space-based telescopes that can characterize atmospheres of terrestrial exoplanets can be used to validate this hypothesis. | terrestrial planet accretion constrained by isotopes: implications for earth-like habitats |
with the recent launch of jwst, we are entering an exciting new phase of exoplanet science that will focus on characterizing exoplanetary atmospheres, including those of potentially habitable, terrestrial worlds. therefore, a comprehensive understanding of possible biosignatures that may be detected with the next generation of ground and space telescopes is needed. while some biosignature gases, such as oxygen, phosphine, isoprene and ammonia, have recently been reviewed in depth, these gases likely will be extremely difficult to detect with jwst in high mean molecular weight atmospheres. in contrast, methane at earth-like biogenic fluxes is one of the only biosignatures that may be readily detectable with jwst. in fact, an early earth-like, methane-rich atmosphere would be easier to detect with jwst than modern earth's oxygen-rich atmosphere. although there is a patchwork of prior studies on methane biosignatures, an up-to-date, dedicated assessment of the planetary conditions needed for methane to be a good exoplanet biosignature has been lacking. here we present our work on understanding the necessary planetary context for methane biosignatures and the potential false positive scenarios that arise from its abiotic sources. methane has been invoked as a potential biosignature due to its short photochemical lifetime (≤1 myr) on habitable-zone, rocky planets orbiting solar-type stars, which requires substantial replenishment fluxes to sustain large atmospheric abundances. on earth, life is the only source that can generate such large ch4 replenishment fluxes. although methane can be produced by various abiotic mechanisms including magmatic outgassing, water-rock and metamorphic reactions, and impact events, we find that known abiotic processes cannot easily produce atmospheres with abundant ch4 and co2 with comparatively little co due to the strong redox disequilibrium between ch4 and co2. we also explore whether temperate, terrestrial planets with large volatile inventories like titan could have long lifetimes of atmospheric ch4 and determine that the photochemical lifetime of such ch4 is still short. we conclude that methane is more likely to be biogenic for terrestrial planets with 1) a high mean molecular weight and anoxic atmosphere, 2) an atmospheric ch4 abundance that implies surface fluxes exceeding what could be generated by known abiotic processes, and 3) atmospheric co2 with comparatively little co. | when is atmospheric methane a good exoplanet biosignature? |
the discovery of earth-like exoplanets has profound implications for our understanding of the origins and diversity of life in our universe. as such, developing new and improved doppler radial velocity (rv) spectrometers capable of discovering and characterizing these planets is a high priority in the astronomical community. however, detection of true earth-analogs remains beyond the technical reach of current doppler rv instruments. this thesis discusses a number of technological developments designed specifically to overcome classical instrumental limitations of high precision doppler rv measurements. these technologies are essential components of next generation instruments that aim to achieve the rv precision necessary to detect low-mass planets. this instrumentation research is driven by the development of the habitable-zone planet finder (hpf), a near-infrared (nir) doppler spectrograph currently under development at penn state that will detect terrestrial-mass planets orbiting nearby m-dwarfs. furthermore, many technologies discussed will also be applied to the nasa-nsf extreme precision doppler spectrometer concept neid, a doppler rv instrument for the 3.5 meter wiyn telescope, slated for delivery in 2019. neid is an ultra-stable, high resolution optical spectrometer also under development at penn state. this thesis describes new specialized optical fiber delivery systems, designed to significantly improve instrument illumination stability, modal noise suppression systems, which suppress mode interference in optical fibers and allow spectrometers to fully realize the exquisite precision of modern wavelength calibration sources, and new photonic calibration sources, which show significant promise as potential doppler wavelength references. these technologies represent important steps in enabling next generation instruments to reach precisions sufficient to detect terrestrial-mass planets orbiting in the habitable-zones of nearby stars. improving measurement capabilities in both the optical and nir is not only essential for enabling precision rv studies on a wide variety of stars, but can also aid in disentangling stellar activity signals from true reflex motion. beyond independent planet discoveries, these instruments will be indispensable tools for measuring masses and densities of planets identified by future space observatories, and play key roles in directing future atmospheric characterization studies with the james webb space telescope. | photonic systems for high precision radial velocity measurements |
the transiting exoplanet survey satellite (tess) is nasa's ongoing mission to discover planets outside the solar system, and to explore the bright and time-variable sky. tess uses 4 optical telescopes to repeatedly acquire images of a 24° by 96° field. the field is switched every 27 days to progressively cover the entire sky. science operations began in july 2018. the observatory is healthy; the scientific output has grown rapidly, with a tess publication rate of ~8 papers per week in 2021. tess is discovering transiting planets orbiting stars in the solar neighborhood that are bright enough to enable follow-up spectroscopic measurements of the planet's mass, orbital characteristics, and atmospheric properties. tess's high photometric precision has led to the detection of >5,000 planet candidates, the largest number of detections of any ongoing survey. the candidates are being confirmed through a world-wide effort with ground-based telescopes, open to any interested astronomer. the main goal of the tess prime mission — to detect 50 planets smaller than neptune and measure their masses — has been achieved. during the ongoing 1st extended mission (em1; 2021-2022), the catalog of planet candidates has expanded to include a wider range of planet sizes and orbital periods. this includes planets in the habitable zones of low-mass stars, which offer the best prospects for atmospheric characterization with the webb telescope and other facilities. thus, tess spearheads progress toward the ultimate goal of finding life elsewhere in the galaxy, a major priority expressed in the 2020 astronomy and astrophysics decadal survey. the 2nd extended mission (em2; 2023-2025) will bring the cumulative sky coverage to more than 95%. in addition, more than 80% of the sky will have been observed at least twice, giving access to longer-period planets. through changes to the downlink schedule, the time sampling of tess images will be improved from 600 to 200 sec, allowing stars to be searched for transit signals without appreciable time smearing and without needing to preselect stars of interest. em2 will increase the number of planet candidates to >10,000, and will also feature an accelerated data delivery schedule, with calibrated image data available at the public data archive within 5 days of downlink. tess is an engine that is rapidly driving progress in exoplanetary science, a finderscope that identifies targets for intensive observations with webb and other major observatories, and a source of precise time-domain optical photometry for all areas of astrophysics: a fundamental and lasting legacy for the astronomical community. | the transiting exoplanet survey satellite (tess) |
the climates of terrestrial planets with a small amount of water on their surface, called land planets, are significantly different from the climates of planets having a large amount of surface water. land planets have a higher runaway greenhouse threshold than aqua planets, which extends the inner edge of the habitable zone inward. land planets also have the advantage of avoiding global freezing due to drier tropics, leading to a lower planetary albedo. in this study, we systematically investigate the complete freezing limit for various surface water distribution using a three-dimensional dynamic atmospheric model. as in a previous study, we found that a land planet climate has dry tropics that result in less snow and fewer clouds. the complete freezing limit decreases from that for aqua planets (92% s0, where s0 is earth's present insolation) to that for land planets (77% s0) with an increasing dry area. values for the complete freezing limit for zonally uniform surface water distributions are consistently lower than those for meridionally uniform surface water distribution. this is because the surface water distribution in the tropics in the meridionally uniform cases causes ice-albedo feedback until a planet lapses into the complete freezing state. for a surface water distribution using the topographies of the terrestrial planets, the complete freezing limit has values near those for the meridionally uniform cases. our results indicate that the water distribution is important for the onset of a global ice-covered state for earth-like exoplanets. | the onset of a globally ice-covered state for a land planet |
one of the major developments in the past year has been the first detection of h2o in the atmosphere of the mini-neptune k2-18b orbiting in the habitable-zone of its host star, with an equilibrium temperature of ~300 k. the observations revealed an h2-rich atmosphere with strong absorption from h2o, but also a surprising paucity of methane (ch4) and ammonia (nh3). given the low temperatures in the atmosphere, ch4 and nh3 are expected to be the prominent carriers of carbon and nitrogen in a h2-rich atmosphere. the non-detections of ch4 and nh3, therefore, suggest strong thermochemical disequilibrium in the atmosphere of k2-18b, similar to the "missing methane problem" in other low-mass planets which is one of the longest-standing conundrums in exoplanetary atmospheres. given its low temperature and high observability, k2-18b serves as the perfect test case for investigating this problem and for understanding physical and chemical processes in exoplanetary atmospheres in the temperate regime. we propose to conduct unprecedented observations of k2-18b to resolve this long-standing puzzle. using jwst broadband transmission spectroscopy with niriss, nirspec and miri, our observations aim to make the first detections of ch4 and nh3 in k2-18b and place unprecedented constraints on chemical disequilibrium in its atmosphere. | chemical disequilibrium in a temperate sub-neptune |
we report precise radial velocity observations of hd 212657 (= k2-167), a star shown by k2 to host a transiting planet in a 9.97857 day orbit. using observations from tess, we refined planet parameters, especially the orbital period. we collected 76 precise radial velocity observations with the harps-n spectrograph between august 2015 and october 2016. although this planet was first found using the transit method in 2015 and validated in 2018, stellar jitter originally limited our ability to measure its mass. in this work, we demonstrate that a new machine learning inspired method can successfully mitigate stellar jitter and reveal the mass of k2-167 b. in the future, these or similar techniques could be widely applied to solar-type (fgk) stars, help measure masses of planets from tess to fulfill the level 1 science requirement, and eventually help detect habitable-zone earth-mass exoplanets. | a machine learning inspired method reveals the mass of k2-167 b |
statistical distributions of exoplanets obtained by both ground-based and satellite telescopes are heavily distorted by observational selection. it is easier to detect massive planets orbiting close to the star, rather than planets of small masses and planets with large orbital periods. low-mass planets with orbital periods of about a year or more, falling in the habitable zone of sun-like stars, cannot be detected by modern means. to account for this factor, we proposed and investigated the method of correcting the observational selection. it has been shown that the corrected mass distributions of exoplanets are well described by a piecewise power law. the result is in agreement with the conclusions of cosmogony and demonstrates a number of new features. | the mass and orbital-period distributions of exoplanets accounting for the observational selection of the method for measuring radial velocities. a dominant (averaged) structure of planetary systems |
the trappist-1 system is home to at least seven terrestrial planets and is a target of interest for future james webb space telescope (jwst) observations. additionally, these planets will be of interest to future missions making observations in the ultraviolet (uv). although several of these planets are located in the traditional habitable zone, where liquid water could exist on the surface, trappist-1h is interesting to explore as a potentially habitable ocean world analog. in this study, we evaluate the observability of a titan-like atmosphere on trappist-1h. the ability of the jwst or a future uv mission to detect specific species in the atmosphere at trappist-1h will depend on how far each species extends from the surface. in order to understand the conditions required for detection, we evaluate the input parameters used in one-dimensional models to simulate the structure of titan-like atmospheres. these parameters include surface temperature and pressure, temperature profile as a function of distance from the surface, composition of the minor species relative to n2, and the eddy diffusion coefficient. we find that jwst simulated spectra for cloud- and haze-free atmospheres are most sensitive to surface temperature, temperature gradients with altitude, and surface pressure. the importance of temperature gradients in jwst observations shows that a simple isothermal scale height is not ideal for determining temperature or atmospheric mean molecular mass in transit spectra from exoplanet atmospheres. we demonstrate that uv transmission spectra are sensitive to the upper atmosphere, where the exobase can be used to approximate the vertical extent of the atmosphere. | trappist-1h as an exo-titan. i. the role of assumptions about atmospheric parameters in understanding an exoplanet atmosphere |
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