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in order to assess the habitability of planets around other stars we need to consider all possible influences on that system. we investigated whether any of the known habitable-zone exoplanet systems could be destroyed by a nearby supernova. we used an existing exoplanets database to define a collection of systems with habitable-zone planets. we only considered planet masses less than 1 jupiter mass. our final sample for this investigation includes 24 stars possessing at least one habitable-zone planet. we search the gaia edr3 catalog within a sphere having a radius of 100 light-years around each host star to find any other stars that might supernova. finally, we use panstarrs to identify which, if any, of those stars that are spectral type b3 or hotter as potential supernova progenitors. | determining the habitability of earth-like exoplanets through an analysis of their eventual destruction by supernova |
star systems consisting of two or more stars are very abundant in our stellar neighbourhood which makes them interesting candidates for the search of life. for single star systems there exist different climatic models (e.g. kasting et al. 1993 and kopparapu et al. 2013) to determine the habitable zone, that defines the region around a star where liquid water could exist on the surface of a terrestrial planet. in binary and multiple star systems the radiation from the stellar companion(s) can influence the size and location of the habitable zone of the system. especially for binaries with small stellar separation and/or in binaries where the planets orbit the less luminous star, the amount of the stellar flux received by the planet from the secondary star can be significant. for s-type binaries, where the planet orbits one of the two stars, eggl et al. 2012 proposed a model that includes the dynamical influence of the secondary star to the climatic model. in this poster calculations for the habitable zone around s-type binaries - using data from the catalogue of exoplanets in binary star systems - will be presented. | habitability of exoplanets in binary and multiple star systems |
this code reproduces the figure and calculations on the research note of the aas entitled "on the transit probability of the habitable-zone exoplanet gj 357 d" | transit probability calculation for gj 357 d |
space-based missions such as kepler, and now tess, provide large datasets that must be analyzed efficiently and systematically. shallue & vanderburg (2018) recently used state-of-the-art deep learning models to successfully classify kepler transit signals as either exoplanets or false positives. we expand upon that work by including additional “scientific domain knowledge" into the network architecture and input representations to significantly increase overall model performance to 97.5% accuracy and 98.0% average precision. notably, we achieve 15-20% gains in recall for the lowest signal-to-noise transits that can correspond to rocky planets in the habitable zone. this work illustrates the importance of including expert domain knowledge in even state-of-the-art deep learning models when applying them to scientific research problems that seek to identify weak signals in noisy data. | automatic classification of transiting planet candidates using deep learning |
we are investigating the science case for a 1.0-1.4 meter space telescope to survey the closest, brightest fgkm main sequence stars to search for habitable zone (hz) earth analogs using the precise radial velocity (prv) technique at a precision of 1-10 cm/s. our baseline instrument concept uses two diffraction-limited spectrographs operating in the 0.4-1.0 microns and 1.0-2.4 microns spectral regions each with a spectral resolution of r=150,000~200,000, with the possibility of a third uv arm. because the instrument utilizes a diffraction-limited input beam, the spectrograph would be extremely compact, less than 50 cm on a side, and illumination can be stabilized with the coupling of starlight into single mode fibers. with two octaves of wavelength coverage and a cadence unimpeded by any diurnal, seasonal, and atmospheric effects, earthfinder will offer a unique platform for recovering stellar activity signals from starspots, plages, granulation, etc. to detect exoplanets at velocity semi-amplitudes currently not obtainable from the ground. variable telluric absorption and emission lines may potentially preclude achieving prv measurements at or below 10 cm/s in the visible and <50 cm/s in the near-infrared from the ground. placed in an earth-trailing (e.g. spitzer, kepler) or lagrange orbit, the space-based cadence of observations of a star can be year-round at the ecliptic poles, with two ~100-day "seasons" every 6 months in the ecliptic plane. this will provide a distinct advantage compared to an annual ~3-6 month observing season from the ground for mitigating stellar activity and detecting the orbital periods of hz earth-mass analogs (e.g. ~6-months to ~2 years). finally, we are compiling a list of ancillary science cases for the observatory, ranging from asteroseismology to the direct measurement of the expansion of the universe. | earthfinder: a precise radial velocity survey probe mission of our nearest stellar neighbors for earth-mass habitable zone analogs using high-resolution uv-vis-nir echelle spectroscopy on a space platform |
evaporation of hydrogen and helium is now directly observable for exoplanets of jupiter and neptune size, by using high-resolution spectral observations in the ultraviolet and in the infrared. for even smaller planets, the ongoing loss of a primordial hydrogen-helium atmosphere has not been directly observed yet, but is thought to be relevant for the formation of a habitable atmosphere for life as we know it. the observability of helium escape depends critically on an exoplanet's irradiation in the high-energy regime. m dwarfs, typically a favourite target for habitable zone exoplanet observations, are at a disadvantage here due to their coronal elemental abundance patterns. however, k dwarfs present a suitable starting point for detecting helium escape from planets in their habitable zones, due to their favorable coronal abundances and their higher magnetic activity level compared to g dwarfs. i will discuss relevant examples and outline the impact that modern high-energy surveys can have on the optimal target selection for observing exoplanetary atmospheric escape. | habitability and loss of hydrogen-helium atmospheres of small planets - the k dwarf advantage |
high-energy particles from m-dwarf superflares--flares with energy (\geq 10^{33}) erg--can dramatically impact habitable-zone planets around these cool stars, with possible effects including the excitation of intense aurorae as particles interact with planetary atmospheres. prior work has demonstrated that earthlike atmospheres can produce excess emission in m-dwarf spectra, with the star/planet contrast ratio increasing by orders of magnitude in the green 5577-å auroral line to levels potentially detectable by future surveys. the evryscopes are gigapixel-scale telescope arrays at mount laguna observatory and cerro-tololo inter-american observatory; coupled with the evryscope fast transient engine (efte), which scans evryscope images in real time for transient phenomena, the systems have the unprecedented ability to identify superflares across the entire sky as they begin, enabling rapid spectroscopic follow-up. with the evryscopes' all-sky coverage, far more--and far brighter--flares are observable than in surveys that focus on individual targets. using the goodman spectrograph on the 4.1-m soar telescope, we follow the spectroscopic evolution of m-dwarf superflares as they happen. preliminary results include the strongest-yet upper limits to be placed on auroral emission in the atmospheres of earthlike planets orbiting m-dwarf stars. | constraints on post-superflare exo-auroral emission with soar and the evryscope fast transient engine |
coronal mass ejections (cmes), enormous releases of energy from the sun, can have significant space-weather implications for earth. do similar storms from smaller stars m dwarfs like v374 peg, or the nearby proxima centauri mean bad news for the planets that these stars host?volatile starsdifference in habitable-zone sizes for different stellar types. [nasa]when plasma is released from the sun in the form of a cme traveling toward earth, these storms can be powerful enough to disrupt communications and navigational equipment, damage satellites, and cause blackouts even with our planetary magnetic field to protect us! how might planets in the habitable zone of m-dwarf stars fare against similar storms?the first danger for an m dwarfs planets is that the habitable zone lies much closer to the star: it can range from 0.03 to 0.4 au (i.e., within mercurys orbit). being so close to the star definitely makes a planet in an m dwarfs habitable zone vulnerable to storms.colors indicate the probability of cme impact, for different different stellar latitudes where the cme originated vs. orbital inclination of the planet, (a) without any deflection, and (b) taking into account the cme deflection by the stars magnetic field. hanging out in an orbit aligned with the current sheet turns out to be a bad idea. [adapted from kay et al. 2016]what about the storms themselves? you might think that because m dwarfs are cooler stars, they would be quieter, releasing fewer cmes with less energy. surprisingly, the opposite is true: m dwarfs are significantly more active than solar-type stars, and the cmes are typically ten times more massive than those released from the sun. impacts from these powerful outbursts could easily strip any existing planet atmosphere, making a planet much less likely to be habitable. to make matters worse, m dwarfs can remain magnetically active for billions of years: even a star like proxima centauri, which is nearly 5 billion years old, isstill relatively active.dodging deflected stormsinterestingly, an important factor in the survival of an m dwarfs habitable-zone planet is the plane in which the planets orbit lies. a team of scientists led by christina kay (nasa goddards solar physics laboratory and boston university) recently modeled cmes from v374 peg, a mid-type m dwarf of roughly a third of the suns mass and radius, to determine how the cmes propagate and the probability that theyll impact a hypothetical planet in the stars habitable zone.the team shows that traveling cmes tend to be deflected by the stars magnetic field. instead of propagating purely radially outward, the cmes are pushed toward the astrospheric current sheet the minimum point of the background magnetic field which moves around, but is generally located toward the stellar equatorial plane.kay and collaborators find that planet orbits roughly aligned with the current sheet therefore have a higher probability of getting hit by a cme: around 10%. in contrast, planets with higher-inclination orbits have cme impact probabilities around 1%. these probabilities translate to an impact rate of about 0.55 times per day for a habitable-zone planet around a mid-type m dwarf which is 220 times the average at earth during solar maximum!minimum planetary magnetic field strength required to sustain a magnetosphere twice the size of the planetary radius for different cme masses and speeds, for a 1 kg (left) and 20 kg (right) initial cme magnetic field strength. a typical cme requires a field strength of 10100 g. [adapted from kay et al. 2016]is there hope for planet habitability?with this many cme impacts even outside of the current-sheet plane, how can a planet hope to survive? the key lies in having a strong magnetic field to protect the planet. such a field would deflect the charged particles from the cme, preventing the cme from stripping the planets atmosphere.kay and collaborators calculate that a habitable-zone mid-type m-dwarf exoplanet would need a planetary magnetic field between tens and hundreds of gauss 1 to 2 orders of magnitude more than that of earth to protect itself from these cmes: difficult to muster, but not impossible!these results provide some interesting food for thought as we continue to discover new exoplanets orbiting m-dwarf stars.citationc. kay et al 2016 apj 826 195. doi:10.3847/0004-637x/826/2/195 | are stellar storms bad news for m-dwarf planets? |
since the discovery of the first extrasolar planet 51 pegasi b, almost five thousand exoplanets have been detected and confirmed by several astronomical facilities both space and ground based. the higher the number of confirmed exoplanets the more justified is the human issue about the possibility of other life forms in the universe. life as we know needs at least the following requirements: liquid water, an energy source, availability of nutrients and complex carbon chemistry. investigation of life in the universe is necessarily based on what we know from our planet. on earth, oxygenic photosynthesis (op) is by large the most important biochemical process to produce biomass. due to the general availability of its input chemical ingredients and stellar energy, it is possible to conjecture that op might be a very common biochemical process on other habitable planets. we investigated the efficiency of op as a function of the host star temperature and the planet-star separation (covone et al.,2021,magliano et al., in prep.). in particular, for a dataset of known earth-analogues in their habitable zone we computed the photon flux and the exergetic efficiency of the op process and compared with the earth values. the calculations have been performed in the so called photosynthetically active radiation (par) whose wavelength range is still debated. due to the ambiguity on the universality of the par, we updated those calculations (magliano et al. in prep.) with a more detailed study based on the latest predictions of the absorption peaks spectra of photosynthetic organisms (arp et al.,2020). this is based on a noisy-quieting antenna model to retrieve the absorption peaks for green plants, purple bacteria and green sulfur bacteria under the solar radiation exposure. we applied this tool using different stellar spectra and discuss some preliminary results regarding the dependence of the absorption peaks of extra-terrestrial organisms with respect to the host star temperature. | the efficiency of the oxygenic photosynthesis on earth-like planets in the habitable zone |
the habex and luvoir concepts aim to directly image and spectrally characterize potentially habitable exoplanets. using exosims, realistic mission observing constraints, and dynamically responsive scheduling, we simulate the exoplanet detection and characterizations over monte carlo realizations of synthetic planets around nearby stars. we use identical astrophysical inputs and the observing scenarios of each concept to evaluate a common comparison of the detection and spectral characterization yields of habex and luvoir. habex is evaluated for the 4m hybrid starshade and coronagraph architecture, the 4m coronagraph only architecture, and the 3.2 m starshade only architecture. luvoir is evaluated for the 15 m on-axis and 9 m off-axis architectures. the scenarios are scheduled to respond dynamically to the number of detections/no-detections of a target and success of characterization as well as the optimal slews for the starshade. yield analysis shows that both concepts can directly image and spectrally characterize earth-like planets in the habitable zone and that each concept has complementary strengths. | updated standard evaluation of exoplanet yield for the luvoir and habex concept studies |
we examine how space weather impacts a planet's atmospheric chemistry and climate. the young sun would have been more magnetically active and should have experienced more frequent coronal mass ejections (cmes), bombarding the planet's upper atmosphere with solar energetic particles (seps). these particles helped drive atmospheric chemistry, potentially resulting in heightened concentrations of the greenhouse gas, nitrous oxide, n2o (airapetian et al.,2016). we are using the particle-transport code, hzetrn, and our own photochemical and climate models to reinvestigate these claims and also to extend this mechanism to a broader planetary context. our photochemical model includes vertical eddy transport of species, a robust treatment of hydrocarbon haze production, and updated photolysis and chemical reactions -some of which has been lacking in previous calculations. we first attempt to reconfirm the predictions made for the early earth in the literature using our own independent models. we will use the models constructed for the early earth, as well as observational constraints of sep fluxes at mars associated with the solar wind and cme's, to evaluate the impact space weather could have had on early martian climate. we will then apply our models to the question of biosignatures on exoplanets. n2o is a possible biosignature molecule, as its sources are almost entirely biological. we can use our photochemical model as well as the sophisticated radiative transfer code, smart, to simulate synthetic spectra for rocky exoplanets. our work could ascertain whether n2o is a good biomarker molecule or a 'false positive' for life detection. additionally, the stellar environments that would promote n2o production would also drive the buildup of organic haze. while organic haze is known to have an anti-greenhouse effect, pushing the inner edge of the habitable zone closer to the star, n2o would also be able to buildup due to the uv shielding provided by the haze- pushing the inner edge back out. the effect on planetary habitability for different planetary and stellar conditions will be explored. | effect of space weather on atmospheric chemistry and climate |
the earth's crust is strongly depleted in the biological elements cnps as well as water relative to primitive meteorites. these elements did not condense within the earth's accretion zone; they were volatilized to space during planetary collisions, and/or they sunk into the earth's iron core. the earth's inventories arrived within minor outer solar system objects. we can extrapolate that life does well with meagre supplies of biological elements and that the distal regions of stellar systems do provide these elements. life strongly modulates the subsequent rock, ocean, and atmosphere cycles of these elements. these contingencies limit what details can be exported to earthlike exoplanets. with regard to c-rich exoplanets, a graphite rind develops during accretion. a rind of frozen metallic silicon develops on si-rich planets. even in these cases, the outer stellar system supplies the locally rare elements chonps. life evolves to prosper in the conditions it actually faces. for example, the rinds are strongly reducing. life will probably evolve ways to gather, create, store, and utilize oxidants that are far from equilibrium with the general environment. | planetary interior-atmosphere interaction and habitability |
interaction with the stellar wind and accompanying radiation can result in significant atmospheric erosion, potentially affecting a planet's ability to host life. previous research indicates the atmospheres of close-in, low-mass planets are highly vulnerable to the effects of xuv driven photoevaporation. however, the effects of the stellar wind on low-mass exoplanet atmospheres have only just begun to be addressed. we present 3d magnetohydrodynamical (mhd) simulations of the effect of the stellar wind on the escaping atmosphere of a magnetized planet in the habitable zone of a low-mass m dwarf. we use the trappist-1 system as the basis of our simulations and model the planet to have an h-rich evaporating outflow, with a pre-defined mass loss rate. our results show the atmospheric outflow is dragged and accelerated upon interaction with the stellar wind, resulting in a diverse range of planetary magnetospheres which are strongly dependent on the local stellar wind conditions through the orbit and can vary over timescales as short as an hour. we explore the implications of this wind-outflow interaction on potential observations of escaping atmospheres and show that stellar wind interactions provide an explanation for observed variations in transit absorption features. | mhd effects of the stellar wind on observations of escaping exoplanet atmospheres |
precision radial velocity (rv) surveys use high resolution spectrographs in the optical and near-infrared to search for exoplanets. in this presentation we describe our pipeline and preliminary results to search for unresolved laser technosignatures in m dwarf spectra observed by the habitable-zone planet finder (hpf). hpf is a nir fiber-fed spectrograph located at the 10 m hobby eberly telescope in texas, usa, that has been observing m dwarfs as part of its guaranteed time survey for the past 3 years. developing a general pipeline to search for lasers in stellar spectra from fiber-fed spectrographs, opens up the possibility to search for (and place limits on) laser technosignatures, utilizing the decades of data from rv surveys. | searching for lasers in m dwarf spectra using the habitable-zone planet finder |
the surface features of distant potentially habitable worlds are unknown and likely to remain so for the foreseeable future. as a result, 3-d general circulation model (gcm) simulations of the climates of these worlds commonly utilize an aquaplanet configuration (no emergent land). we highlight here the differences in simulated climates that are produced when using realistic, reconstructed, or idealized continental distributions. paleo-earth scenarios as analogues of habitable exoplanets with emergent land exist back to 2 gyr. there is high confidence in continental reconstructions back to 300 myr, with moderate confidence reconstructions dating to at least 1 gyr. a range of habitable states exists throughout the last two billion years of earth history, including periods that are representative of both inner and outer edge environments, i.e., snowball earth and the cretaceous greenhouse. using reconstructed land/ocean distributions with the gcm permits us to test hypotheses based on conceptual models (does a supercontinent at tropical latitudes encourage global cooling via albedo feedbacks?) as well as explore far-field climate teleconnections that may explain enhanced habitability (does the closing of an equatorial seaway drive increased heating in polar regions?). paleo-venus simulations, using current topography and a slow rotation rate, have shown that large land fraction in the tropics combined with modest amounts of water actually limits the amount of planetary warming to habitable levels, moreso than aquaplanets, given the equivalent solar flux - thus showing the inner edge of the hz to be more transitional than previously described. for distant exoplanets or paleo-earth prior to 2 gyr, idealized continents or modern earth topography help illustrate the range of possible habitable states for a given case. with idealized continents, varying the land fraction and location produces as much as a 20˚c difference in global mat for otherwise identical simulations (same solar/ghg forcings). synchronously rotating exoplanets modeled with modern earth topography show how land barriers to zonal water/heat transports result in a global mat considerably colder than the equivalent aquaplanet scenario, and ice and snow cover can increase by roughly a factor of two when land is beneath the substellar point. | the importance of topography in modeling the climates of potentially habitable worlds |
we do not understand the largest planets around the smallest and most numerous stars in the galaxy. m dwarfs are the most common type of stars in the galaxy. empirical studies show that they also play host to more inner planets than fgk stars, despite this, of the currently $\sim 5000$ confirmed exoplanets, only about 250 orbit m dwarfs, of which only $\sim 65$ have precise mass and radii measurements! the population of planets around m dwarfs is poorly understood. in this thesis i will discuss our efforts to detect and obtain precise measurements for planets around m dwarfs, and then to place this sample of m dwarfs in context of the larger sample of planets around fgk stars. the first part of my dissertation focusses on the instrumentation efforts for the habitable zone planet finder (hpf), and neid. hpf is a stabilized near-infrared (nir) fiber-fed radial velocity (rv) spectrograph at the 10 m hobby eberly telescope (het) at mcdonald observatory, texas, usa, while neid is a new high-precision spectrograph in the red-optical installed at the 3.5 m wiyn telescope at kitt peak, arizona, usa. i was in charge of developing, integrating and testing the fiber-feed for hpf, as well as the optical simulations to verify the alignment of the instrument. for neid, not only did i lead a similar effort for the fiber-feed and simulations, but was also responsible for the chromatic exposure meter which is essential to measure exposure midpoints for barycentric corrections. in conjunction, i developed the algorithm for performing these corrections, which are now used in hpf, neid and numerous other rv spectrographs. hpf with its large aperture and near-infrared bandpass, and neid with its red-optical coverage have already started to enable the rv follow up of planets around mid-to-late and early m dwarfs respectively. i then discuss some results from the hpf rv survey, where first i test the scrambling performance of hpf on the fixed altitude het using on-sky data on an m dwarf. then i present the results of a serendipitous observation of a flare around the ultracool dwarf vb 10. the hpf spectra taken during the flare show a red excess in the he 10830 \aa~triplet which is similar to observations of coronal rain for the sun, while also placing a limit on the atmospheric mass loss from flares for planets orbiting such stars. alongside the instrumentation and observational efforts, i also built upon a nonparametric framework to model exoplanet masses and radii (m-r), which was then applied to a sample of planets around m dwarfs. by comparing the results for m dwarf planets with those from fgk stars we notice some systemic differences in their distributions. however, further inferences were deterred by the small sample of transiting m dwarf planets with mass measurements. i then discuss the efforts to use hpf and neid to follow up on m dwarf planet candidates discovered by tess. not only do these planets help fill in the m-r plane for m dwarfs, but also highlight interesting correlations with stellar properties. finally, i conclude by giving an overview of how my work on instrumentation, algorithms and novel statistical frameworks has helped develop our understanding of the m dwarf planet population. the ongoing transiting gas giant follow-up will be continued in the future, which will help us shed further light on how these giant planets form around the smallest stars. | developing new tools and techniques to probe the m dwarf planet population |
before applying our magnetic moment model, we compile a data base of rocky exoplanets using the nasa composite exoplanet data base (akeson et al. 2013pasp..125..989a), in conjunction with the higher precision radii of kepler planets given in fulton & petigura (2018aj....156..264f, cat. j/aj/156/264) (table a1). unknown masses or radii and their associated uncertainties are estimated using chen & kipping (2017apj...834...17c, cat. j/apj/834/17) m-r relationship for terrestrial planets: rp~mp0.279+/-0.009. following the chen & kipping (2017apj...834...17c, cat. j/apj/834/17) definition of the boundary between terrestrial and jovian planets, we restrict our sample to exoplanets with radii rp=<1.23r{earth}, which corresponds to ~2m{earth}. these constraints restrict our sample to 496 rocky exoplanets (490 tidally locked), nine of which are located in the circumstellar habitable zone (chz) - where the chz is the insolation between recent venus and ancient mars as defined by the kopparapu et al. (2013apj...765..131k) optimistic habitable zone. eight of the nine rocky exoplanets from our chz subset are tidally locked. for each exoplanet we perform 10000 monte carlo simulations. these simulations allow us to determine the median and 68 per cent confidence intervals on mmax (maximum magnetic dipole moment) values. (1 data file). | vizier online data catalog: magnetic dipole moments on rocky exoplanets (mcintyre+, 2019) |
extremely precise radial velocity (eprv) measurements are critical for characterizing nearby terrestrial worlds. eprv measurement precisions of σrv =1-10 cm/s are required to study earth-analogs requiring sub-mk thermo-mechanical stability requirements of doppler spectrographs. with such constraints, to maximize the scientific capabilities of any new eprv instrument, a careful thermal and environmental control strategy must be developed as part of the instrument design process. ilocater is a new, high-resolution (r=190,500 median), near infrared eprv instrument under construction for the dual 8.4m diameter large binocular telescope (lbt). its diffraction-limited design enables a compact spectrograph design fabricated using intrinsically stable materials that reduce sensitivities to thermal changes. even with the use of these stable materials in fabrication however, the spectrograph must still be thermally stabilized to achieve its exoplanet science goals. we present the final design and performance of the ilocater environmental control system (ecs) that comprises the instrument cryostat and thermal control system that houses the ilocater spectrograph. the ecs includes an actively temperature-controlled radiation shield mounted inside a multi-layer-insulation (mli) lined vacuum chamber that surrounds the echelle spectrograph. building on the existing heritage of the habitable-zone planet finder (hpf) and neid instruments, the radiation shield provides sub-mk thermal stability at an operating temperature of 80-100k. the instrument operating temperature has been selected to minimize detector background effects while optimizing the instantaneous coefficient of thermal expansion (cte) of the materials used for spectrograph fabrication. this reduces the effects of thermomechanical changes on eprv measurement precision. | the ilocater environmental control system: delivering cryogenic thermal stability for eprv diffraction-limited spectrographs |
understanding stellar rotation and magnetic activity is critical to both the detection and characterization of exoplanets. this is particularly pertinent for planets around m dwarf stars, which remain magnetically active for gyrs and for which the habitable zone is at only a few tenths of an au. while these low-mass stars are the most common type of star in the galaxy, a lack of observational constraints at ages beyond 1 gyr has hampered studies of rotational evolution and magnetic activity. to address this, we have made new measurements of rotation and magnetic activity in nearby, field-age m dwarfs. our rotation period measurements are derived from photometry from the mearth planet-search data, and include detections from 0.1 to 140 days. using galactic kinematics as a proxy for age, we find that mid m dwarfs in the field are slowly-rotating, with periods of approximately 100 days at 5 gyr. we combine our 387 rotation period measurements and 247 new optical spectra with data from the literature. we confirm that the activity of rapidly rotating m dwarfs maintains a saturated value and our data show a clear power-law decay in relative h-alpha luminosity as a function rossby number. i will discuss planet-hosting m dwarfs in the context of the relationship between age, rotation, and activity. | age, rotation, and activity in m dwarfs and the implications for planet-hosting stars |
this presentation will review the intended purpose of the habitable zone, recent work on the habitable zone, and critical areas of work that are needed to improve the habitable zone. the habitable zone is a concept designed to help us 1) design future direct telescopes and instrumentation whose goals include confirming habitability and/or searching for biosignatures; and 2) prioritize targets with a high likelihood of habitability when using those assets. because of these intended purposes, the habitable zone has been centered around identifying regions around a star for which planets could sustain global surface liquid water over geological timescales. such planets have the highest likelihood of being not only habitable but also supporting robust biospheres that are detectable with telescopes across interstellar space. however, it is not meant to be a theoretical consideration of the range of conditions over which a planet might harbor habitable environments. it is also focuses on factors based on or inferred from past measurements. there are three things that control the habitable zone's central criterion, the sustainability of global liquid water: the temperature of the environment, the pressure of the environment, and the presence of water molecules in the environment. in the past, research on the habitable zone has focused almost exclusively on the first of these environmental control factors. and while more a ever-more complete consideration of climate feedbacks can improve our understanding of temperature controls on habitability, future work should focus the effects of atmospheric pressure and water abundance on habitability. specifically, we need to understand what controls the presence/absence of rocky planet atmospheres. this will require incorporation of expertise from space physics, astrophysics, and deep-earth/planet geology. by combining such expertise in the future, we will improve our ability to assess habitability of exoplanets on a global scale, by considering both their potential climates, and also controls on the availability of the materials that constitute planetary oceans and the atmospheres that keep them in a liquid state. such improvements have the potential for major impacts on the habitable zone's intended purpose: considerations of future space telescopes and their targets. | the habitable zone: intended applications, controversial misapplications, and needed improvements |
in the search for potentially habitable exoplanets, m-dwarf systems are particularly promising due to their abundance in the galaxy. planets orbiting these stars are likely tidally locked in 1:1 spin orbit states. this paper will examine the effects of negative carbon-silicate feedback on the climate of these tidally locked planets. recent work has shown that earth-like planets in the outer regions of the habitable zone may experience unstable climates that enter limit cycles between temperate and glaciated states. concurrently, it has been shown that tidally locked planets are unlikely to experience a bifurcation as they transition from a temperate to a glaciated state, which could inhibit these limit cycles. in this paper we run plasim, an intermediate-complexity global climate model (gcm), coupled to a carbon cycle model for tidally locked planets. we test for limit cycles at various levels of insolation and co2 outgassing flux. we should have results by december. this work is important because climate limit cycles would likely limit a planet's potential for complex life. | testing for climate limit cycles on tidally locked planets |
the three nearby tidally locked exoplanets--proxima b, trappist 1e, and lhs 1140b will be the prime targets for future atmosphere and climate observations for finding habitable systems. previous climate studies suggest that these planets would be ice-free in the sub-stellar region and ice-covered in other regions if assuming they have surface oceans. through comparing 3d climate simulations with versus without sea ice dynamics, here we show that wind-driven sea ice flows toward the sub-stellar region strongly shrink the ice-free coverages and even drive the planets into globally ice-covered snowball states. for example, previous studies shown that trappist 1e will be ice-free in the substellar region regardless of its atmosphere. after sea ice flows are included, we find that a co2 concentration of >1,000 ppmv is required to avoid it falling into a snowball glaciation. our results suggest that ice dynamics are critical for predicting the possible climates and meanwhile observational characteristics of terrestrial planets in the habitable zone around low-mass stars. | proxima b, trappist 1e, and lhs 1140b: increased ice coverages by sea ice dynamics |
the habitable exoplanet imaging mission (habex) is one of four flagship mission concepts being studied in advance of the 2020 astrophysics decadal survey. the primary goal of habex exoplanet science is to directly image and characterize rocky planets in the habitable zones of sun-like stars. in addition to the search for signs of habitability on earth-like exoplanets, habex would pursue a wide range of other exoplanet direct imaging investigations, including the study of disks and non-habitable exoplanets of various sizes and orbits, as well as a broad range of general astrophysics. in this poster, we will summarize the planned exoplanet direct imaging capabilities of habex and provide an overview of the diversity of exoplanetary system science that habex would enable. | characterizing a diversity of exoplanetary systems with habex |
habex architecture a is a 4m unobscured telescope optimized for direct imaging and spectroscopy of potentially habitable exoplanets, and also enables a wide range of general astrophysics science. the exoplanet detection and characterization drives the enabling core technologies. a hybrid starlight suppression approach of a starshade and coronagraph diversifies technology maturation risk. in this poster we assess these exoplanet-driven technologies, including elements of coronagraphs, starshades, mirrors, jitter mitigation, wavefront control, and detectors. by utilizing high technology readiness solutions where feasible, and identifying required technology development that can begin early, habex will be well positioned for assessment by the community in 2020 astrophysics decadal survey. | technology maturity for the habitable-zone exoplanet imaging mission (habex) concept |
the coronagraph is a key instrument on the large uv-optical-infrared (luvoir) surveyor mission concept. the apodized pupil lyot coronagraph (aplc) is one of the baselined mask technologies to enable 1e10 contrast observations in the habitable zones of nearby stars. both the luvoir architectures a and b present a segmented aperture as input pupil, introducing a set of random tip/tilt and piston errors, among others, that greatly affect the performance of the coronagraph instrument by increasing the wavefront errors hence reducing the instrument sensitivity. in this poster we present the latest results of the simulation of these effects for different working angle regions and discuss the achieved contrast for exoplanet detection and characterization, including simulated observations under these circumstances, setting boundaries for the tolerance of such errors. | modelling exoplanet detection with the luvoir coronagraph: aberration sensitivity and error tolerances |
nasa's exoplanet exploration program (exep) guides the development of technology that enables the direct imaging and characterization of exo-earths in the habitable zone of sun-like stars with future space observatories. here we present the 2018 exep technology gap list, an annual update to exep's list of technologies, to be advanced in the next 1-5 years. key technology gaps are starlight suppression with a coronagraph (internal occulters) or a starshade (external occulters), enabling imaging at extreme contrast (more than 10 billion) by blocking on-axis starlight, while allowing the reflected light of off-axis exoplanets be detected. building and operating a space coronagraph capable of imaging an exo-earth will require new technologies beyond those of wfirst, the first high-contrast coronagraph in space. a starshade has never been used in a space mission and requires new capabilities in precision deployment of large structures, starlight suppression, and in formation sensing and control. we review the current state-of-the-art in coronagraph and starshade technology and the performance level that must be achieved to discover and characterize earth analogs. | technology required to image and characterize an exo-earth from space |
where should we search for life in the universe? habitable zones are traditionallydetermined based on the possibility of liquid water existing on a planet but ultraviolet (uv) radiation also plays a key role.the uv habitable zoneschematic showing how the traditional habitable zones location and width changes around different types of stars. the uv habitable zone also hasdifferent locations and widths depending on the mass and metallicity of the star. [nasa/kepler mission/dana berry]besides the presence of liquid water, there are other things life may need to persist. for life as we know it, one important elementis moderate uv radiation: if a planet receives too little uv flux, many biological compounds cant be synthesized. if it receives too much, however, then terrestrial biological systems (e.g. dna) can be damaged.to determinethe most likely place to findpersistent life, we should therefore look for the region where a stars traditional habitable zone, within which liquid water is possible, overlaps with its uv habitable zone, within which the uv flux is at the right level to support life.relationship between the stellar mass and location of the boundaries of the traditional and uv habitable zones for a solar-metallicity star. din and dout denote inner and outer boundaries, respectively. zams and tms denote when the star joins and leaves the main sequence, respectively. the traditional and uv habitable zones overlap only for stars of 11.5 solar masses. [adapted from oishi and kamaya 2016]looking for overlapin a recent study, two scientists from the national defense academy of japan, midori oishi and hideyuki kamaya, explored howthe location of this uv habitable zone and that of its overlap with the traditional habitable zone might be affected by a stars mass and metallicity.oishi and kamaya developed a simple evolutional model of the uv habitable zone in stars in the mass range of 0.084 solar masses with metallicities of roughly solar metallicity (z=0.02), a tenth of solar metallicity, and a hundredth of solar metallicity.they calculate the location of the inner and outer uv habitable zone boundaries for each star at the beginning and end of its main-sequence life. they then determine the region for which the uv habitable zone and the traditional habitable zone overlap which maximizes the potential to support persistent life.the field narrowsrelationship between the stellar mass and location of the boundaries of the traditional and uv habitable zones for a star of one hundredth solar metallicity. the traditional and uv habitable zones do not overlap for stars of any mass. [adapted from oishi and kamaya 2016]oishi and kamaya find that taking the uv habitable zone into account unsurprisingly decreases the places where persistent life might be found. for solar-metallicity stars, for instance, only those stars between 1.01.5 solar masses even have overlapping traditional and uv habitable zones.as metallicity of the host star decreases, the overlapping regions decrease as well: at a metallicity of one hundredth that of the sun (z=0.0002), the uv and traditional habitable zones do not overlap for any mass star.the authors point out that this does not necessarily mean that such stars cant support life. stellar activity such as flares and coronal mass ejections can temporarily increase uv flux, possibly providing enough to make up for low steady-state flux. and oceans on planetary surfaces could shield potential life from uv flux that is too high.nonetheless, the estimates of the uv habitable zone in this study help us to narrow down the most probableplaces for findinglife in the universe.citationmidori oishi and hideyuki kamaya 2016 apj 833 293. doi:10.3847/1538-4357/833/2/293 | uv habitable zones further constrain possible life |
for the first time in human history, our generation will have the technology needed to answer one of the longest-standing questions: "are we alone?" only recently have planet-hunting programs (such as trappist, mearth, and kepler) confirmed the first earth analogues orbiting m dwarfs. however, it is unknown whether planets orbiting the most ubiquitous stars in our galaxy can support life. i will discuss the challenges and opportunities of looking for biosignatures in transiting exoplanet atmospheres at mid-infrared wavelengths and argue that the only way to answer this question is to make a measurement. in the near term, the james webb space telescope will perform preparatory observations of rocky, habitable zone exoplanets, but not until the launch of the origins space telescope (ost, one of four large mission concepts under consideration for the 2020 astrophysics decadal survey) will we have the necessary precision to detect the simultaneous presence of methane and ozone. i will present expected results from both observatories and, with an optimized observing strategy, demonstrate how ost will assess the habitability of nearby exoplanets and search for signs of life. | the mid-infrared search for life on nearby transiting exoplanets using the origins space telescope |
most of the recent detailed exoplanet studies are focused on the so-called hot jupiters, since the smaller planets remain to be difficult to observe. at the same time, low-mass planets in the habitable zone of bright stars appear to be more interesting in terms of habitability studies and the quest of an earth twin. in the last years, the kepler mission has revealed hundreds of such intermediate mass (between earth and neptune) planets, and the upcoming cheops mission accounts them as primary targets. the large number of planets so far discovered and the time-constrained nature of cheops observations indicates the need of a prioritization scheme, possibly based on the inference of the unknown planet fundamental parameters, such as the planetary radius for planets discovered with the radial velocity method. to this end, we elaborated a grid of hydrodynamic planet upper atmosphere models for planets within this range of parameters: stellar mass (0.4 - 1.3 msun), equilibrium (surface) planet temperature (300 - 2000 k), euv flux (up to 105 ergṡ cm-2 s-1), planet radius (1 - 10 earth radii) and mass (1 - 40 earth masses). interpolation over the grid provides a fast estimation of the upper atmosphere parameters for any possible target planet inside the parameter space. we will then couple the grid with planet evolution models to greatly upgrade what currently available. the grid will be made available through a dedicated web site. we will present the grid, the first results obtained from its analysis, and future plans. | target prioritization routines for cheops observations: a grid of planet upper atmosphere models |
in 2018 nasa will launch the mit-led transiting exoplanet survey satellite (tess) which has a goal of detecting terrestrial-mass planets orbiting stars bright enough for mass determination via ground-based radial velocity observations. we inferred how many exoplanets the tess mission will detect, the physical properties of these detected planets, and the properties of the stars that those planets orbit, subject to certain assumptions about the mission performance. to make these predictions we use samples of stars that are drawn from the tess input catalog candidate target list. we place zero or more planets in orbit around these stars with physical properties following known exoplanet occurrence rates, and use the tess noise model to predict the derived properties of the detected exoplanets. we find that it is feasible to detect around 1000 exoplanets, including 250 smaller than 2 earth-radii using the tess 2-min cadence data. we examined alternative noise models and detection models and find in our pessimistic model that tess will detect just 500 exoplanets. when potential detections in the full-frame image data are included, the number of detected planets could increase by a factor of 4. perhaps most excitingly, tess will find over 2 dozen planets orbiting in the habitable zone of bright, nearby cool stars. these planets will make ideal candidates for atmospheric characerization by jwst. | simulating the exoplanet yield from the transiting exoplanet survey satellite |
traditionally, the habitable zone has been defined as the distance at which liquid water could exist on the surface of a rocky planet. however, different complexity models (simplified and fast:1d, and complex and time-intense:3d) models derive different boundaries for the habitable zone. the goal of this project was to test a new intermediate complexity 2d energy balance model, add a new ice albedo feedback mechanism, and derive the habitable zone boundaries. after completing this first project, we also studied how other feedback mechanisms, such as the presence of clouds and the carbonate-silicate cycle, effected the location of the habitable zone boundaries using this 2d model. this project was completed as part of a 2017 summer reu program hosted by cornell's center for astrophysics and plantary sciecne and in partnership with the carl sagan institute. | mapping the habitable zone of exoplanets with a 2d energy balance model |
discovery of over 4700 exoplanets in our galaxy suggests that close-in rocky exoplanets in the habitable zones around magnetically active g, k and m dwarfs should be exposed to high stellar coronal x-ray and extreme uv (euv) and wind mass fluxes. kepler and tess missions have revealed frequent superflares on cool g, k and m planet hosting dwarf stars, providing a mechanism by which host stars may have profound effects on the physical and chemical evolution of exoplanetary atmospheres. solar observations indicate that energetic flares are usually accompanied by ejection of coronal magnetized plasma referred to as coronal mass ejections or cmes. as cmes propagate out from the solar corona into interplanetary space, they drive shocks. shocks are the sites of efficient acceleration of solar energetic particles (seps) to gev energies. seps can penetrate (exo)planetary atmospheres and cause significant changes in atmospheric chemistry. while stellar superflares can be directly observed and characterized in x-ray, fuv/uv, optical and radio bands, the signatures of their cme and sep counterparts remain elusive and need detail theoretical modeling. the major questions this leads to are: can we extend solar models to simulate energetic environments of young solar type stars? can we relate and scale the properties of solar/stellar superflares & associated cmes with the fluence and particle energy spectra from active k and m dwarfs? here, i will review the recent sun-as-a star observations of sunspots and associated active regions in optical, fuv, euv and x-ray bands and their implications for stellar active regions from active stars. i will describe our recent multi-observatory international project "magnetic lives of young suns" that coordinates hst-xmm-newton, tess, nicer and ground-based observations taken with cfht observations of young (0.1-0.6 gyr) solar-like (g and k type) dwarfs. these data provide critical inputs to the data-constrained three-dimensional (3d) fully thermodynamic magnetohydrodynamic (mhd) models of coronae, and winds from young solar-like stars. i will then present recent results of data-constrained 3d mhd models of superlares and cmes from young solar-like stars coupled to the kinetic models of sep events, the crucial factor for understanding of the rise of the feedstock molecules of life on early venus, earth mars and young rocky exoplanets. | recent progress in data constrained sun-as-a-star modeling of coronae, winds and eruptive events of young solar-like stars |
rocky planets located in the habitable zones around m-dwarfs are ideal targets for the search of life outside our solar system. on the one hand, in order to better understand their formation and evolution, n-body simulations were developed. the central object was assumed to be a star close to the substellar mass limit. the simulations included tidal and general relativistic effects that incorporate the contraction and evolution of the rotational period of the central object during 100 myr, as well as gas-disk interactions with a sample of protoplanetary embryos during the gas-disk lifetime. a very relevant result is that just one of the prescriptions used to treat the interactions between the gas-disk and the sample of embryos allows the survival of a close-in compact planet population of interest, located in the habitable zone of the systems with a wide range of masses from mars-like planets up to earth-like planets and close to commensurabilities. moreover, the resulting planets with semi-major axis a < 0.1 au are in agreement with the cumulative distribution of period ratio of adjacent terrestrial-like exoplanets around stars with masses m < 0.14 msun. on the other hand, in order to estimate the probability of detection of planetary systems around very low mass stars, a numerical tool in python was developed. this new tool calculates the changes in stellar flux, radial velocity and proper motion of a sample of stars due to the interaction with their planetary systems, and estimates the probability of detection of planetary systems regarding different samplings and errors associated with a given instrument or survey. a significant result is that the radial velocity method allows a high probability of planetary detection around very low mass stars, with the current and future technology. | rocky planets at the substellar mass limit |
planets interact with their host stars through gravity, radiation and magnetic fields, and for those giant planets that orbit their stars within 20 stellar radii (=0.1 au for a sun-like star), star-planet interactions (spi) are observable with a wide variety of photometric, spectroscopic and spectropolarimetric studies. at such close distances, the planet orbits within the sub-alfvénic radius of the star in which the transfer of energy and angular momentum between the two bodies is particularly efficient. the nature of magnetic spi is modeled to be strongly affected by both the stellar and planetary magnetic fields, possibly influencing the magnetic activity of both, as well as affecting the irradiation and even the migration of the planet. as we refine our observational techniques for hot jupiter systems, we can begin to extend them to other tightly orbiting stellar systems, such as smaller planets close to m dwarfs where the region near tens of stellar radii begins to coincide with the classical habitable zone. future studies of spi with space-based telescopes and the next generation of ground-based telescopes will be informative pursuits for the study of the internal dynamics and atmospheric evolution of exoplanets. | a review and preview of magnetic star-planet interactions |
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☉ to the hydrogen-burning limit of about 0.075 m☉. 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 probability 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 |
in the next decades, ground-based direct imaging capabilities at mid-infrared wavelengths will be needed alongside jwst in order to image planets close to their stars – including most nearby habitable-zone planets. the eso/breakthrough-sponsored new earths in the alpha centauri region (near) program on the vlt recently completed the first ultra-deep imaging campaign in the mid-ir and demonstrated the first sensitivity to habitable-zone sub-neptune- sized planets. in this talk, i will describe our on-going efforts to upgrade the mid-infrared capabilities of the lbt based on the lessons from near, which will enable coordinated deep explorations for low-mass habitable-zone planets in both the northern and southern skies. i will also discuss our key observational program: lessons: the lbt exploratory survey for super-earths/sub-neptunes orbiting nearby stars. finally, i will discuss the potential scientific and societal benefits of imaging nearby habitable-zone exoplanets. | mid-infrared imaging of habitable-zone exoplanets with lbti |
editors note: in these last two weeks of 2022, well be looking at a few selections that we havent yet discussed on aas nova from among the most-downloaded articles published in aas journals this year. the usual posting schedule will resume in january.system architecture and planetary obliquity: implications for long-term habitabilitypublished september 2022main takeaway:pam vervoort (university of california, riverside) and collaborators used n-body simulations and climate models to study how the presence of a jupiter-like planet affects the long-term habitability of an earth-like planet in the same planetary system. the teams simulations showed that if jupiters orbit were more elliptical, more of earths surface might be habitable than it is today.why its interesting:with the number of confirmed exoplanets now above 5,000, many astronomers have switched from finding planets to characterizing them. among the possible characterizations of an exoplanet is determining if its within its host stars habitable zone. while the concept of the habitable zone is simple and its straightforward to estimate if a planet is currently in a stars habitable zone based on the luminosity of the star and the orbital distance of the planet the actual location of a stars habitable zone is expected to change over time. as stars age, their luminosity changes, and the dynamics of multi-planet systems can shift a planets orbital distance. vervoort and collaborators simulations provide a way to estimate the impacts of some of these changes.how a neighboring jupiter-like planet affects habitability:sea ice cover, eccentricity (how elliptical the orbit is), and obliquity (how tilted the planet is), and fractional habitability of an earth-like planet in a system with a jupiter-like planet with varying orbital parameters. click to enlarge. [vervoort et al. 2022]jupiter is often credited with helping to keep earth habitable by redirecting certain comets safely out of the inner solar system, for example but is the largest planet in our solar system as helpful as it could be? not so, say vervoort and collaborators. the teams simulations show that earths habitability (as measured by the fraction of the planet with a hospitable air temperature and no sea ice) would be higher if jupiters orbit were significantly more elliptical than it is today. while we wont be coaxing jupiter into a more elliptical orbit to boost earths habitable area anytime soon, the results of this study can inform our investigations of potentially earth-like planets around other stars, helping us to discern which of the growing population of exoplanets might be habitable.citationpam vervoort et al 2022 aj 164 130. doi:10.3847/1538-3881/ac87fdthe post selections from 2022: would changing jupiters orbit affect earths habitability? appeared first on aas nova. | selections from 2022: would changing jupiter's orbit affect earth's habitability? |
observing earth-like exoplanets orbiting within the habitable zone of sun-like stars and studying their atmospheres in reflected starlight requires contrasts of ~10-10 in the visible. at such high contrast, starlight reflected by exozodiacal dust is expected to be a significant source of contamination. here, we present high-fidelity simulations of coronagraphic observations of a synthetic solar system located at a distance of 10 pc and observed with a 12 m and an 8 m circumscribed aperture diameter space telescope operating at 500 nm wavelength. we explore different techniques to subtract the exozodi and stellar speckles from the simulated images in the face-on, the 30 deg inclined, and the 60 deg inclined case and quantify the remaining systematic noise as a function of the exozodiacal dust level of the system. we find that in the face-on case, the exozodi can be subtracted down to the photon noise limit for exozodi levels up to ~1000 zodi using a simple toy model for the exozodiacal disk, whereas in the 60 deg inclined case this only works up to ~50 zodi. we also investigate the impact of larger wavefront errors and larger system distance, finding that while the former have no significant impact, the latter has a strong (negative) impact. ultimately, we derive a penalty factor as a function of the exozodi level and system inclination that should be considered in exoplanet yield studies as a realistic estimate for the excess systematic noise from the exozodi. | impact and calibration of exozodiacal dust on observations of earth-like planets with a large future ir/o/uv space telescope |
the habitable exoplanet observatory (habex) is one of four mission concepts under study for the 2020 astrophysics decadal survey. its goal is to directly image and spectroscopically characterize planetary systems in the habitable zone around nearby sun-like stars. additionally, habex will perform a broad range of general astrophysics science enabled by 115 to 2500 nm spectral range and 3 x 3 arc-minute fov. critical to achieving the habex science goals is a large, ultrastable uv/optical/near-ir (uvoir) telescope. the baseline habex telescope is 4-meter off-axis unobscured, diffraction limited at 400 nm with wavefront stability on the order of a few 10s of picometers. the technology readiness level (trl) to manufacture and test the habex baseline primary mirror is assessed to be at trl-6 for all but two trl-4 technologies: 1) non-destructive process to quantify cte homogeneity of a 4-m mirror substrate with a spatial sampling of at least 100 x 100 to better than +/- 1 ppb/k; and, 2) process to quantify self-weight gravity deflection to better than 4-nm rms over a 100 x 100 spatial sampling. this paper reviews the technology needs to manufacture the habex primary mirror, assesses their trl and proposes a roadmap to mature the two remaining technologies to trl-6. | technology development roadmap for habitable-zone exoplanet observatory (habex) baseline 4-m primary mirror |
lhs 1140b is a terrestrial exoplanet orbiting in the habitable zone of an m4.5 star (dittmann et al. 2017b; ment et al. 2019). from radial velocity measurements of its mass and transit measurements of its radius, we know that lhs 1140b has a rocky composition, though its radius of 1.7 earth radii puts it at the upper limit of the population of rocky worlds (fulton et al. 2017). it is an open question whether or not temperate terrestrial planets orbiting low-mass stars can retain atmospheres. the exploratory investigation we present here aims to put upper limits on what we can achieve with ground-based observatories to answer this question. this investigation faced challenges: the 25-day orbital period and 2-hour transit duration of lhs 1140b means that there are few observable transits per year from any single observing location. over the course of 2017 and 2018 we observed two transits of lhs1140b, each time using both 6.5 m magellan telescopes at las campanas observatory simultaneously. we used the multi-object spectrographs ldss3c and imacs to produce a transmission spectrum from 610-1030 nm. the residuals in our data are within 1.5× the photon-noise limit. this data set is not sufficient for us to test realistic models of the atmosphere of lhs 1140b, owing to its cool equilibrium temperature (235 k), high surface gravity (23.7 m/s2), and likely high mean molecular weight composition. alternatively, if we can identify a system similar to lhs 1140 (i.e., having a terrestrial planet orbiting in the habitable zone of a mid-m star) but at a distance of 5 pc and with the earth's surface gravity, an atmospheric detection could be achieved in as few as 8 transits, depending on the atmospheric composition. in the era of extremely large telescopes (elts), we may be able to access the atmospheres of hard-to-reach planets like lhs 1140b. hdl is supported by an nsf graduate research fellowship. this work is supported by a grant from the john templeton foundation. | limits on the atmosphere of a habitable-zone terrestrial planet from ground-based spectroscopy |
accurate measurement of exoplanetary masses is a critical step in addressing key aspects of nasa's science vision. new technologies to implement an astrometric instrument capable of measuring masses of earth-analog planets aboard as a part of nasa's future mission portfolio will be required: this is simply the only viable avenue to attaining these data. here we propose to advance diffractive pupil (dp) technology, capable of performing mass measurements down to 1 earth mass, to trl-5. this will immediately empower the possibility for dedicated astrometric missions, and perhaps most enticing, it will enable astrometric observing modes to be added (with relatively low cost and impact) to any mission boasting a sufficiently stable direct imaging platform. astrometry is the only technique that can unequivocally measure exoplanet masses regardless of the system alignment, and serves to independently confirm direct imaging detections, yielding more precise planet orbits than direct imaging alone. most critically, detection noise floors make it uniquely suited to habitable zone orbits for earth-mass objects around sun-like stars: true earth-analogs. therefore, this technology can confer unique scientific benefits to future flagship missions. in particular, because these missions are expected to yield one or two dozen exoearths, measurements of mass add very significant value to the science of habitability in the solar neighborhood. the proposed work has three areas that complement each other to develop an efficient and reliable technology: 1) data reduction and calibration algorithms will be fully developed (including those for a diffractive pupil optimized for single and binary stars). to fully benchmark the methodology, confronting the signal recovery with real data from an optical laboratory testbench is essential. 2) a prototype instrument that performs an end-to-end astrometry demonstration in air and in vacuum will be built and tested. this astrometric instrument will include a star simulator with capability to inject simulated planetary orbital signals, together with a telescope equipped with a diffractive pupil, and laser metrology for detector calibration. 3) a study of implementation aboard the habex mission in which the diffractive pupil is implemented at an intermediate location in the optical path (not on the telescope primary mirror) will be performed. such a scenario calls for calibration of the upstream path by way of the telescope metrology system. during year 1 we will improve existing distortion calibration algorithms (ames and sydney) and integrate and test the instrument in air at ames. in parallel, jpl will build the laser metrology system and calibrate the camera. during year 2 the data reduction pipeline will be tested using real data, and the instrument moved to jpl where the laser metrology will be integrated and the system ready for full vacuum testing. in parallel, the habex implementation analysis will be initiated. in year 3, vacuum tests will be undertaken at jpl, while simultaneously the habex analysis will be finalized. this proposal leverages successful execution of apra-09 and tdem-13 that brought the dp technology to trl-4. ames research center and jpl will partner for the execution of this proposal utilizing previous investments and expertise in laser metrology from jpl and distortion calibration at ames. | enabling imaging astrometry detection and mass measurement of earth-like planets |
i present a catalog of 1,794 stellar evolution models for solar-type and low-mass stars, which is intended to help characterize real host-stars of interest during the ongoing search for potentially habitable exoplanets. the main grid is composed of 904 tracks, for 0.5-1.2 m solar masses at scaled metallicity values of 0.1-1.5 z solar masses and specific elemental abundance ratio values of 0.44-2.28 o/fe solar masses, 0.58-1.72 c/fe solar masses, 0.54-1.84 mg/fe solar masses, and 0.5-2.0 ne/fe solar masses. the catalog includes a small grid of late stage evolutionary tracks (25 models), as well as a grid of m-dwarf stars for 0.1-0.45 m solar masses (856 models). the time-dependent habitable zone evolution is calculated for each track, and is strongly dependent on stellar mass, effective temperature, and luminosity parameterizations. i have also developed a subroutine for the stellar evolution code tycho that implements a minimalist coupled model for estimating changes in the stellar x-ray luminosity, mass loss, rotational velocity, and magnetic activity over time; to test the utility of the updated code, i created a small grid (9 models) for solar-mass stars, with variations in rotational velocity and scaled metallicity. including this kind of information in the catalog will ultimately allow for a more robust consideration of the long-term conditions that orbiting planets may experience. in order to gauge the true habitability potential of a given planetary system, it is extremely important to characterize the host-star's mass, specific chemical composition, and thus the timescale over which the star will evolve. it is also necessary to assess the likelihood that a planet found in the "instantaneous" habitable zone has actually had sufficient time to become "detectably" habitable. this catalog provides accurate stellar evolution predictions for a large collection of theoretical host-stars; the models are of particular utility in that they represent the real variation in stellar parameters that have been observed in nearby stars. | the diversity of chemical composition and the effects on stellar evolution and planetary habitability |
the high energy x-ray and uv radiation fields of host stars play a crucial role in determining the atmospheric conditions and habitability of potentially-habitable exoplanets. this paper focuses on the major surveys of the uv/x-ray emissions of m- and k-type exoplanet hosts that have been undertaken by the muscles and megamuscles hubble space telescope (hst) treasury programs and associated contemporaneous x-ray and ground-based observations. the quiescent and flaring radiation (both photons and implied particles) were observed from this extensive sample of relatively old, low mass, exoplanet host stars and show that, from the viewpoint of a habitable-zone exoplanet, there is no such thing as an "inactive" m dwarf star. the resulting implications are significant for planetary habitability. extensive monitoring of the x-ray/uv emission from a representative younger m dwarf is also presented and the direct stellar effects that influence exoplanets during the earlier phases of their formation and evolution discussed. | the uv/x-ray radiation fields and particle (cme) flows of m dwarf exoplanet host stars |
successfully launched in april 2018, nasa's transiting exoplanet survey satellite (tess) is well on its way to discovering thousands of exoplanets in orbit around the brightest stars in the sky. during its initial two-year survey mission, tess has monitored more than 200,000 targeted bright stars in the solar neighborhood for drops in brightness caused by planetary transits. this first-ever spaceborne all-sky transit survey mission is identifying planets ranging in size from earth-sized to gas giants, orbiting a wide variety of host stars, from cool m dwarfs to hot o/b giants. tess stars are typically 5-10 times closer (thus 25 -100 times brighter) than those surveyed by the kepler satellite; hence tess planets are proving far easier to characterize with follow-up observations than those from prior missions. such tess followup observations have already enabled measurements of the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including habitable zone rocky worlds. an additional data product from the tess mission is its full frame images (ffis), which were collected at a cadence of 30 minutes in the just-completed primary mission. these ffis provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the tess cameras. in total, nearly 100 million objects brighter than magnitude i = +16 were precisely photometered during the two-year prime mission. tess completed its southern ecliptic hemisphere survey in july 2019, and will complete its northern ecliptic hemisphere survey in july 2020. a concurrent, two year-long deep survey by tess of regions surrounding the north and south ecliptic poles is providing prime exoplanet targets for characterization with the james webb space telescope (jwst), as well as with other large ground-based and space-based telescopes coming online during the next two decades. tess received the top science ranking for operating explorer missions in the 2019 nasa astrophysics senior review, assuring that the mission will be extended through at least 2022. in principle, tess's unique lunar-resonant orbit should facilitate additional extended missions lasting more than a decade. the status of tess and its exoplanet yield as it completes its primary mission survey will be reviewed. during the upcoming extended mission, tess will have even more powerful operating modes, including a new 20 second target cadence. the ffi cadence will accelerate from 30 minutes to 10 minutes. in addition, there will be even more emphasis on community engagement, with 8 times as many guest investigator-selected 2 minute cadence targets. the sky coverage and re-visit plans for the extended mission will also be presented. | review of tess's primary mission and plans for continuing sky surveys |
the success of the keck telescopes' segmented mirror technology provided a basis for the development of other large and extremely large telescopes. we investigate ways to optimize the performance of the segmented mirror telescope further to (1) take on the challenges of high contrast imaging to characterize habitable zone exoplanets, (2) enable visible adaptive optics (ao), and (3) fully benefit from recent extreme ao developments. the current status of keck telescope phasing using the phasing camera system (pcs) is briefly presented. a phase retrieval technique is presented that uses ao science instrument images to improve the phasing of the telescope primary mirror. the technique was tested on the keck telescopes, and the first experimental results are presented along with the limitations of this approach. the static, semi-static, and dynamic nature of the residual segment piston errors are discussed, along with possible elevation-dependent residual segment piston errors. we propose that the technique be periodically used at keck observatory to monitor and improve telescope phasing. we discuss the significance of the technique for ao observations with the existing and future large aperture optical telescopes. the ultimate goal is to push large aperture ground-based telescopes to their performance limits and make them competitive with space telescopes in terms of psf stability to enable breakthrough science. | a phase retrieval technique to measure and correct residual segment piston errors of large aperture optical telescopes |
the large majority of stars in the milky way are late-type dwarfs, and the frequency of especially low-mass exoplanets in orbits around these late-type dwarfs appears to be high. in order to characterize the radiation environments and habitable zones of the cool exoplanet host stars, stellar radius and effective temperature, and thus luminosity, are required. it is in the stellar low-mass regime, however, where the predictive power of stellar models is often limited by sparse data quantity with which to calibrate the methods. we show results from our chara survey that provides directly determined stellar parameters based on interferometric diameter measurements, trigonometric parallax, and spectral energy distribution fitting. | characterizing the parents: exoplanets around cool stars |
understanding whether m-dwarf stars may host habitable planets with earth-like atmospheres and biospheres is a major goal in exoplanet research. if such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. here, we consider stellar activity of m-dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (n2), which leads to production of nitrogen oxides in the planetary atmosphere, hence affecting biomarkers such as ozone. we apply a stationary model, that is, without a time-dependence, hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. this point should be further explored in future work with time-dependent models. for the flaring case o3 is mainly destroyed via direct titration with nitrogen oxides and not via the familiar catalytic cycle photochemistry, which occurs on earth. for scenarios with low o3, rayleigh scattering by the main atmospheric gases became more important for shielding the planetary surface from ultra-violet radiation. a major result of this work is that the biomarker o3 survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker nitrous oxide could survive in the planetary atmosphere under all conditions of stellar activity considered here, which clearly has important implications for missions that aim to detect spectroscopic biomarkers. | response of atmospheric biomarkers to nox-induced photochemistry generated by stellar cosmic rays for earth-like planets in the habitable zone of m-dwarf stars |
the habitable exoplanet imaging mission (habex) is a candidate flagship mission being studied by nasa and the astrophysics community in preparation of the 2020 decadal survey. the habex mission concept is a large (~4 to 6.5m) diffraction-limited optical space telescope, providing unprecedented resolution and contrast in the optical, with likely extensions into the near uv and near infrared domains. we discuss the primary science goals of habex. first, habex will survey a large sample of stars to search for planets potentially habitable planets: roughly earth-sized planets with separations consistent with being in the habitable zones of their parent stars. promising candidates will be followed up in detail, in order to characterize their orbits and atmospheres, and so confirm that they are indeed terrestrial-sized planets in the habitable zones of their parent stars, and search for signatures of habitability and potentially biosignatures. second, habex will perform a ‘deep dive’ survey of roughly a dozen of the nearest and most promising stellar systems, providing the first complete “family portraits” of planets around our nearest sun-like neighbors, and placing the solar system in the context of a diverse set of these planetary systems. additionally, habex will enable a wide range of other astrophysical investigations, including detailed characterization of the properties of nearby stars and galaxies. | the habitable exoplanet imaging mission (habex) |
exoplanet imaging has thus far enabled studies of wide-orbit (>~10 au) giant planet (>~2 jupiter masses) formation and giant planet atmospheres, with future 30 meter-class extremely large telescopes (elts) needed to image and characterize terrestrial exoplanets. however, current state-of-the-art exoplanet imaging technologies placed on elts would still miss the contrast required for imaging earth-mass habitable-zone exoplanets around low-mass stars by 100x due to speckle noise-scattered starlight in the science image due to a combination of aberrations from the atmosphere after an adaptive optics (ao) correction and internal to the telescope and instrument. we have been developing a focal plane wavefront sensing technology called the fast atmospheric self-coherent camera technique (fast) to address both of these issues; in this work we present the first results of simultaneous first and second stage ao wavefront sensing and control with a shack hartmann wavefront sensor (shwfs) and fast, respectively, using two common path deformable mirrors. we demonstrate this "multi-wfs single conjugate ao" real-time control at up to 200 hz loop speeds on the santa cruz extreme ao laboratory (seal) testbed, showing a promising potential for both fast and similar high-speed diffraction-limited second-stage wavefront sensing technologies to be deployed on current and future observatories, helping to remove speckle noise as the main limitation to elt habitable exoplanet imaging. | first laboratory demonstration of real-time multi-wavefront sensor single conjugate adaptive optics |
transit spectroscopy of terrestrial planets around nearby m dwarf stars is a primary goal of space missions in the coming decades. 3d climate modeling has shown that slowly rotating terrestrial extrasolar planets, at the inner edge of their habitable zones (ihz), may possess significantly enhanced stratospheric water vapor compared to a rapidly rotating planet like earth. for host m-dwarfs with teff > 3000 k, synchronously rotating ihz planets have been shown to retain moist greenhouse conditions (stratospheric water mixing ratio >10-3) despite low earth-like surface temperatures. in such slow rotators, strong vertical mixing is expected to loft the h2o high into the atmosphere. this is promising for h2o detection in the atmospheres of tidally-locked habitable planets with the upcoming james webb space telescope (jwst). the first hz exoplanets to have their atmospheres characterized will likely be such tidally-locked planets orbiting nearby m dwarfs. however, m dwarfs also possess strong uv activity, which may effectively photolyze stratospheric h2o. prior modeling efforts have not included the impact of high stellar uv activity on stratospheric h2o abundance. here, we employ a 1-d photochemical model with varied stellar uv, to assess whether h2o destruction driven by high stellar uv would affect the detectability of h2o in transmission spectroscopy. temperature and water vapor profiles are taken from published 3-d climate model simulations for an inner hz earth-sized planet around a 3300 k m dwarf with a pure n2-h2o atmosphere; they serve as self-consistent input profiles for the 1-d model. we find that as long as the atmosphere is well-mixed up to the 1 mbar pressure level, uv activity appears to not impact detectability of h2o in the transmission spectrum. the strongest h2o features occur in the jwst miri instrument wavelength range and are comparable to the estimated systematic noise floor of ~50 ppm for a cloudless atmosphere. we also explore additional chemical complexity within the 1-d model by introducing other species into the atmosphere and discuss their impact on the transmission spectrum. | the impact of stellar uv activity on habitable moist terrestrial exoplanet atmospheres around m dwarfs |
future space-based direct imaging missions (habex, luvoir) would observe reflected light off rocky exoplanets in the habitable zones of sun-like stars. the ultimate goal of these concept missions is to characterize the planets we detect, but the spectroscopic measurements required for that are quite costly. therefore, to vet the best spectroscopy targets, one should leverage all the information available a priori. there are two ways in which knowing an exoplanet's orbit would help: (i) the orbit's semi-major axis informs whether the planet might possibly harbour liquid surface water, making it a peak-curiosity target; and (ii) predicting the planet's future location would tell us where and when to look. the science yields of habex and luvoir should therefore depend on the number, cadence, and precision of observations required to establish the orbit of a planet within its star's habitable zone. we quantify these statistically: using markov chain monte carlo methods, we fit the six keplerian orbital parameters to mock direct imaging data for hundreds of simulated planets, and retrieve the parameters' average precisions as functions of cadence, number of epochs, distance to target, and astrometric error. because each image returns two data (the x and y positions), at most three epochs should be required to fit all six parameters. however, we find that less than three epochs could place an earth twin planet within the habitable zone at 1-sigma confidence. | determining orbits of directly imaged exoplanets within the habitable zone |
the philosophy of the habex design favors as high a technology readiness level (trl) as possible to minimize risk. we discuss the habex technology requirements and state of the art to assess the current trl and provide roadmaps to trl 5. | technology roadmap for the habitable-zone exoplanet observatory (habex) concept |
molecular oxygen (o2) has long been debated as a potentially important bio-signature in observations of exoplanetary atmospheres. at earth, substantial o2 occurs as a result of photosynthetic production. however, a variety of circumstances have been proposed as capable of producing abiotic build-up of o2 for habitable zone planets through extreme water loss, including super luminous pre-main sequence phases or a deficit of non-condensible gas content. in these situations, thermal escape of photolysed hydrogen leaves behind large amounts of o2. while such processes are likely very important to the evolution of the planetary atmosphere, non-thermal escape processes such as ion escape are also important and have played a critical role in altering the composition of the atmospheres of both mars and venus. here we evaluate the ability of the escape of o+ to inhibit abiotic build-up during extended pre-main sequence phase water loss for venus-like planets around stars of different masses. we use a combination of analytic estimations and simple models to evaluate the state of the upper atmosphere, production of o+ ions, and subsequent escape rates as a function of stellar luminosity and wind. we then predict the co-evolution in time of the hydrogen and oxygen escape, in order to assess the degree to which oxygen build-up occurs and the timescales over which it would be observable. we show that during the extreme stellar conditions responsible for driving rapid water loss substantial non-thermal escape of o+ also occurs, which can inhibit o2 build-up. | does non-thermal escape inhibit abiotic o2 build-up? |
it is very difficult to detect oxygen around earth-like exoplanets even by using a large ground-based telescope or jwst in visible to near infrared. uv spectroscopy will reveal the expanded atomic oxygen upper atmosphere around an earth-like exoplanet in the habitable zone of a low temperature star. | observability of oxygen exosphere of an earth-like exoplanet around a low temperature star |
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 8m ⊕ 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 coplanar, 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 <math xmlns:xlink="http://www.w3.org/1999/xlink"> <mi>m</mi> <mo>sin</mo> <mi>i</mi> m \sin 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. | cancri (copernicus): a multi-planet system with a hot super-earth and a jupiter analogue |
m dwarfs have much longer main sequence lifetimes than the sun and provide stable habitable zones for tens of billions of years, perhaps making m dwarf planets some of the most habitable in the galaxy. additionally, the smaller radii of m dwarfs allow us to more easily detect transiting earth-analog planets, due to the higher planet/star radius ratio of the system than of fgk stars. we seek to better understand the m dwarfs (known and new) in the kepler field, using the wealth of information provided by the kepler. we confirm a sample of m dwarfs using the crossmatch between the initial kepler dataset and the second gaia data release. we calculate the spectral energy distributions (seds) of these objects, using distances from gaia and available archival photometry (e.g., allwise, 2mass, sdss, and panstarrs). we use the seds to measure updated luminosities, temperatures, masses and radii using empirically based calculations for these stars, rejecting those that don't qualify as m dwarfs. using kepler light curves, we calculate rotation rates of these stars and compile, hα, uv, x ray and flare rate information from archival surveys. we show that white light (kepler bandpass, kp) flare strength is highly correlated with rotation rate for m dwarfs and that m dwarfs with fast rotation rates and higher flare strengths in the initial kepler dataset do not have any confirmed exoplanet detections. while the majority of the stars that we investigate have no confirmed exoplanet detections, a small part of this subsample are known to host transiting exoplanets. we measure updated planetary radii and equilibrium temperatures for these transiting exoplanets. comparing stellar populations with and without confirmed planets will allow us to examine how m dwarf magnetic strength and activity impact planetary occurrence. | expanding our understanding of m dwarfs in the kepler field |
as the first known multi-planet system of earth-sized worlds, the trappist-1 system has been the subject of intense study since its discovery. with at least three of its planets in the traditional habitable zone, the trappist-1 system offers an exceptional opportunity to study the evolution, potential habitability, and possible aerosol formation of planetary atmospheres around m-dwarf stars. using a combination of laboratory results for temperate exoplanet atmospheres and a 1-d atmospheric model, we explored the feasibility of aerosols in hydrogen-rich atmospheres to explain the featureless hubble space telescope (hst) transmission spectra of trappist-1 d, e, f, and g. from the laboratory, we have constraints on haze particle size and production rate. using these constraints as a guideline, we found that based on physically realistic haze formation scenarios, trappist-1 d and e likely do not have hydrogen-rich atmospheres with hazes muting spectroscopic features. we also investigated the effect of an opaque cloud layer in hydrogen-rich atmospheres: high altitude clouds are needed in these models to explain the hst transmission spectra for trappist-1 d and e. at the required altitudes, it is unlikely that an optically thick cloud could form due to the lack of material available. finally, i will present lower limits for the mean molecular weights of the trappist-1 atmospheres, both with and without an opaque cloud deck. current observational precision is not yet strong enough to rule out extended hydrogen-rich atmospheres for trappist-1 f and g, and these worlds will require follow-up with more powerful observatories, such as the james webb space telescope. our findings support secondary rather than primordial atmospheres for the trappist-1 planets and allow for substantial evolution of these atmospheres over their lifetimes, as found in previous studies. beyond the trappist-1 system, this study has broader implications for other m-dwarf hosted terrestrial planets, which should also be expected to have secondary rather than primordial, hydrogen-rich atmospheres. | limits on clouds and hazes in the trappist-1 planets: insights from the laboratory and models |
background: among the ≈4000 confirmed exoplanets, most of them are orbiting around m dwarfs because they are relatively easy to detect and m dwarfs are the most common type of star in the galaxy. about 15 exoplanets are most likely to have rocky compositions and meanwhile in the habitable zone within which the surface is temperate to maintain liquid water. these planets are the prime targets for future atmospheric characterizations of potentially habitable systems, especially the three nearby ones-proxima b, trappist-1e, and lhs 1140b. previous studies suggest that if these planets have surface ocean they would be in an eyeball-like climate state: ice-free in the vicinity of the substellar point and ice-covered in the rest regions. however, an important component of the climate system-sea ice dynamics has not been well studied in their work. fundamental question: would the open ocean of the eyeball-like climate be stable against a globally ice-covered snowball state? or, could sea-ice drift close the open ocean? methods: through a series of climate experiments, we investigate the effects of oceanic heat transport and sea-ice drift on the surface ice coverage of tidally locked terrestrial planets. hundreds of numerical experiments were performed in order to clearly know the robustness of the results. conclusion: ocean dynamics trend to expand the open-ocean area, but more importantly wind-driven sea-ice drift toward the substellar point shrinks the open-ocean area and even drives some of them to a snowball state. this works for both a synchronous orbit and a resonance orbit. the dominated mechanism is that sea-ice drift cools the sea surface through absorbing heat during ice melting when the ice flows to the warmer substellar region. implication: previous studies have shown that stellar radiation, atmospheric composition and evolution, atmosphere dynamics, clouds, and ocean dynamics are important for the climate and habitability of tidally locked planets. here, we show that another critical factor—sea ice dynamics, which is able to drive an eyeball-like climate state to a globally ice-covered snowball state. | transition from eyeball to snowball driven by sea-ice drift on tidally locked terrestrial planets |
the first exoplanets were discovered in the years leading up to the launch of xmm-newton. this was well after the design had been completed. further, the effect of xuv photons on possible exoplanets had hardly been considered when xmm-newton launched. nonetheless, xmm-newton has been instrumental in informing our understanding of exoplanets, their atmospheres, habitable zones and how they interact with their host stars. in this presentation i highlight the contributions to exoplanet science made by xmm-newton (sometimes in collaboration with the chandra x-ray observatory) over the last two decades. this research has included many individual exceptional system such as corot-2, hd17156 and gj436. conversely, so many x-ray bright exoplanet hosts have been identified that statistical analysis, such the distribution of exoplanet masses in the presence of x-ray irradiation, are possible. as an example i discuss results that suggests that planet atmospheres have been eroded by their host star coronal emissions (e.g. sanz-forcada 2010, owen & lai 2018). i finish with a discussion of prospects for observations with xmm-newton over the next decade and with future missions. | 20 years of x-ray exoplanet observations |
one of the primary goals of exoplanet-hunting missions like kepler is to discover earth-like planets in their hosts habitable zones. but could there be other relevant worlds to look for? a new study has explored the possibility of habitable moons around giant planets.seeking rocky worldssince its launch, the kepler mission has found hundreds of planet candidates within their hosts habitable zones the regions where liquid water can exist on a planet surface. in the search for livable worlds beyond our solar system, it stands to reason that terrestrial, earth-like planets are the best targets. but stand-alone planets arent the only type of rocky world out there!many of the kepler planet candidates found to lie in their hosts habitable zones are larger than three earth radii. these giant planets, while unlikely to be good targets themselves in the search for habitable worlds, are potential hosts to large terrestrial satellites that would also exist in the habitable zone. in a new study led by michelle hill (university of southern queensland and university of new england, australia; san francisco state university), a team of scientists explores the occurrence rate of such moons.kepler has found more than 70 gas giants in their hosts habitable zones. these are shown in the plot above (green), binned according to the temperature distribution of their hosts and compared to the broader sample of kepler planet candidates (grey). [hill et al. 2018]a giant-planet tallyhill and collaborators combine the known kepler detections of giant planets located within their hosts optimistic habitable zones with calculated detection efficiencies that measure the likelihood that there are additional, similar planets that were missing. from this, the authors estimate the frequency with which we expect giant planets to occur in the habitable zones of different types of stars.the result: a frequency of 6.5 1.9%, 11.5 3.1%, and 6 6% for giant planets lying in the habitable zones of g, k, and m stars, respectively. this is lower than the equivalent occurrence rate of habitable-zone terrestrial planets which means that if the giant planets all host an average of one moon, habitable-zone rocky moons are less likely to exist than habitable-zone rocky planets. however, if each giant planet hosts more than one moon, the occurrence rates of moons in the habitable zone could quickly become larger than the rates of habitable-zone planets.lessons from our solar systemdistribution of the estimated planetmoon angular separation for known kepler habitable-zone giant planets. future missions would need to be able to resolve a separation between 1 and 90 microarcsec to detect potential moons. [hill et al. 2018]what can we learn from our own solar system? of the 185 moons known to orbit planets within our solar system, all but a few are in orbit around the gas giants. jupiter, in particular, recently upped its tally to a whopping 79 moons! gas giants therefore seem quite capable of hosting many moons.could habitable-zone moons reasonably support life? jupiters moon io provides a good example of how radiative and tidal heating by the giant planet can warm a moon above the temperature of its surroundings. and jupiters satellite ganymede demonstrates that large moons can even have their own magnetic fields, potentially shielding the moons atmospheres from their host planets.overall, it seems that the terrestrial satellites of habitable-zone gas giants are a valuable target to consider in the ongoing search for habitable worlds. hill and collaborators work goes on to discuss observational strategies for detecting such objects, providing hope that future observations will bring us closer to detecting habitable moons beyond our solar system.citationexploring kepler giant planets in the habitable zone, michelle l. hill et al 2018 apj 860 67. doi:10.3847/1538-4357/aac384 | habitable moons instead of habitable planets? |
the transiting exoplanet survey satellite (tess) has so far discovered a multitude of potentially habitable planet candidates. the next step in confirming the habitability of these exoplanets will be spectroscopic observations by the next generation of telescopes. in an effort to prioritize candidates for these observations, i have calculated the earth similarity index (schulze-makuch, d. et al., 2011) for each of the planet candidates identified by tess that are within the habitable zones of their host stars. as tess data is based on transit observations and not radial velocity measurements, the density of the planets used in the calculations is obtained using the mass-radius relationship created by ning, b. et al. (2018) which in turn is based on data taken from the kepler mission. overall, 3 were found to have a global esi greater than 0.8, indicating an earth-like planet, though 11 had global esis between 0.7, the esi of mars and 0.8. | a survey of the habitability of tess planet candidates |
with a radius of 0.95 rearth and a mass of 0.85 mearth, venus is the most analogous planet to earth in the solar system. study of venus and venus-like exoplanets is invaluable in understanding factors that determine a planet's habitability throughout its evolution. fortunately, many venus-analogs are expected to soon be discovered as the recently launched transiting exoplanet survey satellite (tess) mission is sensitive to planets in close proximity to their host stars. tess is predicted to discover hundreds of terrestrial planets within the inner boundary of their host star's habitable zone (hz), placing them in the 'venus zone' (vz), defined by kane et al. (2014). tess in tandem with the launch of the james webb space telescope in the coming years will allow for the characterization of these planets' atmospheres, providing a better understanding of atmospheric compositions of planets inside the vz. this will help delineate the primary factors that determine whether a planet develops sustainable temperate surface conditions, or if it would be pushed into a runaway greenhouse state, leading to a more well-defined outer boundary for the vz. here we provide a progress report on discoveries from the tess mission, identification of planets in the vz, and methods used to determine runaway greenhouse scenarios. the observed properties of these planets will be applied to global climate models, such as rocke-3d, to better constrain the boundaries of the hz and vz, and study the atmospheric demographics of terrestrial planets. | identifying potential venus analogs from exoplanet discoveries |
we analyzed radial velocity data from the carmenes vis channel, hires/keck, and harps. all the rvs are corrected for barycentric motion and secular acceleration. the carmenes measurements were taken in the context of the carmenes search for exoplanets around m dwarfs. the carmenes instrument consists of two channels: the vis channel obtains spectra at a resolution of r=94600 in the wavelength range 520-960nm, while the nir channel yields spectra of r=80400 covering 960-1710nm. both channels are calibrated in wavelength with hollow-cathode lamps and use temperature- and pressure-stabilized fabry-perot etalons to interpolate the wavelength solution and simultaneously monitor the spectrograph drift during nightly operations (bauer et al., 2015a&a...581a.117b). (1 data file). | vizier online data catalog:a neptune-mass planet traversing the habitable zone around hd 180617 (kaminski+, 2018) |
the large ultra violet-optical-infrared (luvoir) surveyor is one of four mission concepts being studied by nasa in preparation for the 2020 astrophysics decadal survey. luvoir is a general-purpose space-based observatory with a large aperture in the 8-15 m range and a total bandpass spanning from the far-ultra violet to the near-infrared. one of luvoir's main science objectives is to directly image temperate earth-sized planets in the habitable zones of sunlike stars, measure their spectra, analyze the chemistry of their atmospheres, and obtain information about their surfaces. this direct imaging of exoplanets is enabled by luvoir's extreme coronagraph for living planet systems (eclips). luvoir can also observing potentially habitable exoplanets transiting nearby m dwarf stars. such observations will allow us to evaluate these worlds' potential for habitability and search for the presence of remotely detectable signs of life known as "biosignatures." we will discuss the strategies for exo-earth detection and characterization, including specific observational requirements for astrobiological assessments of exoplanetary environments with luvoir. the survey of the atmospheric composition of dozens of potentially habitable worlds would bring about a revolution in our understanding of planetary formation and evolution, and may usher in a new era of comparative astrobiology. | the search for exo-earths and biosignatures with the luvoir mission concept |
the hunt for ocean-covered, earth-sized exoplanets is rapidly gaining attention because of these planets' exciting potential and implications for habitability. understanding the atmospheres of these planets and determining the optimal strategy for characterizing them through transmission spectroscopy with our upcoming instrumentation is essential if we are ever to constrain the environments of these ocean worlds. for this study, we present simulated transmission spectra of tidally locked earth-like planets around m and k stars, utilizing gcm modeling results for ocean planets previously published by kopparapu et al. (2017) as inputs for our radiative transfer calculations performed using nasa's planetary spectrum generator (psg.gsfc.nasa.gov; villanueva et al. 2018). we identify trends in the expected transmission spectral signal of h2o features. in particular, we find that planets undergoing runaway water loss lack observable spectral features, while non-runaway planets share a consistent amplitude of their h2o features across a range of incident stellar fluxes. these trends allow us to calculate the exposure times necessary to detect water vapor in the atmospheres of ocean-worlds with the upcoming james webb space telescope (jwst) as well as several future flagship space telescope concepts under consideration (luvoir, habex and ost) for the brightest m- and k-type stars from the tess input catalog (tic). our calculations reveal that only a small subset of potentially detectable ocean planets in the habitable zones of cool stars may have realistic exposure times. we thus present a careful prioritization of targets that are most amenable to follow-up characterizations with next-generation instrumentation, in order to assist the community in efficiently utilizing precious telescope time. | synchronously rotating ocean earths around cool stars: what to expectra |
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 dynamics are subject to the interaction of many planetary features including: orbital dynamics, atmospheric composition, surface composition. exoplanet observing missions will observe but a small sampling from the full diversity possible, and given many parameters that cannot be directly observed, constraining potential targets for observability of habitable climatologies is as yet a wide open area for research. this study lays foundations for understanding the climatologies of land planets in particular. land is required not only to provide life a stable surface but also to support a stable carbonate-silicate cycle. modeling studies have also 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. 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, we fill 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 sample from the following ten variables: stellar temperature and spectra from observed stars, instellation, rotation period, obliquity, surface pressure, co2 content (in n2/co2 atmospheres), surface albedo, surface roughness, soil texture, and initial planetary water content. statistical analysis of the mean and distributions, spatial and temporal, of the ensemble climate states is used to uncover continuous relations between the variables and several metrics of habitability and their observability. from these we derive classifications of rocky land planet climatologies, offering a modeled uncertainty context in which observed planets might occur, and set foundations for further filling the parameter space with more diverse specifications of the planet size, and compositions of the surface and atmosphere. | diversity of habitable climatology of land exoplanets in a rocke-3d gcm perturbed parameter ensemble |
the university of rochester (ur) infrared detector group is working together with teledyne imaging sensors to develop megapixel hgcdte 15 𝜇𝑚 cutoff wavelength detector arrays for future space missions with the goal to identify key components of biosignatures in the atmospheres of exoplanets. this technology could have the capability of identifying the 15 𝜇𝑚 𝐶𝑂2 feature, seen in the three terrestrial planets orbiting in a habitable zone in our solar system. further investigations of the habitability of such rocky planets would then be determined by the detection of abundant oxygen (from the 9.6 𝜇𝑚 ozone feature) and water vapor in their spectra. to reach the 15 𝜇𝑚 cutoff goal, an intermediate step was taken by developing four ~13 𝜇𝑚 cutoff wavelength arrays to identify any unforeseen effects related to increasing the cutoff wavelength from the extensively characterized 10 𝜇𝑚 cutoff wavelength detector arrays developed for the neocam mission. the characterization of the ~13 𝜇𝑚 cutoff wavelength hgcdte arrays at ur allowed us to determine the key dark current mechanisms that limit the performance of these devices at different temperatures and bias when the cutoff wavelength is increased. we present dark current and well depth measurements of three arrays with a 15 𝜇𝑚 cutoff wavelength goal (actual cutoffs of 15.2, 15.5, and 16.7 𝜇𝑚 at a temperature of 30 k) and a summary of the ~13 𝜇𝑚 cutoff arrays. the goal of this project was to determine if hgcdte detector arrays are a better option than si:as detector arrays to cover this wavelength range since hgcdte devices give very high qe and require significantly less cooling. si:as devices require cooling down to ~6-8 k, while the best performing ~15 𝜇𝑚 hgcdte device showed a median dark current of 1.4 𝑒- /𝑠 (with applied reverse bias of 150 mv, or well depth of 49 𝑘𝑒- ) at a temperature of 23 k, while the best ~13 𝜇𝑚 device showed a median dark current of 0.2 𝑒- /𝑠 with the same applied bias and well depth of 44 𝑘𝑒- but at a temperature of 28 k (spitzer's focal plane equilibrated to ~28 k after cryogens were exhausted). although the ~15 𝜇𝑚 devices were developed for future space missions, the ~13 𝜇𝑚 devices may be used in ground based observatories, giving instruments access to the entire n-band while operating at temperatures attainable with closed cycle coolers, thereby eliminating the need for cryogens. | 15 micron cutoff hgcdte infrared detector arrays for exo-astronomy |
nasa's exoplanet exploration program (exep) guides the development of technology that enables the direct imaging and characterization of exo-earths in the habitable zone of their stars for future space observatories. here we present the coronagraph portion of the 2017 exep technology gap list, an annual update to exep's list of of technologies, to be advanced in the next 1-5 years. a coronagraph is an internal occulter that allows a space telescope to achieve exo-earth imaging contrast requirements (more than 10 billion) by blocking on-axis starlight while allowing the reflected light of off-axis exoplanets be detected. building and operating a space coronagraph capable of imaging an exo-earth will require new technologies beyond those of wfirst, the first high-contrast conronagraph in space. we review the current state-of-the-art performance of space coronagraphs and the performance level that must be achieved for a coronagraph.. | technologies required to image earth 2.0 with a space coronagraph |
we propose a high precision calibration scheme for a mid-ir exoplanet spectrometer. this new technology will enable high-precision transmission, emission, and phase curve spectroscopy for the characterization of exoplanets in and near the habitable zone, enabling the detection of biosignatures in rocky planets around the nearest m dwarfs. | the mid-infrared exo-planet climate explorer mirecle: exploring the nearest m-earths through ultra-stable mid-ir transit and phase-curve spectroscopy |
all life on earth requires liquid water, and hence the search for life beyond earth begins with the search for stable water on the surface or in the interior of a planet or moon. the habitable zone (hz) is traditionally defined as the region around a star in which the earth could retain surface water based on incident stellar radiation (instellation). a terrestrial-like planet, i.e. one without a significant hydrogen envelope, in the hz may support a surface water layer and may also support life. however, other effects can supersede the role of current incident flux and render a planet in the hz uninhabitable. examples include, but are not limited to, tidal heating into a runaway greenhouse, desiccation by early high-luminosity phases, and large-amplitude eccentricity cycles induced by companion planets. with the discovery of terrestrial planets in the hz of nearby stars, a revised and inclusive model of planetary habitability must be developed to provide robust interpretation of the history of habitable and inhabited exoplanets. we conclude with a brief description of a new computational tool, \texttt{\footnotesize{vplanet}, that provides a framework to couple the phenomena that affect the stability and longevity of liquid water in planetary environments. | after the habitable zone |
i will discuss recent work i have done to characterize trappist-1, a nearby exoplanet system hosting seven terrestrial-size planets, three of which are in the habitable zone. in the first part of this talk, i will report on my efforts to constrain the orbital properties of the smallest and farthest out planet in the system, trappist-1h, from k2 data de-trended with my systematics correction pipeline, everest. i will further discuss how the detection of trappist-1h with k2 confirmed the intricate resonant structure of the system, whose planets are all linked to their neighbors via three-body laplace resonances. this is the longest known chain in any exoplanet system and holds important clues for the formation and migration of the trappist-1 planets. in the second part of this talk, i will discuss ongoing work to characterize the trappist-1 system via planet-planet occultations (ppos), events during which one planet occults the disk of another, imparting a small photometric signal as its thermal or reflected light is blocked. because of the extreme coplanarity of the system, ppos should occur on average 1 - 2 times per day in trappist-1. i will discuss how the upcoming james webb space telescope (jwst) will likely be able to detect ppos in this system in the mid-infrared, and how these can be used to place exquisite constraints on the masses, eccentricities, and mutual inclinations of its planets. i will also show how photodynamical modeling of these events can eventually be used to reveal a planet's day/night temperature contrast, infer various atmospheric properties, and construct crude two-dimensional surface maps of alien worlds. | probing the trappist-1 system with k2, jwst, and beyond |
the kepler discoveries of terrestrial extrasolar planets candidates started the discussions of life conditions and possible conditions for habitable zone. unfortunately star winds and cosmic rays were almost omitted in consideration despite the fact that they are one of the main factors defining the space weather near earth. previously we made estimations of the star wind properties and star and galactic cosmic rays near proxima centauri and proxima b. the simple models, which were derived for the sun in 1950th-1960th, give the reasonable results for the star wind parameters and conditions on the orbit of proxima b. we generalize these models for different astrospheres including hot o-b and a stars to estimate the possible star wind fluxes, astrosphere parameters and cosmic rays' fluxes and fluences taking into account values of the magnetic fields, coronal temperatures etc. obtained results will be compared with earth's and archean earth's conditions. | cosmic rays and their interaction with astrospheres |
transit spectroscopy of terrestrial planets around nearby m dwarf stars is a primary goal of space missions in the coming decades. 3d climate modeling has shown that slowly rotating terrestrial extrasolar planets, at the inner edge of m dwarf habitable zones (hz), may possess significantly enhanced stratospheric water vapor compared to a rapidly rotating planet like earth. for host m-dwarfs with teff > 3000 k, synchronously rotating inner hz planets have been shown to retain moist greenhouse conditions (stratospheric water mixing ratio >10-3) despite low earth-like surface temperatures. this is promising for h2o detection in the atmospheres of habitable planets with the upcoming james webb space telescope (jwst). in such slow rotators, strong vertical mixing is expected to loft h2o high into the atmosphere. however, m dwarfs also possess strong uv activity, which may effectively photolyze stratospheric h2o. prior modeling efforts have not included the impact of high stellar uv activity on stratospheric h2o abundance. here, we employ a 1-d photochemical model with varied stellar uv, to assess whether h2o destruction driven by high stellar uv would affect the detectability of h2o in transmission spectroscopy. temperature and water vapor profiles are taken from published 3-d climate model simulations for an inner hz earth-sized planet around a 3300 k m dwarf with a pure n2-h2o atmosphere; they serve as self-consistent input profiles for the 1-d model. we find that as long as the atmosphere is well-mixed up to the 1 mbar pressure level, uv activity appears to not impact detectability of h2o in the transmission spectrum. the strongest h2o features occur in the jwst miri instrument wavelength range and are comparable to the estimated systematic noise floor of 50 ppm for a cloudless atmosphere. we also explore additional chemical complexity within the 1-d model by introducing other species into the atmosphere and discuss their impact on the transmission spectrum for both cloudy and cloudless cases. | impact of stellar uv activity on habitable moist terrestrial exoplanet atmospheres around m dwarfs |
the wfirst coronagraph instrument (cgi) will be the first coronagraph with wavefront control in space, with an expected instrumental raw contrast of 3*10^-9 at 150 milliarcseconds in the v band. the cgi will be capable of directly imaging and characterizing mature exoplanets in reflected light for the first time, with a prime focus on stars with known radial velocity (rv) planets. the majority of these rv planet hosting stars are at relatively far distances for coronagraphic imaging of their inner habitable zone. however, the recent discovery of four radial velocity planets around the near g-type star tau ceti (3.7 pc), including two potential super-earths located at the edges of its habitable zone, provides a great new opportunity for direct imaging with the wfirst/cgi. this underscores the importance of the continued search for radial velocity planets around nearby host stars, as it may reveal additional discoveries of planets in the habitable zone which then can be characterized by the wfirst/cgi. finally, the cgi may also detect habitable zone planets through blind searches around the very nearest stars (<5pc), and we also examine this potential here. | wfirst: discovery and characterization of planets in the habitable zone with the cgi |
in an attempt to select stars that can host planets with characteristics similar to our own, we selected seven solar-type stars known to host planets in the habitable zone and for which spectroscopic stellar parameters are available. for these stars we estimated ’empirical’ abundances of o, c, mg and si, which in turn we used to derive the iron and water mass fraction of the planet building blocks with the use of the model presented in santos et al. (2015). our results show that if rocky planets orbit these stars they might have significantly different compositions between themselves and different from that of our earth. however, for a meaningful comparison between the compositional properties of exoplanets in the habitable zone and our own planet, a far more sophisticated analysis (e.g. dorn et al., 2017) of a large number of systems with precise mass and radius of planets, and accurate chemical abundances of the host stars. the work presented here is merely the first humble step in this direction. | how alien can alien worlds be? |
we describe a possible roadmap to achieving the technological capability to search for biosignatures on an earth-like exoplanet from a future space telescope. the detection of earth-like exoplanets in the habitable zone of their stars, and their spectroscopic characterization in a search for biosignatures, requires starlight suppression that exceeds the current best ground-based performance by orders of magnitude. the required planet/star brightness ratio of order 1e-10 at visible wavelengths can be obtained by blocking stellar photons with an occulter, either externally (a starshade) or internally (a coronagraph) to the telescope system, and managing diffracted starlight, so as to directly image the exoplanet in reflected starlight. coronagraph instruments require advancement in telescope aperture (either monolithic or segmented), aperture obscurations (obscured by secondary mirror and its support struts), and wavefront error sensitivity (e.g. line-of-sight jitter, telescope vibration, polarization). the starshade, which has never been used in a science application, benefits a mission by being decoupled from the telescope, allowing a loosening of telescope stability requirements. in doing so, it transfers the difficult technology from the telescope system to a large deployable structure (tens of meters to greater than ~ 100 m in diameter) that must be positioned precisely at a distance of tens of thousands of kilometers from the telescope. two ongoing mission concept studies, habex and luvoir, include the direct imaging of earth-sized habitable exoplanets as a central science theme. | a possible technology development path to direct imaging of exo-earths from space |
here, we investigate the hypothesis that planetary magnetism has a significant effect on the maintenance of liquid water on an exoplanet by determining which of the currently detected planets have sufficient magnetosphere protection from cosmic and stellar irradiation. we used olsen & christiensen's model [1] to determine the maximum magnetic dipole moment of terrestrial exoplanets, further analyzing those located in the circumstellar habitable zone (chz). our results indicate that 70% of exoplanets currently defined as potentially habitable (rocky planets located in the chz), even with the best-case scenario of modelling the maximum possible dipole moment with the lowered magnetic protection threshold value, would not have a magnetic field strong enough to protect their surface, and consequently any potential water or life on it, against stellar and cosmic irradiation. | planetary magnetism as a parameter in exoplanet habitability |
the "missing methane problem" is one of the central mysteries in the exploration of exoplanetary atmospheres. whereas methane (ch4) is ubiquitous in the atmospheres of solar system giant planets, it has yet to be robustly detected in temperate exoplanetary atmospheres. molecules such as ch4 and ammonia (nh3) are expected to be prominent carriers of carbon and nitrogen in h2-rich atmospheres at temperatures below ~800 k. the presence or absence of ch4 in such atmospheres has major implications for our understanding of planet formation, atmospheric processes, and searches for chemical signatures in habitable-zone exoplanets. we propose a comprehensive jwst program to address this long-standing problem with high-precision transmission spectra over the 1-10 micron range for a homogeneous sample of four temperate mini-neptunes orbiting bright m dwarfs. these observations will be obtained using a combination of niriss, nirspec g395h and miri lrs instruments. the observations will provide unprecedented constraints on the atmospheric compositions of these targets, robustly resolving the missing methane problem and providing important insights into disequilibrium processes in the atmospheres. these observations will also allow us to a) constrain theories of planet formation and evolution of sub-neptune planets by determining their atmospheric metallicities and elemental ratios, b) build the first mass-metallicity (m-z) relation in the sub-neptune regime and c) test the extension of solar system m-z relation in c/h to lower masses. our program will pave the way for future searches of hydrocarbons and signatures of chemical disequilibrium in habitable-zone exoplanets. | a jwst search for missing methane |
observations were taken using the habitable-zone planet finder (hpf), a fiber-fed near-ir echelle spectrograph on the 10m hobby-eberly telescope (het). the hpf has a wavelength range coverage of 8079-12786å and resolving power of r~55000. (1 data file). | vizier online data catalog: 130 stellar and planetary parameters (bennett+, 2023) |
the plato 2.0 space mission (planetary transits and oscillation of stars) was selected by the esa science programme in february 2014, as the m3 mission to be launched in 2024. plato 2.0 will detect terrestrial exoplanets in the habitable zone of bright solar-type stars and characterise their bulk properties. the exoplanets will be detected by the weak eclipses they produce when transiting in front of their parent star, while the long uninterrupted observations will allow also to analyze the oscillations of these stars, yielding their internal structure and evolutionary state. the stellar sample targeted by plato is bright enough (v<11.5) to be able to confirm the planets candidates using radial velocity spectroscopy from ground, providing so a complete characterization of the exoplanetary systems. spain will contribute to the plato 2.0 instrument by providing the focal plane assemblies of its 34 telescopes, as well as the main electronics units which will perform onboard and in real time the photometric extraction of the stellar lightcurves. | the plato 2.0 mission. spanish contribution |
the robo-ao kepler planetary candidate survey is observing every kepler planet candidate host star (koi) with laser adaptive optics imaging to hunt for blended nearby stars which may be physically associated companions. with the unparalleled efficiency provided by the first fully robotic adaptive optics system, we perform the critical search for nearby stars (0.15" to 4.0" separation with contrasts up to 6 magnitudes) that pollute the observed planetary transit signal, contributing to inaccurate planetary characteristics or astrophysical false positives. we present approximately 3300 high resolution observations of kepler planetary hosts from 2012-2015, with ~500 observed nearby stars. we measure an overall nearby star probability rate of 16.2±0.8%. with this large dataset, we are uniquely able to explore broad correlations between multiple star systems and the properties of the planets which they host. we then use these clues for insight into the formation and evolution of these exotic systems. several kois of particular interest will be discussed, including possible quadruple star systems hosting planets and updated properties for possible rocky planets orbiting in the habitable zone. | the robo-ao koi survey: laser adaptive optics imaging of every kepler exoplanet candidate |
how common are habitable earth-like planets? this is a key question that drives much of current research in exoplanets. to date, we have discovered over one thousand exoplanets, mostly through the transit method. among these are earth-size planets, but these orbit very close to the star (semi-major axis approximately 0.01 astronomical units). potentially rocky planets have also been discovered in a star's habitable zone, but these have approximately twice the radius of the earth. these certainly do not qualify as earth "twins". several hundreds of multi-planet systems have also been discovered, but these are mostly ultra-compact systems with up to seven planets all with orbital distances less than that of mercury in our solar system. the detection of a planetary system that is the direct analog of our solar system still eludes us. after an overview of the current status of exoplanet discoveries i will discuss the prospects and challenges of finding such earth analogs from the ground and from future space missions like plato. after over two decades of searching, we may well be on the brink of finding other earths. | toward other earths |
we just discovered 3 short-period earth-sized planets transiting a nearby ultracool dwarf star. the inner two planets receive four and two times earth irradiation, placing them close to the inner edge of the habitable zone. with equilibrium temperatures between 250 - 400 k these planets likely present habitable regions, but the sustained activity of m dwarfs over hundreds of millions of years could impact their habitability. the system proximity (12 pc), its large planet-to-star radii ratios and high systemic velocity (-56 km/s) make it an amazing target to study the state and evolution of terrestrial planets atmospheres around a late m dwarf in the uv. yet large uncertainties in the strength of m dwarfs ly-alpha emission and hydrogen escape from small planets make it difficult to plan an efficient hst program to make such measurements. we thus propose a 4-orbit reconnaissance study to determine how hst unique uv capabilities can be optimally employed to observe this important exoplanet system in next cycles. here we will observe the star with stis at ly-alpha to 1) try and measure the stellar line, and 2) search for signatures of hydrogen escape from the planets, which would hint at evaporating water oceans. because several orbits remain possible for the third discovered planet, we will ensure the best scientific by focusing on the two inner ones. objective (1) will be achieved by observing the star twice, ensuring that the signal is high enough to constrain the intrinsic ly-alpha emission. objective (2) will be achieved by observing the transit of each of the two inner planets, allowing us to detect possible absorption of the stellar line caused by hydrogen exospheres | uv exploration of two earth-sized planets with temperate atmospheres |
for my dissertation under the supervision of dr. young, i investigate how stars of different mass and composition evolve, and how stellar evolution impacts the location of the habitable zone around a star. current research into habitability of exoplanets focuses mostly on the concept of the classical hz - the range of distances from a star over which liquid water could exist on a planet's surface - determined primarily by the host star's luminosity and spectral characteristics. with the ever-accelerating discovery of new exoplanets, it is imperative to develop a more complete understanding of what factors play a role in creating the “habitable” conditions of a planet. i discuss how stellar evolution is integral to how we define a hz, and how this work will apply to the search for habitable earth-like planets in the future.i developed a catalog of stellar evolution models for sun-like stars with variable compositions; masses range from 0.1-1.2 msol (spectral types m4-f4) at scaled metallicities of 0.1-1.5 zsol, and o/fe, c/fe, and mg/fe values of 0.44-2.28, 0.58-1.72, and 0.54-1.84, respectively. i use a spread in abundance values based on observations of variability in nearby stars. it is important to understand how specific elements (and not just total metallicity) can impact evolutionary lifetime. the time-dependent hz boundaries have also been calculated for each stellar track. additionally, i recently created a grid of models for m-dwarfs, and i am currently working to make preliminary estimates of stellar activity vs. age for each representative star in the catalog.my results indicate that to gauge the habitability potential of a given system, both the evolutionary history as well as the detailed chemical characterization of the host star must be considered. this work can be used to assess whether a planet discovered in the hz of its star has had sufficient time to develop a biosphere capable of producing detectable biosignatures. the catalog is designed for use by the astrobiology and exoplanet communities to characterize stars and their surrounding hzs for real planetary candidates of interest. | the diversity of chemical composition and the effects on stellar evolution and planetary habitability |
we present first results of the composition of laboratory-produced exoplanet haze analogues. with the planetary haze research (phazer) laboratory, we simulated nine exoplanet atmospheres of varying initial gas phase compositions representing increasing metallicities (100x, 1000x, and 10000x solar) and exposed them to three different temperature regimes (600, 400, and 300 k) with two different “instellation” sources (a plasma source and a uv lamp). the phazer exoplanet experiments simulate a temperature and atmospheric composition phase space relevant to the expected planetary yield of the transiting exoplanet survey satellite (tess) mission as well as recently discovered potentially habitable zone exoplanets in the trappist-1, lhs-1140, and proxima centauri systems. upon exposure to the energy sources, all of these experiments produced aerosol particles, which were collected in a dry nitrogen glove box and then analyzed with an ltq orbitrap xl™ hybrid ion trap-orbitrap mass spectrometer utilizing m/z ranging from 50 to 1000. the collected aerosol samples were found to contain complex organics. constraining the composition of these aerosols allows us to better understand the photochemical and dynamical processes ongoing in exoplanet atmospheres. moreover, these data can inform our telescope observations of exoplanets, which is of critical importance as we enter a new era of exoplanet atmosphere observation science with the upcoming launch of the james webb space telescope. the molecular makeup of these haze particles provides key information for understanding exoplanet atmospheric spectra, and constraining the structure and behavior of clouds, hazes, and other aerosols is at the forefront of exoplanet atmosphere science. | laboratory studies of planetary hazes: composition of cool exoplanet atmospheric aerosols with very high resolution mass spectrometry |
the search for earth-like exoplanets, orbiting in the habitable zone of stars other than our sun and showing biological activity, is one of the most exciting and challenging quests of the present time. nulling interferometry from space, in the thermal infrared, appears as a promising candidate technique for the task of directly observing extra-solar planets. it has been studied for about 10 years by esa and nasa in the framework of the darwin and tpf-i missions respectively [1]. nevertheless, nulling interferometry in the thermal infrared remains a technological challenge at several levels. among them, the development of the "modal filter" function is mandatory for the filtering of the wavefronts in adequacy with the objective of rejecting the central star flux to an efficiency of about 105. modal filtering [2] takes benefit of the capability of single-mode waveguides to transmit a single amplitude function, to eliminate virtually any perturbation of the interfering wavefronts, thus making very high rejection ratios possible. the modal filter may either be based on single-mode integrated optics (io) and/or fiber optics. in this paper, we focus on io, and more specifically on the progress of the on-going "integrated optics" activity of the european space agency. | integrated optics for nulling interferometry in the thermal infrared: progress and recent achievements |
we report on a unique detection methodology using the berkeley visible image tube (bvit) mounted on the 10m southern african large telescope (salt) to search for laser pulses originating in communications from advanced extraterrestrial (et) civilizations residing on nearby earth-like planets located within their habitability zones. the detection technique assumes that et communicates through high powered pulsed lasers with pulse durations on the order of 5 nanoseconds, the signals thereby being brighter than that of the host star within this very short period of time. our technique turns down the gain of the optically sensitive photon counting microchannel plate detector such that ~30 photons are required in a 5ns window to generate an imaged event. picking a priori targets with planets in the habitable zone substantially reduces the false alarm rate. interplanetary communication by optical masers was first postulated by schwartz and townes in 1961. under the assumption that et has access to a 10 m class telescope operated as a transmitter then we could detect lasers with a similar power to that of the livermore laboratory laser (~1.8mj per pulse), to a distance of ~ 1000 pc. in this talk we present the results of 2400 seconds of bvit observations on the salt of the star wolf 1061, which is known to harbor an earth-sized exoplanet located in the habitability zone. at this distance (4.3 pc), bvit on salt could detect a 48 joule per pulse laser, now commercially available as tabletop devices. | a new imaging technique for detecting interstellar communications |
this presentation will describe the highlights of the hz catalog and the plans for further validation of hz candidates and follow-up studies. | a catalog of kepler habitable zone exoplanet candidates |
the habitable exoplanet imaging mission (habex) is one of four flagship mission concepts currently under study for the upcoming 2020 decadal survey of astronomy and astrophysics. one of habex’s main goals will be a thorough study of planetary systems in our stellar neighborhood. this will include the characterization of any rocky planets in the habitable zones of these systems. rocky habitable zone planets are, by definition, worlds with the potential to host global liquid water surface oceans, and therefore the potential to harbor global biospheres. habex’s characterization of these worlds will include a search for signs of life on these planets. these signatures will be primarily spectroscopic in nature, and result from the suite of gases emitted by biota at the planet’s surface. in this poster, we will discuss habex’s abilities to detect potential biosiagnature gases, and the extent to which it can discrimninate biological sources of these gases from non-biological “false positives.” | habex and the search for biosignatures around nearby stars |
understanding how snowball episodes function on earth-like exoplanets is critical for planetary habitability. previous work has shown that glaciated planets in the habitable zone with low outgassing rates could be perpetually cycling through warm and snowball states. on earth, the neoproterozoic snowball events were followed by increases in the complexity of life and rises in atmospheric oxygen. gaps in thick, semi-global ice coverage (sea glaciers) could be maintained at the equator by ocean-ice-atmosphere dynamics. we investigate this idea by modifying a global ocean-thick-marine-ice model developed for modeling neoproterozoic snowball events to account for gaps in thick ice and interactions with atmospheric dynamics. asynchronous coupling of the marine-ice model and a 2d seasonal energy balance model will be used to simulate the climate of tidally-locked, glaciated exoplanets around m-stars. our hypothesis is that in the parameter regime that allows for sea glacier flow, ice flow will make gaps in the thick ice, and therefore an open ocean solution, less likely. this would suggest that oases in thick ice are a more viable survival mechanism for photosynthetic life during a snowball event. | investigating equatorial gaps in snowball earth sea glaciers on tidally-locked exoplanets around m-stars |
kepler, k2, and ground-based telescopes have detected around 3,750 exoplanets of which about 10 are temperate and rocky, making them potential candidates for further studies on habitability. an important gas that maintains habitability is nitrogen n2; it is one of the common building blocks of planetary atmosphere, and it is a greenhouse gas that maintains a planet's temperature above the freezing point of water. the main sink of nitrogen in the atmosphere is the production of no from lightning; furthermore, no drives synthesis of hno2, hno3, and hno4in the atmosphere. if bodies of liquid water (e.g. oceans) are present, these nitrogen-bearing species would be sequestered due to their high solubility and depleted from the atmosphere. therefore, it is important to study the efficiency of the conversion from n2to soluble nitrogen species which can represent a limit to the lifetime of nitrogen in the atmosphere. using epacris, an advanced atmospheric chemistry and radiative transfer code, we determine the lifetimes of n2in n2-co2atmospheres by varying the flux of no produced by lightning by three orders of magnitude based on earth's no flux. we study an earth-sized exoplanet with a 1-bar n2-dominated atmosphere, a co2mixing ratio of 5%, and in the habitable zone of an m dwarf star and a sun-like star. results for the m dwarf star's planet show a non-linear behavior of nitrogen lifetime when changing the no flux: it decreases non-linearly up to a minimum followed by a slow increase for an increasing no flux, with a minimum lifetime reached at the earth-like no flux. in other words, a higher lightning rate does not drive faster deposition of soluble nitrogen species. the minimum lifetime found in this study is >1 billion years, indicating that the n2in an n2-co2atmosphere on terrestrial exoplanets is kinetically stable over geologically long periods of time. | stability of nitrogen in exoplanetary atmospheres in contact with liquid water |
m dwarfs have much longer main sequence lifetimes than the sun and provide stable habitable zones for tens of billions of years, perhaps making m dwarf planets some of the most habitable in the galaxy. additionally, the smaller radii of m dwarfs allow us to more easily detect transiting earth-analog planets, due to the higher planet/star radius ratio of the system than of fgk stars. we seek to better understand the m dwarfs (known and new) in the kepler field, using the wealth of information provided by the kepler. we confirm a sample of m dwarfs using the crossmatch between the initial kepler dataset and the second gaia data release. we calculate the spectral energy distributions (seds) of these objects, using distances from gaia and available archival photometry (e.g., allwise, 2mass, sdss, and panstarrs). we use the seds to measure updated luminosities, temperatures, masses and radii using empirically based calculations for these stars, rejecting those that don't qualify as m dwarfs. using kepler light curves, we calculate rotation rates of these stars and compile, hα, uv, x ray and flare rate information from archival surveys. we show that white light (kepler bandpass, kp) flare strength is highly correlated with rotation rate for m dwarfs and that m dwarfs with fast rotation rates and higher flare strengths in the initial kepler dataset do not have any confirmed exoplanet detections. while the majority of the stars that we investigate have no confirmed exoplanet detections, a small part of this subsample are known to host transiting exoplanets. we measure updated planetary radii and equilibrium temperatures for these transiting exoplanets. comparing stellar populations with and without confirmed planets will allow us to examine how m dwarf magnetic strength and activity impact planetary occurrence. | fundamental and magnetic characteristics of m dwarfs in the kepler field |
stellar activity is currently a major limitation to the detection of very low mass planets around solar type stars using radial velocity techniques. various techniques have been implemented to mitigate this problem, without allowing to reach one mearth planets for stars similar to the sun yet. it is therefore crucial to estimate precisely the effect of activity on exoplanet detectability using realistic time series for various types of stars to overcome this problem. i will describe the basic processes at work and how we extended a realistic solar model to build representative time series of radial velocity, photometry, astrometry and chromospheric emission variability. we built coherent sets of stellar parameters covering a large range in effective temperature (k4-f6) and average activity levels. such simulations are extremely useful to better understand the relationship between rv, astrometry and activity indicators and the limitations of correction techniques. i will present the impact of activity on the detectability of earth mass planet in the habitable zones of those stars using radial velocity and high precision astrometry and discuss their respective performance. | search for earth analogues in the habitable zone around solar type stars: radial velocity or astrometry? |
the habex and luvoir concepts aim to directly image and spectrally characterize potentially habitable exoplanets. using exosims, realistic mission observing constraints, and dynamically responsive scheduling, we simulate the exoplanet detection and characterizations over monte carlo realizations of synthetic planets around nearby stars. we use identical astrophysical inputs and the observing scenarios of each concept to evaluate a common comparison of the detection and spectral characterization yields of habex and luvoir. habex is evaluated for the 4m hybrid starshade and coronagraph architecture, the 4m coronagraph only architecture, and the 3.2 m starshade only architecture. luvoir is evaluated for the 15 m architecture a presented in their interim report. the scenarios are scheduled to respond dynamically to the number of detections/no-detections of a target and success of characterization as well as the optimal slews for the starshade. yield analysis shows that both concepts can directly image and spectrally characterize earth-like planets in the habitable zone and that each concept has complementary strengths. © california institute of technology 2018. all rights reserved. government sponsorship acknowledged. | standard evaluation of exoplanet yield for the luvoir and habex concept studies |
one of the core goals of the kepler mission was to determine the frequency of earth-like planets that orbit sun-like stars. accurately estimating this planet occurrence rate requires both a well-vetted list of planets and a clear understanding of the stellar target search sample. previous ground-based follow-up observations have, through a variety of methods, sought to better our knowledge of those stars that are known to host planets. kepler stars without detected planets, however, have as of yet not been examined as closely with respect to exoplanet occurrence. in this presentation, we better constrain stellar multiplicity for stars around which kepler could have theoretically detected a transiting earth-sized planet in the habitable zone. we subsequently aim to improve estimates of etaearth — the frequency of potentially habitable, earth-sized planets — with our data. with adaptive optics observations of 71 stars from the shane 3-m telescope at lick observatory, we report 14 stellar companions within 4″ of 13 kepler target stars. of these companions, we determine through multiple independent methods that 7 stellar companions are likely to be bound to their primary. we then extrapolate the results of this study to adjust the input stellar sample to kepler's publicly available dr25 products, flagging and removing stars on a probabilistic basis as determined by our observed multiplicity rate. in doing so, we find that the occurrence rate of potentially earth-like planets orbiting gk stars is roughly 14% higher than previously calculated. in addition to informing occurrence estimates, the multiplicity results from this study can be used in further investigations into the architectures of planetary systems orbiting stars with stellar companions. | a closer look at planet occurrence rates: ao follow-up of 71 stars in the kepler field |
terrestrial extrasolar planets around cool host stars are prime targets in the search for habitable surface conditions and biosignatures with current and near-future instruments like the james webb space telescope (jwst). we investigate the potential atmosphere of earth-like planets around cool host stars and calculate whether atmospheric features would be detectable in the near future. we find that the abundance of water and methane increases in such atmospheres. due to the more pronounced atmospheric absorption and higher signal to noise ratios for earth-like planets around cool stars, the detectability of the atmosphere is increased compared to an earth around the sun at the same distance. we conclude that the jwst could provide enough precision to be able to partly characterise the atmospheric composition of earth-like planets around cool host stars. | detectability of atmospheric features of earth-like planets in the habitable zone around cool host stars |
the large ultra violet-optical-infrared (luvoir) surveyor is one of four mission concepts being studied by nasa in preparation for the 2020 astrophysics decadal survey. luvoir is a general-purpose space-based observatory with a large aperture of 8 m (luvoir-b) or 15 m (luvoir-a) and a total bandpass spanning from the far-uv to the near-infrared. one of luvoir's main science objectives is to directly image temperate earth-sized planets in the habitable zones of sunlike stars, measure their spectra, analyze the chemistry of their atmospheres, and obtain information about their surfaces. measuring the frequency of habitable conditions in nearby systems requires observations of dozens of candidate exoplanets, and luvoir anticipates observing 28 (luvoir-b) or 54 (luvoir-a) exo-earth candidates. these large sample sizes maximize our chances of finding other habitable worlds, and in the absence of water vapor detections, they would allow us to place an upper limit on the frequency oceans occur on rocky worlds within their habitable zones: less than 10% (luvoir-b) or 5% (luvoir-a). on the other hand, if earth-like conditions are common, a stunning vista of hospitable new worlds will be unveiled. luvoir will not only complete the census of nearby exo-earths but will probe the atmospheres of these planets for biosignature gases. luvoir will search for key biosignature gases such as o2, ch4, and o3, and it will use measured information to put those gases into their full planetary contexts to rule out biosignature false positives. additionally, the luvoir team has used earth's full inhabited history to guide our search strategy, and luvoir would be capable of detecting the diverse biosignatures of earth through time for as long as our planet has supported life. we will discuss the strategies for exo-earth detection and characterization, including specific observational requirements for astrobiological assessments of exoplanetary environments with luvoir. the survey of the atmospheric composition of dozens of potentially habitable worlds would bring about a revolution in our understanding of planetary formation and evolution, and may usher in a new era of comparative astrobiology. | the search for biosignatures and exo-earths with the luvoir mission concept |
a universal aspect of exoplanet science is that the information available is very limited, and the sample of planets we can study in situ is very small. detailed, informative observations of exoplanets are observationally resource-intensive and technically difficult, and a growing body of numerical simulations of planet formation, evolution, and climate shows that inference from these limited observations is fraught with numerous observational and physical degeneracies. at a time when the number of observational targets is large but the resources available to study them are limited, we need low-cost techniques which nonetheless permit robust classification. critically, these techniques must be developed in advance to prevent wasted resources. the particular challenge of classifying rocky exoplanet climates in the habitable zones of sun-like stars has in the past been frustrated by many potential degeneracies, particularly the possibility of widespread clouds. using hundreds of full 3d climate models, each with detailed simulated reflectance spectra, we present a new technique to uniquely identify cold, ice-covered 'snowball' planets through broadband visible and infrared photometric colors. the occurrence rate of snowball planets in the habitable zone is sensitive to planets' geophysical properties, so this low-cost technique for identifying snowball planets in observed populations represents a possibly unique way to test geophysical theories of planet formation and evolution. while in our models serious degeneracies prevent the ultimate goal of easy and robust identification of temperate, earth-like climates, this technique could permit pre-screening of potential follow-up targets. we identify several useful observing bands that will be accessible to planned instruments on upcoming large ground-based telescopes, and which may guide future instrument design. our work shows low-snr broadband photometry can distinguish between different climates on earth-like planets, which permits informative survey science and potentially provides a roadmap for improving other exoplanet inference problems. | low-cost inference of terrestrial climates with broadband photometry |
we propose xmm-newton/epic observations of 14 recently discovered nearbyexoplanet hosts. together, they host a combined 7 earth-like planets and36 known planets overall. many of the planets are located in or near thepresumed habitable zones of their host stars. the targets cover stellartypes from f to m. while a star's photometric luminosity is important,the high energy uv/x-ray irradiation from the corona is a major driverof photochemistry, upper atmospheric heating, and atmospheric mass lossin exoplanets. we will obtain a snapshot of the current temperaturesand fluxes using epic-pn/mos. these data will start the process ofunderstanding the possible paths of atmospheric evolution. | x-rays in the prime of life: high energy dose to exo-earths |
the titius-bode (tb) relation’s successful prediction of the period of uranus was the main motivation that led to the search for another planet between mars and jupiter. this search led to the discovery of the asteroid ceres and the rest of the asteroid belt. the tb relation can also provide useful hints about the periods of as-yet-undetected planets around other stars. in bovaird & lineweaver (2013) [1], we used a generalized tb relation to analyze 68 multi-planet systems with four or more detected exoplanets. we found that the majority of exoplanet systems in our sample adhered to the tb relation to a greater extent than the solar system does. thus, the tb relation can make useful predictions about the existence of as-yet-undetected planets in kepler multi-planet systems. these predictions are one way to correct for the main obstacle preventing us from estimating the number of earth-like planets in the universe. that obstacle is the incomplete sampling of planets of earth-mass and smaller [2-5]. in [6], we use a generalized titius-bode relation to predict the periods of 228 additional planets in 151 of these kepler multiples. these titius-bode-based predictions suggest that there are, on average, 2±1 planets in the habitable zone of each star. we also estimate the inclination of the invariable plane for each system and prioritize our planet predictions by their geometric probability to transit. we highlight a short list of 77 predicted planets in 40 systems with a high geometric probability to transit, resulting in an expected detection rate of ~15 per cent, ~3 times higher than the detection rate of our previous titius-bode-based predictions.references: [1] bovaird, t. & lineweaver, c.h (2013) mnras, 435, 1126-1138. [2] dong s. & zhu z. (2013) apj, 778, 53 [3] fressin f. et al. (2013) apj, 766, 81 [4] petigura e. a. et al. (2013) pnas, 110, 19273 [5] silburt a. et al. (2014), apj (arxiv:1406.6048v2) [6] bovaird, t., lineweaver, c.h. & jacobsen, s.k. (2015, in press) mnras, arxiv:14126230v3. | using a generalized version of the titius-bode relation to extrapolate the patterns seen in kepler multi-exoplanet systems, and estimate the average number of planets in circumstellar habitable zones |
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