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extensive interest in exoplanet research is motivated in part by the search for evidence of life on a subset of these worlds. this scientific search relies on measurements of star spectra, and upon the planet spectra, photometry, and mass. the ability to measure these planet properties at the required sensitivity has been the focus of sustained technology investments by nasa for the past decade, investments which are now achieving milestones and sensitivity thresholds that for the first time enable mission concepts capable of a search for evidence of life on exoplanets. most notably, broadband contrast levels for coronagraphs and starshades have recently been demonstrated to meet better than 4×10-10 and 10-11, respectively — thresholds required for spectral characterization of exo-earths in the habitable zones of sun-like stars. nasa's exoplanet exploration program (exep) identifies technology gaps pertaining to possible exoplanet missions and works with the community to identify and track technologies to prioritize for investment, and ultimately to close the gaps. the decadal survey testbed, a nasa exep facility for testing next-generation coronagraphs, has recently demonstrated contrast performance at better than 4×10-10. a sub-scale starshade validation demonstration has met the 10% broadband visible contrast threshold of better than 10-10 contrast. a technology readiness level 5 milestone was recently met with a laboratory demonstration of a novel formation flying sensor that demonstrates the required lateral position sensitivity. this poster describes the recent technology breakthroughs and the enabling impact on mission concept studies being submitted to the 2020 astro decadal survey for direct imaging of exoplanets and spectral characterization to search for evidence of life. | progress on starlight suppression technologies for nasa direct imaging missions |
the recent discovery of exoplanets with putative habitable zones which may be as frequent as 1025 stimulate the interest in the origin of life on the exoplanets but also on the earl earth (ee). meteorites and missions to mars or moon teach us about their composition, and make us think about the origin of life in general. prebiotic molecules such as amino acids, nucleosides, and fullerenes arrived from extraterrestric space and cyanobacteria and archaea are inhabitants of the ee. they exhibit properties such as protein synthesis, which requires advanced machineries adapted to our earth. what could be early precursors of such mechanisms. what kind of life can we envision in its simplest form? molecules which can replicate, mutate, and evolve are signatures of life.the simplest such biomolecules on earth may be non-protein-coding (nc)rna catalytic rna, the ribozymes and viroids, which can fulfill many protein functions, including replication, evolution, and are a prerequisite for peptide synthesis. ribozymes/viroids can evolve to higher complexity. archaea and bacteria resemble giant viruses suggesting a continuous transition from dead to living matter. archaea are extremophiles which revolutionalized our view on what life can be like in respect to environmental conditions and specialized metabolic pathways. some exotic spots on earth can teach us about other habitable zones. meteorites help to understand chemical compositions on other planets and the consequences for life. during evolution loss and gain of of genetic information are important evolutionary driving forces. viroids are discussed as models for potentially other forms of life. simulators of mars environment are under study to determine possible effects on biological sepcimens.ref: broecker and moelling geosciences (2019), annals ny acad sci. (2019), frontiers microbiol (2019). book: moelling:viruses more friends than foes world scientific press ( 2017) | forms of life on early earth as model for exoplanets? |
for providing the maximal carrying capacity and expansive potential of a planetary system (ps), optimal utilization of the orbital material is required. it raises the question of suitability of various objects in a planetary system for the purpose of terraforming and developing full-scale open biospheres.the term "biosphere substrate" (bs) is introduced for celestial bodies, like terrestrial planets or big gas giant moons, suitable to sustain a full-scale open biosphere after terraforming. the purpose of the work is to examine the range of parameters for a biosphere substrate.most importantly, to be a bs, a celestial body gravity should sustain a full-scale open breathable atmosphere dense enough after terraforming in astrophysical time scale comparable to the lifecycle of a planetary system. extremely high gravity is also the limit for complex life forms. the gravity is the main parameter that is the most difficult to be influenced, thus the range of object sizes fitting the bs definition is examined.the capability of a celestial body to retain breathable atmosphere during a time interval comparable to the planetary system life cycle depends on its magnetic field strength. the lower boundary of the objects sizes fitting the bs definition is studied on the basis of their capability to hold hot convecting interiors for strong enough magnetic fields during a ps life cycle.as the chemical composition of a bs's surface, hydrosphere and atmosphere can be drastically adjusted in most cases by importing asteroid and cometary material, this factor in most cases does not determine whether a celestial body can become a bs. but for water worlds where any solid material to build biological bodies and industrial structures can be more than thousand kilometers deep, chemical composition can become an issue, while this problem can be solved to some extent by importing solid materials (asteroids). also, concentrations of some chemical elements and compounds in extremely toxic quantities in crust might be an obstacle to develop a full-scale open biosphere. thus, the range of chemical compositions for celestial bodies of suitable sizes is also reviewed.the temperature is another important parameter, as a molten celestial body cannot become a bs in near term, but can become a bs when it cools enough. the temperature factor and capabilities to adjust it are also estimated.for a full-scale open biosphere development, there must be a source of energy. a bs orbit can go inside the circumstellar habitable zone, or can be partially inside and partially outside it for highly elliptical orbits. possibilities to extend a circumstellar habitable zone with large orbital light diffusers and light concentrators are researched.for planets with solid crusts, their rotation can be adjusted by hitting asteroids and comets strictly tangentially with high velocities to gain required spin. but for water worlds and tidally locked satellites, rotation can be an issue. the rotation factor is also examined.the work attempts to introduce a new concept and the term that can be used for further terraforming research, developing a mathematical model of its limits. our estimations are required to be discussed with a wide range of relevant specialists in the linked fields of studies, such as astrophysics, especially exoplanets characterization professionals; astrochemistry; astrobiology; planetary science, etc. to provide the basis for this discussion, the article suggests preliminary estimations of the parameters crucial for selection of bs candidates. | biosphere substrate and its parameters range |
the kepler and k2 missions have provided the astronomical community with unprecedented amounts of data to search for transiting exoplanets and other astrophysical phenomena. here, we present a low-mass binary system hosting a small transiting planet observed in k2 campaign 4. the candidate was identified by citizen scientists using the exoplanet explorers project hosted on the zooniverse. follow-up observations and subsequent analyses validate the planet and indicate that it likely orbits the lower-mass companion star on a 31.34 day period. this orbit places it near the habitable zone of its host star. the planet resides in a system with a unique architecture and further follow-up may provide insight into its formation and evolution. additionally, its estimated size straddles the observed gap in the planet radius distribution. planets of this size occur less frequently and may be in a transient phase of radius evolution. this planet is the third identified by citizen scientists using exoplanet explorers and its discovery exemplifies the value of citizen science in the era of kepler, k2, and tess. | a small transiting planet discovered by citizen scientists |
the wide field infrared survey telescope (wfirst), now in phase b development, is nasa's next large space observatory, scheduled for launch in 2025. it contains two primary science instruments: a wide field instrument (wfi) to carry out surveys of galaxies in the near infrared; explore the properties of dark energy and dark matter; and carry out a microlensing survey to complete the census of exoplanets, and a coronagraph instrument (cgi) to demonstrate high-contrast technology for exoplanet imaging and spectroscopy. understanding how to implement the technology for cgi is a critical step toward future, larger missions targeted at direct imaging of earthlike planets in the habitable zone of nearby stars. if successful, cgi will also carry out a participating science program targeted at large jupiter size planets and disks. this talk will present an overview of the instrument, its key enabling technologies, and its operational plans, including its science program. also presented will be the phase b status of the instrument and plans moving forward. | the wfirst coronagraph instrument (cgi): an update |
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 60 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 probe mission concept study for the precise radial velocity detection of earth-mass exoplanets |
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 (8-15 m) 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 sun-like stars, measure their spectra, analyze the chemistry of their atmospheres, and obtain information about their surfaces. luvoir can also observing potentially habitable exoplanets transiting nearby m dwarf stars. such observations will allow us to evaluate these worlds' 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 biosignatures and exo-earths with the luvoir mission concept |
future space missions such as origins space telescope (ost) will be the instrument of choice to detect these bio-signatures in exoplanets around m-dwarfs by means of mid_ir transit spectroscopy. however, current mid-ir detectors have significant problems with stability. as a result, those detectors are not expected to provide the required stability of ~5 ppm needed for a reliable detection of the spectral lines from the most important atmospheric tracers for biological activiaty on the planet. here we describe the science enabled, as well as the development of an ultra-stable mid-ir array spectrometer demonstration for exoplanet transits, which includes a calibration system that, as we show, is needed to achieve the required sensitivity for the detection of atmospheric bio-signatures in habitable-zone planets around m-dwarfs. the spectrometer will be demonstrated with arrays of transition edge sensor detectors (tes). these devices are known to be intrinsically very stable and the required detector parameters (sensitivity, dynamic range) for space based mid-ir transit spectroscopy can be easily met with existing devices. no new detector developments are required. this project will include the development of a high-accuracy calibration system with a stable reference source. this scheme will allow for real time monitoring of the detector gain, which we anticipate will result in a background limited performance with the required stability of better than 5 ppm for the detection of bio-signatures in a designated spectrometer flying e.g. on the ost space tele-scope, and as such will help to answer one of nasa's main questions: "are we alone?" | an ultra-stable mid-infrared detector for the detection of bio-signatures by means of exo-planet transit spectroscopy |
the large uv/optical/infrared surveyor (luvoir) is a concept for a powerful general-purpose observatory spanning the far-uv to the near-infrared. a major goal for luvoir is characterizing a wide range of exoplanets with direct images and spectra, including rocky earth-sized planets in the habitable zones of solar-type stars. these data will allow a diverse set of investigations, including analysis of terrestrial planet atmospheres, explorations of planet surfaces, discovery of potentially habitable exoplanets, and searches for evidence of global biospheres. a key objective is to conduct these studies on a set of candidate habitable exoplanets large enough to constrain the frequency of habitable conditions (dozens of rocky planets orbiting solar-type stars). luvoir would simultaneously enable a great leap forward in a broad range of astrophysics — from the epoch of reionization, through galaxy formation and evolution, to star and planet formation. powerful remote sensing observations of solar system bodies will also be possible. here we provide a high-level overview of the luvoir mission science goals and current observatory architectures. two variants are being designed in preparation for the astro2020 decadal survey. luvoir-a features a 15-m diameter on-axis primary mirror and luvoir-b has an 8-m off-axis primary mirror. four candidate instruments are being studied: 1) a nuv to nir high-performance coronagraph (eclips), 2) a wide-field nuv to nir imaging camera (hdi), 3) a fuv to optical multi-resolution, multi-object spectrograph (lumos), and 4) a high-resolution uv spectropolarimeter (pollux). finally, perhaps luvoir's most important scientific capability is its ability to address the science questions of the 2040s and beyond that astronomers have not yet thought to ask. | telling the story of life in the cosmos: overview of the luvoir space observatory concepts |
studying extreme climate patterns on earth-like planets as a function of atmospheric greenhouse gases, planetary obliquity, orbital eccentricity, solar irradiance variations and location within the host star's habitable zone is needed to determine whether such planets are habitable for life as we know it. studying the behavior of climate on hypothetical earth-like planets also provides insight into the future climate of our own planet. a database of climate models based on different orbital parameters, solar irradiance and atmospheric composition will provide a valuable resource to the astrobiology community in support of future detections of exoplanets with masses, sizes, and compositions similar to earth. due to its user-friendly interface to a research grade 3-d climate model code, the educational global climate model (edgcm) was selected to perform a limited number of simulated models using the land configuration of earth, but with varying amounts of greenhouse gases, orbital parameters, and axial tilts. it is found that the edgcm is capable of simulating 3-d climate models for hypothetical earth-like planets for a limited number of cases, with several important restrictions on the initial conditions. | an investigation of 3-d climate patterns on hypothetical earth-like planets |
mercury's interaction with the solar wind is unique in our solar system due to its weak global magnetic field and the planet's proximity to the sun. the magnetosphere of mercury is therefore highly dynamic, especially during times of coronal mass ejections (cmes), which travel at high speeds compared to the solar wind and carry mass and magnetic field from the sun. it has been long hypothesized and modeled, but never observed, that the magnetic flux on mercury's dayside may be completely eroded or compressed below the surface during extreme conditions. such an event allows mercury to temporarily act as an unmagnetized airless body, with the cme plasma interacting directly with mercury's surface, weathering the regolith and sputtering particles into the exosphere. here, using messenger data, we present the first observations of a cme compressing mercury's dayside magnetosphere below the surface, accompanied by a ∼40% increase in the peak magnetospheric field and a ∼300% increase in the magnetotail field. these phenomena have not been observed at any planet until now. bepicolombo, arriving at mercury during the next solar maximum, will be well positioned to observe such magnetospheric collapse events in more detail, and we make predictions for these observations of the magnetosphere/cme interaction. the collapse of mercury's dayside magnetosphere has important implications for exoplanets in the so-called "habitable zone" of magnetically active m dwarf stars, as such events are likely to be much more common in these systems. loss of planetary magnetospheres could significantly contribute to planetary atmospheric loss, affecting habitability and the potential for emergence of life. | on the collapse of mercury's dayside magnetosphere |
an integrated database of confirmed exoplanets has been developed and launched as “exokyoto,” for the purpose of better comprehension of exoplanetary systems in different star systems. the hoststar module of the database includes not only host stars for confirmed exoplanets, but also hundreds of thousands of stars existing in the star database listed in (hyg database). each hoststar can be referred to in the catalogue with its habitable zone calculated, based on the observed/estimated star parameters. for outreach and observation support purpose, exokyoto possesses stellar windows, developed by the xlib & ggd module, and interfaces with googlesky for easy comprehension of those celestial bodies on a stellar map. target stars can be identified and listed by using this database, based on the target magnitude, transit frequency, and photon decrease ratio by its transit.if we interpolate deficient data using assumed functions about the exoplanets that were discovered until now, sub-neptune size (1.9-3.1r_earth) are the most common (971); then super earth size (1.2-1.9 r_earth) have been allocated (681).using the solar equivalent astronomical unit (seau), most of the exoplanets discovered are within a venus equivalent orbit (3029), and 197 are located within the habitable zone (venus to mars equivalent orbit). if we classify them using kopparapu et al.(2013), within recent venus equivalent orbit (3048), there are 130 located in the habitable zone (runaway greenhouse-maximum greenhouse). for example, kepler-560b is defined as in the habitable zone by its seau, but not by kopparapu et al. (2013). furthermore, based on an exoplanet's solar revolution, radius, assumed mass (larsen & geoffrey, 2014), transit parameters , and main start information (location, class, spectral class, etc.); observation target selection is practical and possible.in addition to the previous habitable zone based on the normal radiation flux from the host star, we'll discuss stellar flares activities which may disturb planets located in the habitable zone through high energetic particles.*those numbers are in february 2017 | development of exoplanet database "exokyoto" aiming for inter-comparison with different criteria of habitable zones |
exploration and searching for life in other stellar systems have shown that its development and sustainability depend of very specific environment conditions. due to that, preservation of the equilibrium of this conditions in our planet is very important, because small changes on it can generate high repercussions in its habitability. this work shows some preliminary results from an environmental monitoring network (racimo, red ambiental ciudadana de monitoreo) conformed by automatic meteorologic stations located on seven high-schools at metropolitan zone of bucaramanga, colombia. data recorded by monitoring network are stored in an open web repository which can be accessed by citizens from any place with internet connection. these stations called uvas, were developed under creative commons license, that is to say, software, hardware and data free, besides these can be built by students due to its flexibility. the uvas are modular and re-programmable, that is, any sensor can be added to the stations and then re-configure its firmware remotely. besides, uvas work in automatic way, after the first setup, they will be self-sufficient and won't depend of human intervention. the data, of each uva, are recorded with a temporal synchrony and then are upload at central repository by means of wifi, ethernet or gsm connection. the stations can be power supplied by a solar system or the electrical grid. currently, uva record variables such as: pressure, temperature, humidity, irradiance, iluminance, ambient noise, rain, cloudiness, co2 and no2 concentration, lighting, seismic movements and its geographic position. on other hand, a calibration system has been developed to validate the data recorded by racimo. this project, started from an astroclimate an exoplanets habitability conditions, became an independent citizen science project to rise awareness about the very particular conditions enjoyed in our earth planet. | astroclimate, a citizen science climate awareness |
we used california planet search ca ii h and k core emission measurements to identify and characterize chromospheric activity cycles in a sample of main-sequence fgk stars. about a dozen of these with existing rosat archival data were targeted with swift to obtain a current epoch x-ray flux. we find that coronal variability by a factor of several is common on decade-long timescales (we attempt to link to the chromospheric cycle phase) but can also occur on short timescales between swift visits to a given target, presumably related to stellar rotation and coronal inhomogeneity or to small flares. additionally, we present new swift monitoring observations of two m dwarfs with known exoplanets: gj 15a and gj 674. gj 15a b is around 5.3 earth masses with an 11.4 day orbital period, while gj 674 is around 11.1 earth masses with a 4.7 day orbital period. gj 15a was observed several times in late 2014 and then monitored at approximately weekly intervals for several months in early 2016, for a total exposure of 18 ks. gj 674 was monitored at approximately weekly intervals for most of 2016, for a total exposure of 40 ks. we provide light curves and hardness ratios for both sources, and also compare to earlier archival x-ray data. both sources show significant x-ray variability, including between consecutive observations. we quantify the energy distribution for coronal flaring, and compare to optical results for m dwarfs from kepler. finally, we discuss the implications of m dwarf coronal activity for exoplanets orbiting within the nominal habitable zone. | swift x-ray monitoring of stellar coronal variability |
it is well known that rocky planets located closer to their host stars than the inner boundary of the habitable zone are likely expiencing hot climate and could lose their oceans. generally it is assumed that the main bottleneck controlling the timescale of water loss on these planets are the loss of hydrogen and oxygen from the top of the atmospheres because climate control is already overcome. in this work we study the photolysis of water vapor in the middle atmospheres of such planets using observed stellar uv spectra. the results reveal that water loss from such planets could be limited by uv photons in some cases. thus some exoplanets with hot climate may enjoy their oceans with extended period of time than previously predicted. | impact of photolysis on the loss of water vapor from rocky exoplanets |
satellite observations and radiative calculations show that earth's outgoing longwave radiation (olr) is an essentially linear function of surface temperature over a wide range of temperatures (>60 k). although the evidence for a linear relation was first pointed out more than 50 years ago, it is still unclear why this relation is valid. linearity implies that earth's olr does not follow the non-linearity suggested by the stefan-boltzmann law, σts4, and has important consequences for past and future climate change: if olr is approximately linear, then earth's longwave climate feedback, dolr/dts, is approximately constant, such that radiative forcing has the same impact in warm as in cold climates. here we present a simple semi-analytical model that explains earth's linear olr as an emergent property of an atmosphere whose greenhouse effect is dominated by a condensible gas. we show that linearity arises from a competition between the surface's increasing thermal emission and the narrowing of spectral window regions with warming, and breaks down at high temperatures once continuum absorption cuts off spectral windows. our model provides a new way of understanding the longwave contribution to changes in earth's climate sensitivity. moreover, our model predicts that atmospheres dominated by exotic condensible greenhouse gases also develop a near-linear olr, such as hot rocky exoplanets covered with lava oceans and with silicate-oxide vapor atmospheres or cold super-earths beyond the outer edge of the habitable zone with thick co2 oceans and atmospheres. future space telescopes could thus study these exotic worlds as analogs of our own h2o-dominated climate. | the emergent linearity of outgoing longwave radiation in a moist atmosphere: implications for the climates of earth and extrasolar planets. |
in this poster, we use an empirical solar model developed by schrijver, derosa, et al. to simulate the expected large-scale coronal field and stellar activity of m-dwarf stars such as proxima centauri, with the aim of providing relevant stellar input into studies of star-planet interactions in exoplanet systems. following schrijver et al. (2001), we perform a control simulation using typical input parameters for the solar case in order to demonstrate the robustness of the model in representing magnetic flux transport on the sun's surface. we then present simulations conducted using input parameters matching the best-known estimates of the stellar magnetic field of proxima centauri. this series of proxima centauri-based simulations will represent the effects on stellar surface flux emergence and dispersal due to variations in initial conditions such as mean stellar magnetic field strength and flux emergence rates. such studies may open further avenues of research into stellar magnetic activity of exoplanet host stars and the effects of such activity on exoplanet habitability. | large-scale magnetic field simulations for proxima centauri: a test case for active m-dwarf stars with habitable zone planets |
a plethora of nearby, terrestrial exoplanets has been discovered recently by ground-based surveys. excitingly, some of these are in the habitable zones of their host stars, and may be hospitable for life. however, all the planets orbit small, cool stars and have considerably different irradiation environments from the earth, making them vulnerable to atmospheric escape, erosion and collapse. atmosphere characterization is therefore critical to assessing the planets' habitability. i will discuss possible jwst thermal emission measurements to determine the atmospheric properties of nearby terrestrial planets. i will focus on prospects for detecting physically motivated atmospheres for planets orbiting lhs 1140, gj 1132, and trappist-1. i will also discuss the potential for using phase curve observations to determine whether an atmosphere has survived on the non-transiting planet proxima b. | prospects for detecting thermal emission from terrestrial exoplanets with jwst |
the kepler mission’s latest catalog of planet candidates (data release 25 koi catalog at the nasa exoplanet archive) was released in june of 2017. the catalog contains 4034 candidates including a significant population of terrestrial-size planets in the habitable zone of fgk dwarf stars. i will highlight what we know about these planet candidates in the dr25 catalog and discuss some of the caveats when working with these detections. specifically, i will discuss how the noise in the kepler light curves (from both the instrument and the stars) is known to occasionally produce weak, transit-like signals. we use simulations of this noise to measure how often these signals sneak into the catalog. i will also demonstrate ways to select a high-reliability sample using information available in the catalog. such considerations may prove useful for anyone planning to use these planet candidates for occurrence rate calculations, choosing targets for follow-up, or deciding which planet to visit on his/her next holiday. | kepler’s dr25 most earth-like planet candidates: what to know before you go |
the simultaneous detection of carbon dioxide (co2) and abundant methane (ch4) in the atmospheres of habitable exoplanets is a promising biosignature combination [1]. the absence of carbon monoxide (co) would strengthen biogenicity because many non-biological scernaios that generate co2 and ch4 would also be expected to produce co, and because co is readily consumed by microbes. this co2+ch4-co biosignature combination is arguably more common than oxygen/ozone biosignatures because of the relative simplicity of methanogenesis in comparison to oxygenic photosynthesis. moreover, it has been shown that the co2+ch4-co biosignature combination is more easily detectable with the james webb space telescope than oxygen or ozone biosignatures [2]. for nearby targets such as trappist-1e, 10 transits may be sufficient to detect co2, constrain ch4 abundances, and put an upper bound on co abundances [2]. an important question is whether there are non-biological scenarios that could generate the co2+ch4-co combination. here, we systematically explore potential false positives to either rule them out, or propose secondary observations to discrimante between biotic and abiotic cases. for example, we consider ch4 outgassing from highly reduced mantles, ch4 production via impacts, and serpentinization plus fischer-tropsch-like synthesis of ch4. the migration of volatile-rich, titan-like exoplanets into the habitable zone is another potential false positive. titan's interior is probably rich in co2 and ch4 but relatively co-depleted [3]. migrated titans could thus produce a false positive, although the duration of this would be limited by the photochemical lifetime of ch4. more problematic is the possible slow release of ch4 and co2 from high pressure ices which could maintain abundant atmospheric ch4 for several gyr [4]. we quantify all these scenarios and propose observational discriminants. [1] krissansen-totton, j., s. olson, and d. c. catling. science advances4.1 (2018): eaao5747. [2] krissansen-totton, j., r. garland, p. irwin & d. c. catling (2018). the astronomical journal. [3] tobie, g., d. gautier, and f. hersant. the astrophysical journal 752.2 (2012): 125. [4] levi, a., d. sasselov, and m. podolak. the astrophysical journal 792.2 (2014): 125. | are there false positives for a co2+ch4-co disequilibrium biosignature of an archean-like atmosphere? |
exoplanets around nearby small stars present the best opportunity forfuture atmospheric studies with the james webb space telescope and theground based elts under construction. the mearth project has discovered arocky planet with a period of 24.73 days residing in the habitable zone ofthe nearby, spun- down star lhs 1140. we seek to detect the high energyemission from lhs 1140 in order to constrain atmospheric escape and aidfuture studies of lhs 1140b's atmosphere, which are already planned in thejwst gto program. in addition, lhs 1140 is representative of the low mass,slowly rotating population of m dwarfs in the milky way. a deep x-rayexposure on this extremum of the stellar population will shed insightinto the magnetic dynamo and high energy processes ongoing in these stars. | assessing the high-energy environment of the habitable zone planet lhs 1140b |
editors note:in these last two weeks of 2017, well be looking at a few selections that we havent yet discussed on aas nova from among the most-downloaded paperspublished in aas journals this year. the usual posting schedule will resume in january.the threatening magnetic and plasma environment of the trappist-1 planetspublished july2017main takeaway:modelsof the magnetic environment surrounding the seven planets of the trappist-1 system suggest that this isnot a pleasant place to be for life. in particular, the simulations run bycecilia garraffo (harvard-smithsonian center for astrophysics) and collaborators indicate that all planets in the system are bombarded by a stellar wind with a pressure thats 1,000 to 100,000 times the pressureof what we experience on earth.why its interesting:simulations of the magnetic environment around the planet trappist-1 f, for a variety of different assumed planetary magnetic fields. red field lines are those that have connected between the star and the planet. [garraffo et al. 2017]the discovery of seven earth-sized planets in the nearby trappist-1 system particularly given many of the planets apparent location in the stars habitable zone gave us hope that these planets might be an interesting place to look for life. but the issue of habitability is more complicated than whether or not the planets can support liquid water. garraffo and collaborators models suggest that these planets likely have their atmospheres eroded or completely stripped by the stellar wind, renderingprospects for life on these planets low.why the trappist-1 systemis still awesome:we may be bummed that the magnetically active host star impedes chances for life on the trappist-1 planets, but theenvironment it produces isstill pretty awesome. according to the authors models, the planets pass through wildly changing wind pressure changes as they orbit. in the process, their magnetospheres are compressed, and their magnetic field lines connect with the stellar field lines over much of the planets surfaces, causing thestellar wind particles tofunnel directly onto the planets atmospheres. the result isan exciting and dynamic environment definitely worth studying further.citationcecilia garraffo et al 2017 apjl 843 l33. doi:10.3847/2041-8213/aa79ed | selections from 2017: hostile environment around trappist-1 |
we review a number of types of measurements that can be thought of in order to determine the presence of a solid surface and some relief on an exoplanet. we may be guided by the examples of remote sensing of planets mars, venus, and earth. spectroscopy allows to identify a gas and to measure its column abundance. if this gas is well mixed in the atmosphere (i.e., co2, o2, methane for titan), the column abundance is higher above regions of lower latitude, allowing a determination of altitude. acquiring some spatial resolution on the disc of the exoplanet requires telescopes of sizes of hundreds of kilometers, feasible with the concept of a diluted pupil. there are still some possibilities when the exoplanet is seen as a single-point, which will be the case for the next tens of years. both the cases of transiting and nontransiting planets are examined, with reflected star light or thermal emission. for transiting planets, the study of secondary eclipses (when the planet disappears progressively behind the star) is promising. however, it is pointed out that nontransiting exoplanets in the habitable zone of their host star are statistically three to nine times nearer the earth than transiting planets, enabling three to nine times smaller telescopes to achieve the same signal to noise ratio. | solid exoplanet surfaces and relief |
plato1 is an m-class mission of the european space agency's cosmic vision program, whose launch is foreseen by 2026. planetary transits and oscillations of stars aims to characterize exoplanets and exoplanetary systems by detecting planetary transits and conducting asteroseismology of their parent stars. plato is the next generation planetary transit space experiment, as it will fly after corot, kepler, tess and cheops; its objective is to characterize exoplanets and their host stars in the solar neighbors. while it is built on the heritage from previous missions, the major breakthrough to be achieved by plato will come from its strong focus on bright targets, typically with mv<=11. the plato targets will also include a large number of very bright and nearby stars, with mv<=8. the prime science goals characterizing and distinguishing plato from the previous missions are: the detection and characterization of exoplanetary systems of all kinds, including both the planets and their host stars, reaching down to small, terrestrial planets in the habitable zone; the identification of suitable targets for future, more detailed characterization, including a spectroscopic search for biomarkers in nearby habitable exoplanets (e.g. ariel mission scientific case, e-elt observations from ground); a full characterization of the planet host stars, via asteroseismic analysis: this will provide the community with the masses, radii and ages of the host stars, from which masses, radii and ages of the detected planets will be determined. | the design of the instrument control unit and its role within the data processing system of the esa plato mission |
trappist-1, a nearby ultracool dwarf star, was catapulted into the public eye roughly a year ago when it was determined to host seven transiting, earth-sized planets three of which are located in its habitable zone. but how correct are the properties weve measured for this system?trappist-1 is a very small, dim star its only 11% the diameter of the sun which makes it easier for us to learn about its planets from transit data. [eso]intrigue of trappist-1one reason the trappist-1 system is of particular interest to scientists is that its small star (roughly the size of jupiter) means that the system has a very favorable planet-to-star ratio. this makes it possible to learn a great deal about the properties of the planets using current and next-generation telescopes.the observations we expect to be able to make of trappist-1 exoplanets of the planet atmospheres, surface conditions, and internal compositions, for example will allow us to test planet formation and evolution theories and assess the prospects of habitability for earth-sized planets orbiting cool m dwarfs.why stellar measurements matterthe parallax motion of trappist-1 in dec (top) and r.a. (bottom) as a function of day. observations were made between 2013 and 2016 and then folded over a year. [van grootel et al. 2018]in order to make these measurements, however, we first need very precise measurements of the host stars parameters. this is because transiting exoplanet parameters are generally determined relative to those of the host. a few examples:determining how much irradiation a planet receives requires knowing the luminosity of the host star and planets orbit size. the latter is calculated based on the host stars mass.determining the planets radius requires knowing the host stars radius, as the planets transit depth tells us only the star-to-planet radius ratio.determining whether or not the planet is able to retain an atmosphere and therefore whether it has exhibited long-term habitability requires knowing the time the host star takes to contract onto the main sequence, which depends on the stars mass.when the trappist-1 planetary system was discovered, measurements of trappist-1s properties were made to the best of our abilities at the time. now, in a new study led by valrie van grootel (university of lige, belgium), a team of scientists has used new observations and analysis techniques to refine our measurements of the star.stellar luminosity for evolution models for various masses and metallicities. the green dashed horizontal lines bracket the authors observed value for trappist-1s luminosity. a stellar mass of 0.09 m is needed to account for the old age and luminosity of the star. [van grootel et al. 2018]new estimatesusing 188 epochs of observations of trappist-1 from multiple telescopes between 2013 and 2016, van grootel and collaborators obtained a very precise measurement for trappist-1s parallax. this allowed them to refine the estimate of its luminosity now measured at (5.22 0.19) x 10-4that of the sun to twice the precision of the previous estimate.the team then produced a new estimate for trappist-1s mass using new stellar evolution modeling and analysis, combined with empirical mass derived for similar ultracool dwarfs in astrometric binaries. this approach produces a final mass for trappist-1 of 0.089 0.006 m which is nearly 10% higher than the previous estimate and significantly more precise. finally, the authors use these values to obtain new estimates of trappist-1s radius (0.121 0.003 r) and effective temperature (2516 41 k).these new, refined measurements will ensure that our future observations of the trappist-1 planets are being interpreted correctly which is criticalfor a system that will be so thoroughly scrutinized in coming years. keep an eye out for new results about trappist-1 in the future!citationvalrie van grootel et al 2018 apj 853 30. doi:10.3847/1538-4357/aaa023 | pinning down properties of trappist-1 |
rocky exoplanets in the habitable zones (hz) of low mass stars will be prime targets for atmospheric characterization through transmission spectroscopy with the james webb space telescope (jwst). such planets are likely tidally locked, i.e. that their rotation period is synchronized with their orbital periods. the determination of the habitability of those worlds requires the use of 3d global climate models (gcms) to resolve the large-scale atmospheric circulation, heat transport, latitudinal and longitudinal water profiles and cloud coverage. previous studies have determined the inner edge of the hz for various low mass stars considering only a 1 bar background n2 pressure. however, the background pressure can significantly impact the planet's surface temperature, potentially enhance its habitability, by pressure broadening effects and n2-n2 collision induced absorption (cia). in this presentation, we show results from our gcm simulations using the community atmosphere model 4 (cam4), assuming a slab ocean configuration, for end member cases of low (0.25 bar) and high (10 bar) background n2 atmosphere. we compare our results of the inner edge of the habitable zone from kopparapu et al., (2017) study, who assumed a 1 bar n2 atmosphere. our results indicate that the assumed background pressure of n2 has a meaningful effect on climate, stratospheric water vapor mixing, and deduced observables. | the impact of background n2 pressure on the habitability of tidally locked rocky exoplanets around cool stars |
the most potentially observable habitable zone planets are found around m-dwarfs, therefore characterizing their long term atmospheric stability is important. ion loss in particular is critical to study because electric fields provide additional escape energy to heavy species that could make up volatile rich atmospheres. we used a global hybrid plasma model to systematically study how ion escape processes vary from solar system expectations due to the extreme conditions found at the habitable zone of a typical m-dwarf. to isolate the effects of different stellar influence properties we incrementally changed each parameter, allowing our interpretation to be more generalizable across systems. we found that while both the ion loss morphology and rates were dictated by the resultant plasma environment, there was not a straightforward relationship between energy input and ion outflow due to ion production limitations. it is thus important to consider under what conditions scaling laws derived by observations of solar system planets begin to break down when applied to more extreme environments. additionally, the asymmetric plasma environment created by a nearly flow aligned interplanetary magnetic field lead to asymmetric ion outflow, possibly creating observable atmospheric asymmetry in tidally locked planets. we also investigated the influence of intrinsic planetary magnetic field on the ion escape. although terrestrial planets around m-dwarfs are likely to be un- or weakly-magnetized, even a weak magnetic field is capable of changing the dynamics of the solar wind interaction. our results reflect a balancing act between magnetic standoff pressure and polar outflow, where the presence of a magnetic field enhances escape to a certain point before beginning to inhibit it. | heavy ion escape from terrestrial exoplanets |
water-worlds are water-rich (>1% water by mass) exoplanets. if located at an appropriate orbital separation from their host star (i.e. in the habitable zone) they may have the potential to host a global surface water ocean. water-worlds likely accrete a comet-like mixture of volatiles, leading to co2-rich compositions, with between ~3 mol% to ~30 mol% co2 relative to water. in this study, we constrain the hydrosphere structures, co2 contents and co2 reservoirs in the interiors of water-worlds. we couple a sophisticated equation of state that accurately reproduces experimental phase boundaries of co2-h2o mixtures to models of planet interior structure and atmospheric radiative transfer. we determine that neither the atmosphere, ocean, nor clathrate layer (if present) can be the main co2 reservoir on habitable (liquid ocean-bearing) water-worlds that accreted more than 11 wt% volatiles. the largest potential reservoir of co2 inside of habitable water-world hydrospheres is likely to be co2 ice trapped in the high-pressure water ice mantle. consequently, the atmospheric composition of a water-world does not necessarily reflect the total mass of volatiles accreted during the formation of the planet, nor the relative proportions of co2 and h2o in the hydrosphere. instead, the co2 molar fraction in the atmosphere is determined by the post-accretional cooling history of the planet. detailed modeling of the post-accretional cooling of water-worlds is needed to determine whether co2 ice burial could allow water-worlds to have liquid water oceans or whether the evolution of the planet would generically lead to too much atmospheric co2 for the planets to be habitable. | internal structure and co2 reservoirs of habitable water-worlds |
in this work, we propose a methodology to assess planetary surface habitability for any newly discovered exoplanet lying in the habitable zone of a low mass, superflare, main-sequence star. while habitability is usually a function of multiple parameters (i.e. the size of the planet, the composition of its atmosphere, the existence of liquid water, orbital or rotational dynamics), the presented method primarily focuses on stellar activity and its effects on potentially existing planetary magnetospheres stemming from dynamo-generated magnetic fields. the area our method applies to, is split in two regimes depending on whether the exoplanet of interest is tidally locked or tidally unlocked to its mother star. in the former case, a ratio between a conditional (beq) and a best-case equatorial planetary magnetic field (bstev), is calculated. a smaller-than-unity value of that ratio favors the formation of a stable atmosphere adequate to host surface, atmosphere-dependent habitability. in the latter case (tidally unlocked regime), a ratio between a conditional (beq) and the terrestrial magnetic field (bearth) is estimated, which indirectly implies how easy or hard it is for an exoplanet to sustain an atmosphere. for a ratio's value lower than unity, there is hope for surface habitability since its magnetic field is assumed equal to, or larger than, the terrestrial one. on the other hand, a value higher than one casts doubts on surface habitability, because even a strong, terrestrial magnetic field is not sufficient to secure an atmosphere for the exoplanet. both ratios concerning the two different spatial regimes of our method's application are based on the observed mother star's activity and are calculated on the critical magnetopause distance of two planetary radii, below which atmospheric erosion phenomena are assumed to start taking place. | a method to assess planetary habitability based on the effects of cme magnetic fields on planetary magnetospheres |
one of the most exciting results from alma has been the detection of significant substructure within protoplanetary disks that can be linked to planet formation processes. for the first time, we are able to observe the process of assembly of material into larger bodies within such disks. it is not possible, however, for alma to probe the growth of planets in protoplanetary disks at small radii, i.e., in the terrestrial zone, where we expect rocky terrestrial planets to form. in this regime, the optical depths prohibit observation at the high frequencies observed by alma. to probe the effects of planet building processes and detect telltale gaps and signatures of planetary mass bodies at such small separations from the parent star, we require a facility of superior resolution and sensitivity at lower frequencies. the ngvla is just such a facility. we will present the fundamental science that will be enabled by the ngvla in protoplanetary disk structure and the formation of planets. in addition, we will discuss the potential for an ngvla facility to detect the molecules that are the building blocks of life, reaching limits well beyond those reachable with the current generation of telescopes, and also to determine whether such planets will be habitable based on studies of the impact of stars on their nearest planetary neighbours. | terrestrial zone exoplanets and life |
transit spectroscopy of terrestrial planets around nearby m dwarf host stars is a primary goal of space missions in the coming decades. 3-d climate modeling has shown that slowly rotating terrestrial extrasolar planets, at the inner edge of their habitable zones (hz), may possess significantly enhanced stratospheric water vapor compared to a rapidly rotating planet like earth. for 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. 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 dwarf stars. 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. | the impact of stellar uv activity on habitable moist terrestrial exoplanet atmospheres around m dwarfs |
m-dwarf stars are prime targets for exoplanet searches because of their close proximity and favorable properties for both planet detection and characterization, with current searches around these targets having already discovered several earth-sized planets within their star’s habitable zones. however, the atmospheric characterization and potential habitability of these exoplanetary systems depends critically on the high-energy stellar radiation environment from x-rays to nuv. strong radiation at these energies can lead to atmospheric mass loss and is a strong driver of photochemistry in planetary atmospheres. recently, the muscles treasury survey provided the first comprehensive assessment of the high-energy radiation field around old, planet hosting m-dwarfs. however, the habitability and potential for such exoplanetary atmospheres to develop life also depends on the evolution of the atmosphere and hence the evolution of the incident radiation field. the strong high-energy spectrum of young m-dwarfs can have devastating consequences for the potential habitability of a given system. we, thus, introduce the far ultraviolet m-dwarf evolution survey (fumes), a new hst-stis observing campaign targeting 10 early-mid m dwarfs with known rotation periods, including 6 targets with known ages, to assess the evolution of the fuv radiation, including lyα, of m-dwarf stars with stellar rotation period. we present the initial results of our survey characterizing the fuv emission features of our targets and the implications of our measurements for the evolution of the entire high-energy radiation environment around m-dwarfs from youth to old age. | the far ultraviolet m-dwarf evolution survey (fumes): overview and initial results |
the sun-earth systems has long been used as a template to understand habitable planets around other stars and to develop missions to seek them. however, two decades of exoplanet studies have shown that many, if not most planetary systems around g dwarf stars do not resemble the solar system. moreover, an objective census of our galaxy might ignore solar- type stars and focus on m dwarfs, which constitute some 80% of all stars in the neighborhood. recent work has shown that m dwarfs have more close-in planets than solar-type stars, and perhaps more planets in the "habitable zone" defined by stellar irradiation. m dwarfs also burn hydrogen over a vastly longer time; slow evolution on the main sequence means a planet can remain habitable for much longer, providing a more permissive environment for the evo- lution of life and intelligence. if m dwarfs are such compelling locales to look for life, why are we ourselves not orbiting a red sun? | seek a minor sun: the distribution of habitable planets in the hertzsprung-russell-rosenberg diagram |
m-dwarfs are the most common type of stars in our galaxy. ultra-cool dwarfs (t < 2700 k) are a sub-stellar class of late m-dwarfs and represent nearly ~ 15% of astronomical objects in the stellar neighborhood of the sun. their smaller size than regular m-dwarfs allows easier detection of rocky exoplanets in close orbits, and this potential was recently realized by the discovery of the trappist-1 system. located about 12 pc away, trappist-1 has seven known planets, and it is one of the most promising rocky-planet systems for follow-up observations due to the depths of the transit signals. transit-timing variation (ttvs) measurements of the trappist-1 planets suggest terrestrial or volatile-rich composition. also, it has been found that three planets (trappist-1 e, f and g) are in the habitable zone (hz) where surface temperatures would allow surface water to exist. these planets will be prime targets for atmospheric characterization with jwst owing to their relative proximity to earth and frequent planetary transits.atmospheric properties are major components of planet habitability. however, the detectability of gaseous features on rocky planets in the hz may be severely impacted by the presence of clouds and/or hazes in their atmosphere. we have already seen this phenomenon in the “flat” transit transmission spectra of larger exoplanets such as gj 1214b, wasp-31b, wasp-12b and hatp-12b.in this work, we use the lmdg global climate model to simulate several possibilities of atmospheres for trappist-1 e, f and 1g: 1) archean earth, 2) modern earth and 3) co2-dominated atmospheres. we also calculate synthetic transit spectra using the gsfc planetary spectrum generator (psg), and determine the number of transits needed to observe key spectral features for both jwst and future telescopes (ariel, luvoir, habex). we will identify differences in the spectra of cloudy vs non-cloudy, and determine how much information on spatial variability in atmosphere characteristics can be extracted from time-resolved transit and eclipse mapping. a particular attention will be given to the impact of the atmospheric variability when adding transit spectra, and how this may affect atmospheric parameter retrievals. | impact of clouds in the jwst and luvoir simulated transmission spectra of trappist-1 planets in the habitable zone |
superconducting nanowire single-photon detectors (snspds) have emerged as the highest-performing single-photon detectors from the uv to the mid-infrared. these detectors combine very high efficiencies (> 90% in the infrared at 1.55 um), ultralow jitter ( 100 ps or less), zero readout noise, and very low dark count rates ( < 10-4 hz) . recently, we have developed snspds operating in the mid-infrared from 2 - 7 um. basic models of the physics of the detection process suggest that by reducing the width of the nanowires to 10 - 20 nm, and tuning the composition of the superconducting material, one may be able to demonstrate single-photon detection at wavelengths extending to 60 um. in addition, recently-developed multiplexing techniques should allow the fabrication of small arrays consisting of 1000 pixels or more, which could potentially be useful for spectroscopy and imaging. the primary advantages of using snspds in this wavelength range are high stability of detector gain as a function of temperature and bias current, true single-photon sensitivity, zero readout noise, and extremely low dark count rate. in addition, snspds would not suffer from many of the problems inherent with arrays of currently used blocked impurity band (bib) detectors such as reset anomaly, last-frame effect, droop, drift, multiplexer glow, and latent images. one of the many goals of the origins space telescope (ost) is the study of exoplanets. this study makes up roughly one-third of the science case for ost. in particular, part of ost's mission is the detection of biosignatures such as ozone, nitrous oxide, and methane in the atmospheres of earth-sized planets transiting the habitable-zones of nearby stars. the spectroscopy of exoplanet atmospheres requires mid-infrared detector arrays combining high stability over time (a few ppm over several hours), high sensitivity (ideally single-photon sensitive), high system efficiency, and low noise. we propose to develop kilopixel-scale arrays consisting of single-photon-sensitive superconducting nanowire detectors that are sensitive in the range of 6 - 20 um wavelengths that would meet the requirements for any future instruments directed towards exoplanet transit spectroscopy, for example the mid-infrared spectrometer and coronagraph (misc) planned for the origins space telescope. as outlined above, the excellent stability and single-photon sensitivity of these detectors would be ideal for such an application requiring data collection over the course of hundreds of transits of an exoplanet across its parent star, each of which can last several hours or longer. | superconducting nanowire single-photon detectors for exoplanet spectroscopy in the mid-infrared |
more than 50 planets are discovered with the different ground based telescopes available for microlensing. but the analysis of ground based data fails to provide a complete solution. to fulfill that gap, space based telescopes, like hubble space telescope and spitzer are used. my research work focuses on extracting the planet mass, host star mass, their separation and their distance in physical units from hst follow-up observations. i will present the challenges faced in developing this method.this is the primary method to be used for nasa's top priority project (according to 2010 decadal survey) wide field infrared survey telescope (wfirst) exoplanet microlensing space observatory, to be launched in 2025. the unique ability of microlensing is that with wfirst it can detect sub-earth- mass planets beyond the reach of kepler at separation 1 au to infinity. this will provide us the necessary statistics to study the formation and evolution of planetary systems. this will also provide us with necessary initial conditions to model the formation of planets and the habitable zones around m dwarf stars. | wfirst microlensing exoplanet characterization with hst follow up |
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 ascertain the truth is to make a measurement. i will also present how a survey of nearby mid-to-late m dwarfs could empirically determine the fraction of habitable-zone planets that develop life. | detecting atmospheric biosignatures of transiting exoplanets in the mid-ir |
water worlds are water-rich (>1% water by mass) exoplanets. they may form from volatile-rich material beyond the snow line but never attain masses sufficient to accrete or retain large amounts of h2/he nebular gas. this pathway for producing low-mass water-rich planets has played out as a robust prediction of planet formation simulations, and may produce planets with comet-like compositions having up to 50% of their mass in astrophysical ices. if located at an appropriate orbital separation from their host star, water worlds may possess a global surface water ocean. habitable (liquid ocean-bearing) water worlds are especially timely because their larger sizes relative to terrestrial planets make them more amenable to observations with current and upcoming telescopes such as hubble space telescope (hst) and james webb space telescope (jwst). the classic calculations of the habitable zone consider earth-like planets, where the amount of co2 in the atmosphere is stabilized by the carbonate-silicate cycle. due to their important oceanic mass, the hydrostatic pressure at the oceanic floor of water worlds reaches the stability field of high pressure polymorphs of water ice, hindering chemical interactions between the liquid water and the silicates. in the absence of a carbonate-silicate cycle, the solubility of co2 in the ocean and the formation of co2-rich clathrates determine the concentration of co2 in the water world's atmosphere. we use gerg-2008 equation of state for co2-h2o mixture and coupled models of planet interior structure, clathrate formation, liquid-vapor equilibrium, and atmospheric radiative transfer to constrain the atmospheric and interior co2 abundances of habitable water worlds. we show that for a habitable water world with more than 11 wt% volatiles, the vast majority of its co2 needs to be trapped in the interior of the planet. in order for these planets to have a cometary, co2-rich composition and remain habitable, we propose that they may possess a significant fraction of co2 trapped as co2 ice inside of the high-pressure water ice mantle. | internal structure and co2 reservoirs of habitable water-worlds |
kepler has to date discovered 4,496 exoplanet candidates, but only half are confirmed, and only a handful are thought to be earth sized and in the habitable zone. planet verification often involves extensive follow-up observations, which are both time and resource intensive. the data set collected by kepler is massive and will be studied for decades. university/small observatories, such as the one at texas state university, are in a good position to assist with the exoplanet candidate verification process. by preforming extended monitoring campaigns, which are otherwise cost ineffective for larger observatories, students gain valuable research experience and contribute valuable data and results to the scientific community. | conducting research from small university observatories: investigating exoplanet candidates |
we propose to take advantage of the stis coronagraphic mode and advances in speckle subtraction techniques to probe for scattered light from epsilon eridani's predicted asteroid belt analog. this proposal tests for the presence of visible scattered light from a warm dust ring at 1 arcsecond with a 5e-5/as^2 contrast, predicted from observations of the 24 micron excess. dust morphology and scattered light brightness (exozodi) present a significant challenge to future exoplanet imaging missions, and epsilon eridani is an excellent sunlike candidate for future exoplanet direct imaging missions due its easily accessible habitable zone.either a detection of scattered light from this circumstellar dust population or a non-detection will place valuable constraints on the dust composition, morphology, and transport mechanisms at work in the system and inform future direct imaging efforts of this nearby star system. | imaging the predicted asteroid belt analogue around epsilon eridani |
space-based telescope mission concepts currently under development by nasa would be capable of directly imaging exoplanets within the habitable zones of their host stars. the spectroscopic data from such missions could provide an opportunity to detect biosignatures. the strongest remotely detectable signature of life on our planet today is the photosynthetically produced oxygen (o2) in our atmosphere. however, recent studies of earth’s geochemical proxy record suggest that for all but the last ~500 million years, atmospheric o2 would have been undetectable to a remote observer, a potential false negative for life. during an extended period in earth’s middle history (2.0 - 0.7 billion years ago, ga), o2 was likely present but in low concentrations, with po2 estimates of ~ 0.1 - 1% of present-day levels. recent biogeochemical modeling results have suggested methane (ch4) was likewise undetectably low during this period. although o2 has a weak spectral impact in reflected light at abundances consistent with earth’s middle history, o3 in photochemical equilibrium with that o2 would produce notable spectral features in the uv hartley-huggins band (~0.25 µm), with a weaker impact in the mid-ir band near 9.7 µm. thus, taking earth history as an informative example, there likely exists a category of exoplanets for which conventional biosignatures can only be identified in the uv. we use simulated observations to emphasize the importance of uv capabilities in the design of future space-based direct imaging telescopes such as habex or luvoir to detect o3 on planets with weakly oxygenated states. we also show that under low-o2 conditions, seasonal variations in o2 production and consumption by the biosphere could manifest as time-variable o3. such seasonality in the hartley-huggins band provides both an opportunity and a challenge for remote life-detection studies because this biosignature may only be detectable intermittently over a planet’s orbital period. these examples highlight the importance of uv capability for future direct-imaging telescopes and illustrate the broad implications of studying earth history as a window into understanding potential exoplanet biosignatures. | assessing ozone detectability on weakly oxygenated terrestrial exoplanets |
our global models show that atmospheres of terrestrial type exoplanets around m dwarfs are vulnerable to high xuv fluxes and magnetized winds causing atmospheric loss rate of o and n, which will make exoplanets uninhabitable within 10-100 myr. | space weather affected habitable zones |
precise measurements of doppler shifts of lines in stellar spectra allowing the radial velocity to be measured are an important field of astrophysical studies. a remarkable feature of the doppler spectroscopy is the possibility to reliably measure quite small variations of the radial velocities (its acceleration, in fact) during long periods of time. influence of a planet on a star is an example of such a variation. under the influence of a planet rotating around a star, the latter demonstrates periodic motion manifested in the doppler shift of the stellar spectrum. precise measurements of this shift made it possible to indirectly discover planets outside the solar system (exoplanets). along with this, searching for earth-type exoplanets within the habitable zone is an important challenge. for this purpose, accuracy of spectral measurements has to allow one to determine radial velocity variations at the level of centimeters per second during the timespans of about a year. suchmeasurements on the periods of 10-15 years also would serve as a directmethod for determination of assumed acceleration of the universe expansion. however, the required accuracy of spectroscopic measurements for this exceeds the possibilities of the traditional spectroscopy (an iodine cell, spectral lamps). methods of radical improvement of possibilities of astronomical doppler spectroscopy allowing one to attain the required measurement accuracy of doppler shifts are considered. the issue of precise calibration can be solved through creating a system of a laser optical frequency generator of an exceptionally high accuracy and stability. | methods of laser, non-linear, and fiber optics in studying fundamental problems of astrophysics |
this paper provides an overview of technology development for the terrestrial planet finder interferometer (tpf-i). tpf-i is a mid-infrared space interferometer being designed with the capability of detecting earth-like planets in the habitable zones around nearby stars. | technology challenges for exoplanet detection with mid-ir interferometry |
there is renewed interest in understanding the low mass stars and brown dwarfs of the solar neighborhood. since m dwarfs make up the vast majority of stars in the universe, it is essential that we understand their fundamental physical properties. their ubiquitousness makes them excellent kinematic and chemical probes of the galaxy, provided we can accurately measure their distances, absolute magnitudes, and metallicities. additionally, current and future exoplanet surveys that are focused on m dwarfs, such as spirou, carmenes, and the habitable zone planet finder will uncover a plethora of planetary systems around these stars. unfortunately, many of the nearby low mass stars are poorly characterized with current data. the mearth survey has been monitoring approximately 1800 mid-to-late m dwarfs since 2008 and each night also observes a set of landolt standard stars. we measure a precise optical magnitude in our mearth bandpass, a red broadband filter similar to the bessel i filter, for 1500 of these systems. by combining this work with our recent work measuring the trigonometric parallaxes and metallicities of a subset of these m dwarfs, we construct a photometric metallicity relation. we then apply it to the full sample of mearth-north m dwarfs.the mearth project gratefully acknowledges funding from the david and lucile packard fellowship for science and engineering, the national science foundation under grants ast-0807690, ast-1109468, and ast-1004488, and the john templeton foundation. | absolute optical photometry and a photometric metallicity relation for the nearby cool stars from the mearth project |
low-mass stars are the dominant planet hosts averaging about one planet per star. many of these planets orbit in the canonical habitable zone (hz) of the star where, if other conditions allowed, liquid water may exist on the surface.a planet’s habitability, including atmospheric retention, is strongly dependent on the star’s ultraviolet (uv) emission, which chemically modifies, ionizes, and even erodes the atmosphere over time including the photodissociation of important diagnostic molecules, e.g. h2o, ch4, and co2. the uv spectral slope of a low-mass star can enhance atmospheric lifetimes, and increase the detectability of biologically generated gases. but, a different slope may lead to the formation of abiotic oxygen and ozone producing a false-positive biosignature for oxygenic photosynthesis. realistic constraints on the incident uv flux over a planet’s lifetime are necessary to explore the cumulative effects on the evolution, composition, and fate of a hz planetary atmosphere.nasa’s galaxy evolution explorer (galex) provides a unique data set with which to study the broadband uv emission from many hundreds of m dwarfs. the galex satellite has imaged nearly 3/4 of the sky simultaneously in two uv bands: near-uv (nuv; 175-275 nm) and far-uv (fuv; 135-175 nm). with these data these, we are able to calculate the mean uv emission and its level of variability at these wavelengths over critical planet formation and evolution time scales to better understand the probable conditions in hz planetary atmospheres.in the near future, dedicated cubesats (miniaturized satellites for space research) to monitor m dwarf hosts of transiting exoplanets will provide the best opportunity to measure their uv variability, constrain the probabilities of detecting habitable (and inhabited) planets, and provide the correct context within which to interpret ir transmission and emission spectroscopy of transiting exoplanets. | the high-energy radiation environment of planets around low-mass stars |
the relatively low temperatures (~2-4 kk), small radii, and sheer abundance make m dwarfs favorable candidates for planet detection and atmospheric characterization. current models for the habitable zone are determined by the host star luminosity and rarely include contributions from flaring. stellar flares, which occur when the coronal magnetic field reorganizes to a lower energy state, release panchromatic radiation which has a significantly higher brightness temperature (~9-20 kk) than the star. the excess ultraviolet contribution has strong implications for observable exoplanetary phenomena such as atmospheric loss and induced photochemistry. increased magnetic activity on m dwarfs results in energy released during flaring events becoming a notable contributor to the radiation environment. consequently characterizing the evolution of flare properties is crucial to understand the planetary context that is needed to interpret observations of exoplanet atmospheres. the beta pictoris moving group (24 ± 3 myr) provides an optimal starting point for the analysis of young low mass star flaring rates within the framework of larger flare studies in which effects due to metallicity and age become less pronounced. with >40 viable m dwarf members, including the multi-planet system host au mic, we use tess observations to identify and characterize flare properties of these stars such as total energy and cumulative flare rate. we present an initial analysis of this population and their potential insight into the co-evolution of host stars and associated planets. work to expand this analysis into other well-populated and observationally accessible moving groups and therefore different ages is ongoing. results from this study will assist in determining how changes in flare properties over time impact the atmospheric evolution of exoplanets. | analysis of young m dwarf flaring with the beta pictoris moving group |
the habitable zone gallery (www.hzgallery.org) came online in august 2011 as a service to the exoplanet community that provides habitable zone (hz) information for each of the exoplanetary systems with known planetary orbital parameters. the service includes a sortable table, a plot with the period and eccentricity of each of the planets with respect to their time spent in the hz, a gallery of known systems which plot the orbits and the location of the hz with respect to those orbits, and orbital movies. recently, we have added new features including: implementation of both conservative and optimistic hzs, more user-friendly table and movies, movies for circumbinary planets, and a count of planets whose orbits lie entirely within the system's hz. here we discuss various educational and scientific applications of the site such as target selection, exploring planets with eccentric or circumbinary orbits, and investigating habitability. | what can the habitable zone gallery do for you? |
recent works suggest that oxygen can be maintained on lifeless exoplanets in the habitable zones of m dwarfs as the results of photochemical reactions. however, the same photochemical models also predict high concentrations of carbon monoxide (co) in the corresponding atmospheres. a line-by-line radiative transfer model is used to investigate observation requirements of o2 and co. we find that abiotically produced o2 is detectable at 0.76 μm, in agreement with previous findings. more interestingly co in the corresponding atmospheres is also detectable at nir. we suggest that future missions aiming at characterization of exoplanetary atmospheres consider detections of co as an anti-biosignature. | on the detection of carbon monoxide as an anti-biosignature in exoplanetary atmospheres |
uv stellar radiation can significantly impact planetary atmospheres through heating and photochemistry, even regulating production of potential biomarkers. cool stars emit the majority of their uv radiation in the form of emission lines, and the incident uv radiation on close-in habitable-zone planets is significant. lyα (1215.67 å) dominates the 912 - 3200 å spectrum of cool stars, but strong absorption from the interstellar medium (ism) makes direct observations of the intrinsic lyα emission of even nearby stars challenging. the muscles hubble space telescope treasury survey (measurements of the ultraviolet spectral characteristics of low-mass exoplanetary systems) has completed observations of 7 m and 4 k stars hosting exoplanets (d < 22 pc). we have reconstructed the intrinsic lyα profiles using an mcmc technique and used the results to estimate the extreme ultraviolet (100 - 911 å) spectrum. we also present empirical relations between lyα and chromospheric uv metal lines, e.g., mg ii, for use when ism absorption prevents direct measurement of lyα. the spectra presented here will be made publicly available through mast to support exoplanet atmosphere modeling. | intrinsic lyα profile reconstructions of the muscles low-mass exoplanet host stars |
although the hubble space telescope (hst) and the james webb space telescope (jwst) were not initially conceived for the study of planets beyond our solar system, they will be the workhorses of exoplanet atmospheric characterization in the early 2020s. for more than a decade, hst has provided the exoplanet community with spectroscopic access to exoplanet atmospheres in the uv through nir, revealing a broad range of physical and chemical processes at work in these distant worlds. exoplanet observations with hst have produced a number of ground-breaking first, including the first detection of an exoplanet atmosphere, that will leave a lasting legacy in exoplanet science. jwst will for the first time provide the exoplanet community with space-based spectroscopic and coronagraphic capabilities in the ir, thus unlocking key molecular signatures and probing the thermal emission from these planets. it is also expected that jwst will provide unprecedented sensitivity and precision that will allow deep exploration of a broad range of exoplanets, including those in the habitable zone of their host stars. broad wavelength coverage, from the uv to the ir, is critical to understanding the physics and chemistry at work in exoplanet atmospheres as well as other processes in exoplanetary systems. in the 2020s, hst and jwst will offer some of the best spectroscopic and photometric probes of exoplanets available. here i will highlight the legacy of hst and the future with jwst for exoplanet science. | the harvest of hst exoplanet science and the prospect of jwst |
we are standing on the cusp of a major discovery in planetary sciences. for the first time in human history, upcoming surveys and telescopes working together will be able to remotely detect potential biosignatures in exo-earth atmospheres and discover signs of life beyond our solar system. in order to make the most of the near-future observational opportunities, optimal target selection will be of the utmost importance. selection of targets for this characterisation relies on the ambiguously defined concept of habitability, which is currently constrained by only the density of the planet and the distance from its host star. with the expected increase in the number of detected exoplanets from tess, we might end up with hundreds of planets that suit these criteria and are accordingly all equally likely to host life. therefore, we must rethink our classification of what makes a planet habitable. on earth plate tectonics and planetary magnetism are postulated to play an integral role in planetary temperature regulation and protection from solar winds and flares and are a critical component in supporting conditions for long-term surface liquid water. we utilise jackson et al. 's (2008) equations to model tidal heating and olson & christensen's (2006) model to estimate magnetic dipole moments of rocky exoplanets with radii r$ _{p}$ $\le$≤ 1.23 r$_\oplus$. when examining exoplanets located within the circumstellar habitable zone, only trappist-1f, trappist-1g, ross 128 b, and proxima cen b were within the range where there is enough tidal heating for plate tectonics to occur, but not to the extent that it escalates to extreme planet-wide volcanism. additionally, when modelling maximum magnetic dipole moments, only kepler-186 f has a magnetic dipole moment larger than the earth's, and only 22% $\pm$ 1% of rocky exoplanets detected in the circumstellar habitable zone have a dipole moment sufficient to support long-term liquid water. furthermore, combining the two habitability factors - plate tectonics and planetary magnetism - trappist-1 g shows the highest potential to have both the presence of plate tectonics and a magnetic field sufficiently strong to preserve surface liquid water. continuing to expand to a multi-parameter approach to habitability (m-path) by including factors such as magnetic field, plate tectonics, albedo, stellar type, orbit characteristics, tidal locking, and impact events, will enable us to prioritise planets most likely to maintain liquid water. by analysing, modelling, and constraining how these factors interact on any given planetary body, we can generate a flexible framework for prioritisation involving multiple observable characteristics that influence continuous planetary habitability. based on the results, we will be able to provide a revised model of planetary habitability and suggest a suitable strategy for future astrobiological and biosignature observations of life in the universe. in conjunction with the rapidly increasing information from exoplanet databases expected within the next decade, this research will help determine optimal targets for near-future ground- and space-based spectroscopic observations of planetary atmospheres and the possible detection of life in space. | multi-parameter approach to habitability (m-path) |
m dwarfs are the most abundant stellar type in our galaxy and the most common type of exoplanet host star. the ongoing transiting exoplanet survey satellite (tess) mission is an all-sky mission designed to detect planets around nearby, bright stars. with its high-cadence, high-precision photometry, tess has revolutionized the study of stellar activity of low mass stars. i will present my work on the detection and characterization of planets orbiting low mass stars. first, i will discuss the discovery of the toi-700 planets, including toi-700 d, the first habitable zone, earth-sized planet discovered with tess. i will describe our collaboration's ongoing work to further characterize this system. next, i will discuss my research characterizing the pre-main sequence m dwarf, au mic. au mic exhibits significant variability in its light curve in the form of spot modulation and flares. both of these features complicate the transit fits for au mic b and c, but by fitting the activity and transits simultaneously, i am able to construct accurate transit models, and therefore derive precise planet radii. as a part of this work, i also model the spots and white light flare to study the activity from au mic, and i demonstrate the value of tess 20-second cadence data for modeling flares and transits. finally, i model the optical flares of proxima centauri observed by tess in order to conduct a transit search across the entire habitable zone of the star. while no transiting planets are detected, my flare removal increases the transit sensitivity by 60%. this method has great potential for searching active m dwarf stars observed by tess to identify small planets that may be masked by stellar flares. | the detection and characterization of planets around m dwarf stars |
microlensing is a key technique for the search and the characterization of exoplanets, with the ultimate goal to understand their formation mechanism. here i report on two space-based programs. the main scientific goal of the ongoing spitzer program is to measure the galactic distribution of exoplanets towards the bulge. the primary science goal of the forthcoming wfirst microlensing survey is to ``complete the statistical census of planetary systems in the galaxy, from the outer habitable zone to free floating planets, including analogs of all of the planets in our solar system with the mass of mars or greater.''. | exoplanets and space-based microlensing: the galactic distribution of exoplanets with the spitzer program and the statistical census of planets with the wfirst survey. |
venus analogs discovered in the coming years will be crucial to constraining the parameters that we use to define the habitable zone and venus zone. | identifying potential venus analogs from exoplanet discoveries |
the search for an earth analog within the habitable zone of a sun-like star requires a radial velocity (rv) precision of ~10 cm s^-1. previous generation instrumentation and data analysis techniques paved the way for precision rv measurements, allowing for detections on the order of 1 m s^-1. while the community is working to break the 1 m s^-1 barrier with further advancement in instrumentation and analysis, we also remain limited in our small planet detection capabilities by the presence of stellar noise, produced by oscillations, granulation and magnetic activity. these phenomena cause signatures in rv measurements that can effectively obscure the detection of small-mass exoplanets. therefore, we must also address the 1 m s^-1 barrier by better understanding how to mitigate stellar noise. in this work, we focus on how rv observing strategy can be used to mitigate the effects of stellar noise, by quantitatively determining the strategy that yields the best rv precision (lowest rms). this work builds on that of dumusque et al. (2011), but uses "traditional" (planet-finding) rv observations, instead of those obtained for asteroseismology, and also covers a longer observing period. our data consist of high cadence rv measurements of three stars with spectral types f and g, taken between march 2017 and may 2018 with the planet finder spectrograph (pfs) installed on the 6.5 m magellan ii telescope at las campanas observatory in chile. we apply various binning schemes to these data and calculate the resulting rms from each binning scheme. we find that not only do stars of different spectral types have different optimal observing strategies, but such is the case for even stars of the same spectral type, suggesting that granulation size and decay time may depend on more than effective temperature. | mitigating stellar noise using high cadence radial velocity observations |
aiming for examining the habitable zone around stars, we have been examining the conditions which determine where the inner-edge of habitable zone lies using our atmospheric general circulation model (agcm), dcpam5 (http://www.gfd-dennou.org/library/dcpam). in this presentation, we will show results of two series of experiments using dcpam5: (1) aquaplanet series using aquaplanet condition that all surface is covered with ocean, (2) land planet series using land planet condition that all surface is land with small amount of soil moisture. for aquaplanets, the runaway greenhouse state (nakajima et al., 1992) has been discussed as an important concept for determining the inner-edge of habitable zone. some agcm experiments have shown that non-equilibrium states in which atmospheric temperature keeps increasing are obtained with increased incident flux (e.g., leconte et al., 2013). as for land planets, abe et al. (2011) discussed that complete evaporation of all surface water occurs on land planets with incident flux more than 1.7 times of present earth's value, and that the critical value of incident flux determines inner-edge of habitable zone. above described previous studies did not examine the dependence of inner-edge of habitable zone on parameters such as planetary rotation rate. since large scale atmospheric circulation structure, and hence atmospheric water vapor distribution, change according to the values of planetary rotation rate, the condition for determining inner-edge can change according to values of planetary rotation rate. in order to examine this problem, we performed agcm experiments for various values of solar constant and planetary rotation rate. our results of aquaplanet series show that the occurrence condition of the runaway greenhouse state can be described by the upper limit of planetary radiation regardless the value of planetary rotation rate. the results of land planet series experiments show the possibility that inner-edge of habitable zone for land planet lies closer to stars than that estimated by abe et al. (2011). | numerical experiments on climate of terrestrial exoplanets: aquaplanet and land planet |
rocky exoplanets are typically classified as potentially habitable planets, if liquid water exists at the surface. the latter depends on several factors like the abundance of water but also on the amount of available solar energy and greenhouse gases in the atmosphere for a sufficiently long time for life to evolve. the range of distances to the star, where surface water might exist, is called the habitable zone. here we study the effect of the planet interior of stagnant-lid planets on the formation of a secondary atmosphere through outgassing that would be needed to preserve surface water. we find that volcanic activity and associated outgassing in one-plate planets is strongly reduced after the magma ocean outgassing phase, if their mass and/or core-mass fraction exceeds a critical value. as a consequence, the effective outer boundary of the habitable zone is then closer to the host star than suggested by the classical habitable zone definition, setting an important restriction to the possible surface habitability of massive rocky exoplanets, assuming that they did not keep a substantial amount of their primary atmosphere and that they are not in the plate tectonics regime. | volcanism and outgassing of stagnant-lid planets: implications for the habitable zone |
in recent work [1] we demonstrated that the climatic history of venus may have allowed for surface liquid water to exist for several billion years using a 3d gcm [2]. model resolution was 4x5 latitude x longitude, 20 atmospheric layers and a 13 layer fully coupled ocean. several assumptions were made based on what data we have for early venus: a.) used a solar spectrum from 2.9 billion years ago, and 715 million years ago for the incident radiation. b.) assumed venus had the same slow modern retrograde rotation throughout the 2.9 to 0.715 gya history explored, although one simulation at faster rotation rate was shown not to be in the hz. c.) used atmospheric constituents similar to modern earth: 1 bar n2, 400ppmv co2, 1ppmv ch4. d.) gave the planet a shallow 310m deep ocean constrained by published d/h ratio observations. e.) used present day venus topography and one run with earth topography.in all cases except the faster rotating one the planet was able to maintain surface liquid water. we have now inserted the socrates [3] radiation scheme into our 3d gcm to more accurately calculate heating fluxes for different atmospheric constituents. using socrates we have explored a number of other possible early histories for venus including: f.) an aquaplanet configuration at 2.9gya with present day rotation period.g.) a land planet configuration at 2.9gya with the equivalent of 10m of water in soil and lakes. h.) a synchronously rotating version of a, f, and g (supported by recent work of [4] and older work of [5]) i.) a venus topography with a 310m ocean, but using present day insolation (1.9 x earth). j.) versions of most of the worlds above but with solar insolations >1.9 to explore more venus-like exoplanetary worlds around g-type stars. in these additional cases the planet still resides in the liquid water habitable zone. studies such as these should help astronomers better understand whether exoplanets found in the venus zone [6] are capable of hosting liquid water on their surfaces and whether significant resources should be directed at their characterization in the future. [1] way, m.j. et al. (2016) grl, 43, 8376 [2] way, m.j. et al. (2017) apjs, 231, 1[3] edwards, j.m., slingo, a. (1996) q. j. royal. met. soc. 122, 689[4] barnes, r. (2017) cel mech dyn ast, in press[5] dobrovolskis & ingersoll (1980), icarus, 41, 1[6] kane et al. (2013), apjl 794, 5 | modeling venus-like worlds through time and implications for the habitable zone |
uv stellar radiation can significantly impact planetary atmospheres through heating and photochemistry, even regulating production of potential biomarkers. m dwarfs emit the majority of their uv radiation in the form of emission lines, and the incident uv radiation on habitable-zone planets is significant owing to their small orbital radii. only recently have the uv spectral energy distributions (seds) of average m dwarfs been explored (e.g., the muscles treasury survey). emission lines tracing hot plasma in the stellar chromosphere and transition region dominate the far-uv spectra, even for optically inactive m dwarfs (i.e., those displaying hα absorption spectra). lyα (1216 å) is the strongest of the uv emission lines, but resonant scattering from the interstellar medium makes direct observations of the intrinsic lyα emission of even nearby stars challenging. i reconstruct the intrinsic lyα profiles using an mcmc technique and use them to estimate the extreme-uv sed.monitoring the long-term (years-to-decades) uv activity of m dwarfs will be important for assessing the potential habitability of short-period planets, but will only be feasible from the ground via optical proxies. therefore, i also quantify correlations between uv and optical emission lines of the muscles stars and other m dwarfs, for use when direct uv observations of m dwarf exoplanet host stars are not available. recent habitability studies of m dwarf exoplanets have sought to address the impact of frequent flaring and are just beginning to include the damaging impact of stellar energetic particles that are typically associated with large flares. working under the necessary assumption of solar-like particle production, i present a new technique for estimating >10 mev proton flux during far-uv flares, and analyze a sample of the flares observed in the muscles treasury survey. | optical-to-uv correlations and particle fluxes for m dwarf exoplanet host stars |
the synergy between kepler and the ground-based radial velocity (rv) surveys have made numerous discoveries of small and rocky exoplanets, opening the age of earth analogs. however, most (29/33) of the rv-detected exoplanets that are smaller than 3 earth radii do not have their masses constrained to better than 20% - limited by the current rv precision (1-2 m/s). our work improves the rv precision of the keck telescope, which is responsible for most of the mass measurements for small kepler exoplanets. we have discovered and verified, for the first time, two of the dominant terms in keck's rv systematic error budget: modeling errors (mostly in deconvolution) and telluric contamination. these two terms contribute 1 m/s and 0.6 m/s, respectively, to the rv error budget (rms in quadrature), and they create spurious signals at periods of one sidereal year and its harmonics with amplitudes of 0.2-1 m/s. left untreated, these errors can mimic the signals of earth-like or super-earth planets in the habitable zone. removing these errors will bring better precision to ten-year worth of keck data and better constraints on the masses and compositions of small kepler planets. as more precise rv instruments coming online, we need advanced data analysis tools to overcome issues like these in order to detect the earth twin (rv amplitude 8 cm/s). we are developing a new, open-source rv data analysis tool in python, which uses bayesian mcmc and gaussian processes, to fully exploit the hardware improvements brought by new instruments like minerva and nasa's wiyn/epds. | weighing rocky exoplanets with improved radial velocimetry |
observations of terrestrial exoplanet environments remain an important frontier in comparative planetology. studies of habitable zone terrestrial planets will set our own earth in a broader context. hot, post-runaway terrestrial exoplanets can provide insights into terrestrial planet evolution - and may reveal planetary processes that could mimic signs of life, such as photochemically-produced oxygen. while transmission spectroscopy observations of terrestrial planet atmospheres with jwst will be extremely challenging, they will afford our first chance to characterize the atmospheres of planets orbiting in the habitable zone of m dwarfs. however, due to the effects of refraction, clouds and hazes, jwst will likely sample the stratospheres of habitable zone terrestrial planets, and will not be able to observe the planetary surface or near-surface atmosphere. these limitations will hamper the search for signs of habitability and life, by precluding detection of water vapor in the deep atmosphere, and confining biosignature searches to gases that are prevalent in the stratosphere, such as evenly-mixed o2, or photochemical byproducts of biogenic gases. in contrast, direct imaging missions can potentially probe the entire atmospheric column and planetary surface, and can typically obtain broader wavelength coverage for habitable zone planets orbiting more sun-like stars, complementing the m dwarf planet observations favored by transmission spectroscopy. in this presentation we will show results from theoretical modeling of terrestrial exoplanet environments for habitable earth-like, early earth and highly-evolved hot terrestrial planets - with photochemistry and climates that are driven by host stars of different spectral types. we will also present simulated observations of these planets for both transmission (jwst) and direct imaging (luvoir-class) observations. these photometric measurements and spectra help us identify the most - and least - observable features of these planetary environments, and illuminate the strengths and limitations of each class of observation for future terrestrial planet characterization studies. | what we could learn from observations of terrestrial exoplanets |
what was the big deal behind the kepler news conference yesterday? its not just that the number of confirmed planets found by kepler has more than doubled (though thats certainly exciting news!). whats especially interesting is the way in which these new planets were confirmed.number of planet discoveries by year since 1995, including previous non-kepler discoveries (blue), previous kepler discoveries (light blue) and the newly validated kepler planets (orange). [nasa ames/w. stenzel; princeton university/t. morton]no need for follow-upbefore kepler, the way we confirmed planet candidates was with follow-up observations. the candidate could be validated either by directly imaging (which is rare) or obtaining a large number radial-velocity measurements of the wobble of the planets host star due to the planets orbit. but once kepler started producing planet candidates, these approaches to validation became less feasible. a lot of kepler candidates are small and orbit faint stars, making follow-up observations difficult or impossible.this problem is what inspired the development of whats known as probabilistic validation, an analysis technique that involves assessing the likelihood that the candidates signal is caused by various false-positive scenarios. using this technique allows astronomers to estimate the likelihood of a candidate signal being a true planet detection; if that likelihood is high enough, the planet candidate can be confirmed without the need for follow-up observations.a breakdown of the catalog of kepler objects of interest. just over half had previously been identified as false positives or confirmed as candidates. 1284 are newly validated, and another 455 have fpp of1090%. [morton et al. 2016]probabilistic validation has been used in the past to confirm individual planet candidates in kepler data, but now timothy morton (princeton university) and collaborators have taken this to a new level: they developed the first code thats designed to do fully automated batch processing of a large number of candidates.in a recently published study the results of which were announced yesterday the teamapplied their code to the entire catalog of 7,470 kepler objects of interest.new planets and false positivesthe teams code was able to successfully evaluate the total false-positive probability (fpp) for 7,056 of the objects of interest. of these, 428 objects previously identified as candidates were found to have fpp of more than 90%, suggesting that they are most likely false positives.periods and radii of candidate and confirmed planets in the kepler objects of interest catalog. blue circles have previously been identified as confirmed planets. candidates (orange) are shaded by false positive probability; more transparent means more likely to be a false positive. [morton et al. 2016]in contrast, 1,935 candidates were found to have fpp of less than 1%, and were therefore declared validated planets. of these confirmations, 1,284 were previously unconfirmed, more than doubling keplers previous catalog of 1,041 confirmed planets. morton and collaborators believe that 9 of these newly confirmed planets may fall within the habitable zone of their host stars.while the announcement of 1,284 newly confirmed planets is huge, the analysis presented in this study is the real news. the code used is publicly available and can be applied to any transiting exoplanet candidate. this means that this analysis technique can be used to find batches of exoplanets in data from the extended kepler mission (k2) or from the future tess and plato transit missions.citationtimothy d. morton et al 2016 apj 822 86. doi:10.3847/0004-637x/822/2/86 | a new way to confirm planet candidates |
the large uv-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 8-16 m range and a total bandpass spanning from the far-uv to the near-infrared. this observatory will enable revolutionary new studies in many areas of astronomy, including planetary science within and beyond our solar system. because luvoir is being considered for the next decadal survey, it must be capable of advancing our understanding of astronomical targets, including exoplanets, far beyond what will be achieved by the next two decades of observations from other space- or ground-based facilities. this means that the mission must move past planet detection, which is happening now with kepler and ground-based measurements and will continue with tess (transiting exoplanet survey satellite) and wfirst (wide field infrared survey telescope). it must also move beyond the chemical characterization of gas giants, which has begun with observations from spitzer, hubble, and ground-based telescopes and will greatly advances with the upcoming jwst (james webb space telescope) and wfirst coronagraph. therefore, one of luvoir's main science objectives will be to directly image rocky earth-sized planets in the habitable zones of other stars, measure their spectra, analyze the chemistry of their atmospheres, and obtain information about their surfaces. such observations will allow us to evaluate these worlds' habitability and potential for life. we will review the specific observational strategies needed for astrobiological assessments of exoplanetary environments, including the wavelength range and spectral resolution required for these habitability analyses and biosignature searches. further, we will discuss how the observational requirements to make measurements of "earthlike" worlds will allow high-quality observations of a wide variety of non-habitable exoplanets. the survey of the atmospheric composition of hundreds of worlds will also bring about a revolution in our understanding of planetary formation and evolution, and help place planets inside our solar system in a broader comparative planetology context. | the luvoir decadal mission concept |
given recent discoveries there is a very real potential for tidally-locked earth-like planets to exist orbiting m stars. to determine whether these planets may be habitable it is necessary to understand the nature of their atmospheres. in our investigation we simulate the evolution of present-day earth while placed in tidally-locked orbit (meaning the same side of the planet always faces the star) around an m dwarf star. we are particularly interested in the evolution of the planet's ozone layer and whether it will shield the planet, and therefore life, from harmful radiation.to accomplish the above objectives we use a state-of-the-art 3-d terrestrial model, the whole atmosphere community climate model (waccm), which fully couples chemistry and climate, and therefore allows self-consistent simulations of atmospheric constituents and their effects on a planet's climate, surface radiation and thus habitability. preliminary results show that this model is stable and that a tidally-locked earth is protected from harmful uv radiation produced by g stars. the next step shall be to adapt this model for an m star by including its uv and visible spectrum.this investigation will both provide an insight into the potential for habitable exoplanets and further define the nature of the habitable zones for m class stars. we will also be able to narrow the definition of the habitable zones around distant stars, which will help us identify these planets in the future. furthermore, this project will allow for a more thorough analysis of data from past and future exoplanet observing missions by defining the atmospheric composition of earth-like planets around a variety of types of stars. | assessing the chemistry of tidally locked earth-like planets around m-type stars using a 3d coupled chemistry-climate model (cesm/waccm) |
direct imaging plays a key role in the detection and characterization of exoplanets orbiting within its host star's habitable zone. many innovative ideas for starlight suppression and wavefront control have been proposed and developed over the past decade. however, several technological challenges still lie ahead to achieve the required contrast, including controlling the observatory pointing performance, fabricating occulting masks with tight optical tolerances, developing wavefront control algorithms, controlling stray light, advancing single photon detecting detectors, and integrated system-level issues. this paper explores how a lenslet array and pinhole mask may be implemented to further suppress uncorrected starlight that leaks through the occulting mask. an external occulter, or star shade, is simulated to demonstrate this concept, although this approach can be implemented for internal coronagraphs as well. we describe how to use simple relay optics to control the scene near the inner working angle and the level of the suppression expected. furthermore, if the lenslet array is the input to an integral field spectrograph, as planned for the wfirst mission, the spectral content of the exoplanet atmospheres can be obtained to determine if the observed planet is habitable and ultimately, if it is inhabited. | lenslet array to further suppress starlight for direct exoplanet detection |
the kepler mission was designed to detect transiting exoplanets and has succeeded in finding over 4000 candidates. these candidates include approximately 50 terrestrial-sized worlds near to the habitable zone of their gkm dwarf stars (shown in figure against the stellar temperature). however not all transit detections are created equal. false positives, such as background eclipsing binaries, can mimic the signal of a transiting planet. additionally, at kepler's detection limit noise, either from the star or from the detector, can create signals that also mimic a transiting planet. for the data release 25 kepler catalog we simulated these false alarms and determined how often known false alarms are called candidates. when this reliability information is combined with our studies of catalog completeness, this catalog can be used to understand the occurrence rate of exoplanets, even for the small, temperate planet candidates found by kepler. i will discuss the automated methods we used to create and characterize this latest catalog, highlighting how we balanced the completeness and reliability of the long period candidates. while kepler has been very successful at detecting transiting terrestrial-sized exoplanets, many of these detections are around stars that are too dim for successful follow-up work. future missions will pick up where kepler left off and find small planets around some of the brightest and smallest stars. | kepler's final survey catalog |
over 3500 extrasolar planets have been discovered recently, and a critical question is which types of these exoplanets are potentially habitable. a variety of previous work is concentrated on atmospheric dynamics and its effects on planetary climates. in this study, we expand the research by examining ocean dynamical regimes on exoplanets. using a one-layer shallow water ocean model, we examine how planetary rotation rate, wind stress, fluid viscosity, ocean depth, ocean basin structure (closed or open in zonal direction) and surface gravity influence the pattern and strength of the wind-driven ocean circulations on exoplanets. our simulations demonstrate that in closed basins, planetary rotation rate and its variation in meridional direction (i.e., the beta effect) fundamentally determine the westward intensification and ocean pattern, and changes of other factors contribute to enhancing or weakening the ocean circulation pattern. for open ocean basins (with no west and east barriers, like the antarctic circumpolar current region on our earth), the ocean pattern is characterized by laminar flow and is more stable. we further find that the model results can be well reproduced by analytic solutions when the nonlinear advection terms are small. this work improves our understanding of exoplanetary oceanography and provides important implications for studying the climates and habitability of exoplanets with oceans. | wind-driven ocean circulations on exoplanets |
habex is one of four candidate flagship missions being studied in detail by nasa, to be submitted for consideration to the 2020 decadal survey in astronomy and astrophysics for possible launch in the 2030s. it will be optimized for direct imaging and spectroscopy of potentially habitable exoplanets, and will also enable a wide range of general astrophysics science. habex aims to fully characterize planetary systems around nearby solar-type stars for the first time, including rocky planets, possible water worlds, gas giants, ice giants, and faint circumstellar debris disks. in particular, it will explore our nearest neighbors and search for signs of habitability and biosignatures in the atmospheres of rocky planets in the habitable zones of their parent stars. such high spatial resolution, high contrast observations require a large (roughly greater than 3.5m), stable, and diffraction-limited optical space telescope. such a telescope also opens up unique capabilities for studying the formation and evolution of stars and galaxies. we present some preliminary science objectives identified for habex by our science and technology definition team (stdt), together with a first look at the key challenges and design trades ahead. | the habitable exoplanet (habex) imaging mission: preliminary science drivers and technical requirements |
m-dwarf stars are excellent targets for planet searches because the signal of an orbiting planet is relatively larger (and therefore easier to detect!) around small, dim m dwarfs, compared to sun-like stars. but are there better or worse stars to target within this category when searching for habitable, earth-like planets?confusing the signalradial velocity campaigns search for planets by looking for signatures in a stars spectra that indicate the star is wobbling due to the gravitational pull of an orbiting planet. unfortunately, stellar activity can mimic the signal of an orbiting planet in a stars spectrum something that is particularly problematic for m dwarfs, which can remain magnetically active for billions of years. to successfully detect planets that orbit in their stars habitable zones, we have to account for this problem.in a recent study led by elisabeth newton (harvard-smithsonian center for astrophysics), the authors use literature measurements to examine the rotation periods for main-sequence, m-type stars. they focus on three factors that are important for detecting and characterizing habitable planets around m dwarfs:whether the habitable-zone orbital periods coincide with the stellar rotationfalse planet detections caused by stellar activity often appear as a planet with an orbital period thats a multiple of the stellar rotation period. if a stars rotation period coincides with the range of orbital periods corresponding to its habitable zone, its therefore possible to obtain false detections of habitable planets.how long stellar activity and rapid rotation last in the starall stars become less magnetically active and rotate more slowly as they age, but the rate of this decay depends on their mass: lower-mass stars stay magnetically active for longer and take longer to spin down.whether detailed atmospheric characterization will be possibleits ideal to be able to follow up on potentially habitable exoplanets, and search for biosignatures such as oxygen in the planetary atmosphere. this type of detection will only be feasible for low-mass dwarfs, however, due to the relative size of the star and the planet.an ideal rangestellar rotation period as a function of stellar mass. the blue shaded region shows the habitable zone as a function of stellar mass. for m dwarfs between ~0.25 and ~0.5 solar mass, the habitable-zone period overlaps with the stellar rotation period. [newton et al. 2016]newton and collaborators find that stars in the mass range of 0.25 to 0.5 solar mass (stellar class m1v-m4v) are non-ideal targets, because their stellar rotation periods (or a multiple thereof) coincide with the orbital periods of their habitable zones. in addition, atmospheric characterization will only be feasible in the near future for stars with mass less than ~0.25 solar mass.on the other hand, dwarfs with mass less than ~0.1 solar masses (stellar classes later than m6v) will retain their stellar activity and faster rotation rates throughout most of their lifetimes, making them non-ideal targets as well.when searching for habitable exoplanets, the best targets are therefore the mid m dwarfs in the mass range of 0.1 to 0.25 solar mass (stellar class m4v-m6v). building a sample focused on these stars will reduce the likelihood that planets found in the stars habitable zones are false detections. this will hopefully produce a catalog of potentially habitable exoplanets that we can eventually follow up with atmospheric observations.citationelisabeth r. newton et al 2016 apj 821 l19. doi:10.3847/2041-8205/821/1/l19 | choosing stars to search for habitable planets |
direct imaging of earth-like extrasolar planets in the habitable zone and the search for possible biological signatures are among the key scientific objectives in the modern astronomy. stellar coronagraph such as achromatic interfero coronagraph (aic) with a small inner working angle has limited possibilities to detect and characterize planets around nearby stars due to the star leakage effect caused by incomplete suppression of the star of finite angular size. we report on an improved instrument for direct imaging of exoplanets and the study of stellar environment - common-path achromatic interfero-coronagraph with variable rotational shear (common-path achromatic rotation-shearing coronagraph, cp-arc) - a common path implementation of rotation shearing interferometer. we detail cp-arc approach and discuss its optical configuration, laboratory prototype and experimental results. | achromatic interfero-coronagraph with variable rotational shear in laboratory experiments |
we used california planet search ca ii h and k core emission measurements to identify and characterize chromospheric activity cycles in a sample of main-sequence fgk stars. about a dozen of these with existing rosat archival data were targeted with swift to obtain a current epoch x-ray flux. we find that coronal variability by a factor of several is common on decade-long timescales (we attempt to link to the chromospheric cycle phase) but can also occur on short timescales between swift visits to a given target, presumably related to stellar rotation and coronal inhomogeneity or to small flares.additionally, we present new swift monitoring observations of two m dwarfs with known exoplanets: gj 15a and gj 674. gj 15a b is around 5.3 earth masses with an 11.4 day orbital period, while gj 674 is around 11.1 earth masses with a 4.7 day orbital period. gj 15a was observed several times in late 2014 and then monitored at approximately weekly intervals for several months in early 2016, for a total exposure of 18 ks. gj 674 was monitored at approximately weekly intervals for most of 2016, for a total exposure of 40 ks. we provide light curves and hardness ratios for both sources, and also compare to earlier archival x-ray data. both sources show significant x-ray variability, including between consecutive observations. we quantify the energy distribution for coronal flaring, and compare to optical results for m dwarfs from kepler. finally, we discuss the implications of m dwarf coronal activity for exoplanets orbiting within the nominal habitable zone. | swift x-ray monitoring of stellar coronal variability |
the habitable exoplanet imager is one of four flagship missions that nasa is studying in advance of the 2020 decadal survey. the primary goal of habex is to directly image and characterize rocky planets in the habitable zones of sun-like stars. | habex: finding and characterizing habitable exoplanets with a potential future flagship astrophysics mission |
the discovery of kepler 452b is a milestone in searching for habitable exoplanets. while it was suggested that kepler 452b is the first earth-like exoplanet discovered in the habitable zone of a sun-like star, its climate states and habitability require quantitative studies. using a three-dimensional fully coupled atmosphere-ocean climate model, we perform simulations to demonstrate kepler 452b's climates for different co2 levels. our simulations show that kepler 452b is likely a habitable exoplanet if co2 concentrations in its atmosphere are comparable or lower than that in the earth atmosphere. however, our simulations also suggest that kepler 452b can readily fall into the moist greenhouse state and becomes uninhabitable in the absence of silicate weathering. we will also address whether kepler 452b can recover from the moist greenhouse state and whether the planet remains its water inventory after 6.5 billion years of life time. | climate and habitability of kepler 452b |
the discovery of short-period planets with masses and radii between earth and neptune was one of the biggest surprises in the brief history of exoplanet science. from the kepler mission, we now know that these “super-earths” or "sub-neptunes" orbit at least 40% of stars, likely representing the most common outcome of planet formation. despite this ubiquity, we know little about their typical compositions and formation histories. spectroscopic transit observations combined with powerful atmospheric retrieval tools can shed new light on these mysterious worlds. in this talk, we will present the main results from our 124-orbit hubble space telescope survey to reveal the chemical diversity and formation histories of super-earths. this unprecedented hst survey provides the first comprehensive look at this intriguing new class of planets ranging from 1 neptune mass and temperatures close to 2000k to a 1 earth mass planet near the habitable zone of its host star. | a large hubble space telescope survey of low-mass exoplanets |
the liquid water habitable zone (hz) describes the orbital distance at which a terrestrial planet can maintain above-freezing conditions through regulation by the carbonate-silicate cycle. calculations with one-dimensional climate models predict that the inner edge of the hz is limited by water loss through a runaway greenhouse, while the outer edge of the hz is bounded by the maximum greenhouse effect of carbon dioxide. this classic picture of the hz continues to guide interpretation of exoplanet discoveries; however, recent calculations have shown that terrestrial planets near the outer edge of the hz may exhibit other behaviors that affect their habitability. here i discuss results from a hierarchy of climate models to understand the stellar environments most likely to support a habitable planet. i present energy balance climate model calculations showing the conditions under which planets in the outer regions of the habitable zone should oscillate between long, globally glaciated states and shorter periods of climatic warmth, known as `limit cycles.' such conditions would be inimical to the development of complex land life, including intelligent life. limit cycles may also provide an explanation for fluvial features on early mars, although this requires additional greenhouse warming by hydrogen. these calculations show that the net volcanic outgassing rate and the propensity for plant life to sequester carbon dioxide are critical factors that determine the susceptibility of a planet to limit cycling. i argue that planets orbiting mid g- to mid k-type stars offer more opportunity for supporting advanced life than do planets around f-type stars or m-type stars. | limit cycles at the outer edge of the habitable zone |
in the search for habitable exoplanets, astronomers' primary criterion has historically been that the planet's equilibrium temperature be suitable for liquid water. equilibrium temperature is often determined assuming a circular orbit and, therefore, a constant star-planet separation, especially for low-mass transiting exoplanets. using photometric data from the first kepler mission, we analyze the transit light curves of kepler 186, an exoplanetary system located approximately 150pc from earth. in this poster, we report new lower limits on the eccentricities of the system found using the astrodensity profiling method and discuss how those values effect habitabilty. we also report other orbital, stellar, and planetary properties, which are consistent with, though slightly more precise than, the values reported in quintana et al, 2014. we assert that, with an eccentricity of 0.092, a semimajor axis of 0.35 au, and a radius of 1.06 earth radii, kepler 186f is an earth-sized exoplanet that spends its entire orbit in the habitable zone of its star. | home sweet home?: determining habitability from the eccentricities of kepler-186 |
the field of exoplanets has rapidly expanded from the exclusivity of exoplanet detection to include exoplanet characterization. a key step towards this characterization is the de- termination of which planets occupy the habitable zone (hz) of their host stars. as the kepler data continues to be processed, the orbital period sensitivity is increasing and there are now numerous exoplanets known to occupy the hz of their host stars. in this talk i will describe the properties of the hz, the dependence on stellar and planetary parameters, and the current state of exoplanet detections in the hz. along the way i will describe some common misconceptions regarding the habitable zone and detail caveats to the model. i will conclude with a pathway for testing the habitable zone model and answering the question: what is the purpose of the habitable zone? | definitions and caveats of the habitable zone |
editors note:in these last two weeks of 2015, well be looking at a few selections from among the most-downloaded paperspublished in aas journals this year. the usual posting schedule will resume after the aas winter meeting.discovery and validation of kepler-452b: a 1.6 r super earth exoplanet in the habitable zone of a g2 starpublished july2015main takeaway:a phase-folded light curve showing the transit of kepler-452b. its transit lasts 10.5 hours, and its period is 385 days. [jenkins et al. 2015]a team led by jon jenkins (nasa ames research center) announced the discovery and confirmation of kepler-452b, an exoplanet only 60% larger than earth and located in the habitable zone of its g2 star. this planet orbits its star at a distance of just over 1 au, taking 385 days to complete an orbit. kepler-452b also stands a good chance of being rocky, according to estimates.why its interesting:kepler-452b is the first near-earth-sized planet to be found in the habitable zone of a sun-like star making this the closest analog to the earth-sun system found in the kepler dataset so far.about the history of the system (and the future of ours?):the authors estimate that the system is ~6 billion years old, and that kepler-452b has been in the habitable zone of its star throughout its lifetime a substantially longer time than earth has been around and habitable! kepler-452bs host star, in addition to being 1.5 billion years older than the sun, is roughly 10% larger. this system might therefore provide a glimpse of what earths environment may be like in the future, as the sun slowly expands on its way to becoming a red giant.citationjon m. jenkins et al 2015 aj 150 56. doi:10.1088/0004-6256/150/2/56 | selections from 2015: earth-sized planet found in star's habitable zone |
with about 2000 exoplanets discovered within a large range of different configurations of distance from the star, size, mass, and atmospheric conditions, the concept of habitability cannot rely only on the stellar effective temperature anymore. in addition to the natural evolution of habitability with the intrinsic stellar parameters, tidal, magnetic, and atmospheric interactions are believed to have strong impact on the relative position of the planets inside the so-called habitable zone. moreover, the notion of habitability itself strongly depends on the definition we give to the term ``habitable''. the aim of this talk is to provide a global and up-to-date overview of the work done during the last few years about the description and the modelling of the habitability, and to present the physical processes currently includes in this description. | host's stars and habitability |
the discovery of planets with masses and radii intermediate between earth and neptune was one of the biggest surprises in the brief history of exoplanet science. these "super-earths" are an order of magnitude more abundant than close-in giant planets. despite this ubiquity, we know little about their typical compositions and formation histories. spectroscopic transit observations can shed new light on these mysterious worlds by probing their atmospheric compositions. in this talk, we will give an overview of our ongoing 124-orbit (200-hour) hubble space telescope program to reveal the chemical diversity and formation histories of super-earths. this unprecedented survey will provide the first comprehensive look at this intriguing new class of planets ranging from 1 neptune mass and temperatures close to 2000k to a 1 earth mass planet near the habitable zone of its host star. we will discuss the scope of the program, demonstrate observational techniques to observe extremely bright exoplanet targets with hst wfc3 and stis, and present early results. | exploring the diversity of super-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 |
the likelihood of finding an earth-like planet in the habitable zone of an m dwarf in the near future is very high. in order to characterize such a planet's habitability, we need to understand how much ultraviolet (uv) radiation the planet is receiving from its host star. uv light from the host star influences a planet's atmospheric photochemistry and will affect our interpretations of measured exoplanetary atmospheric compositions from future missions like jwst and the extremely large ground-based telescopes. time resolved uv data for a large number of stars can provide more detailed boundary conditions for atmospheric modeling and information on the activity behavior of low-mass stars. the galaxy evolution explorer (galex) provides time resolved data in the near- ultraviolet (nuv) band (1771 - 2831 å). on average, there are 4 uv observations per m dwarf in our population of 436 m dwarfs within 25 pc of earth. the galex mission has multiple surveys, which covered different sized areas of the sky. at the final data release, the all sky survey (ais) covered 2/3 of the sky and accounts for 58% of our 2595 measurements. the deep imaging survey (dis), medium imaging survey (mis), guest investigator survey (gii), and nearby galaxy survey (ngs) contribute the remaining data. from the nuv galex data we find an increase in variability among later m dwarfs within the m0 - m4 range. m0 stars vary on average by 9% around their mean flux, while m4 stars vary by 31% around their mean flux. | measuring the ultraviolet variability of m dwarfs with galex |
the search for habitable exoplanets is currently focused on planets orbiting m-dwarf stars, due to the close proximity of the habitable zone to the star. however, the traditional habitability definition does not account for the physical space environment near the planets, which can be extreme at close-in orbits, and can lead to erosion of te planetary atmosphere. in order to sustain their atmosphers, m-dwarf planets need to have either an intrinsic magnetic field, or a thick atmosphere. here we present a set of numerical magnetohydrodynamic simulations of the interaction of an earth-like magnetized planet and a venus-like non-magnetized planet with the stellar wind of m-dwarf star. we study space physics aspects of these interactions and their implications for planet habitability | space physics of close-in exoplanets and its implications for planet habitability |
the discovery of short-period planets with masses and radii between earth and neptune was one of the biggest surprises in the brief history of exoplanet science. from the kepler mission, we know that these "super-earths" or "sub-neptunes" orbit at least 40% of stars, likely representing the most common outcome of planet formation. despite this ubiquity, we know little about their typical compositions and formation histories. in this talk, we will shed new light on these worlds by presenting the multiple the main results from our 124-orbit hst transit spectroscopy survey to probe the chemical compositions of low-mass exoplanets. we will report on multiple molecular detections. our unprecedented hst survey provides the first comprehensive look at this intriguing new class of planets by covering seven planets ranging from 1 neptune mass and temperatures close to 2000k to a 1 earth-mass planet near the habitable zone of its host star. | a large hubble space telescope survey of low-mass exoplanets |
galactic gravitational microlensing is a very e!cient technique to detect brown dwarfs and extrasolar planets at large orbital distances from their stars, and down to earth-mass planets. the exoplanets discovered are beyond the snow line and typically close to the habitable zone of their host stars. i will present the specificity of the microlensing method to detect exoplanets, discuss the detections made so far, and present the different methods to constrain the mass of the lens hosting a planet. finally, i will describe how can interferometry lead to an independent mass determining through the measurement of the lens einstein radius. | exoplanets mass measurement using gravitational microlensing |
the planet occurrence rate has been found to increase with decreasing stellar mass (later spectral types) in the original kepler field, and one out of four m dwarfs are expected to host earth-sized planets within their habitable zones. m dwarf systems are, therefore, our most promising targets in the search for exoplanets. yet the identification and characterization of m dwarfs in the kepler field was accomplished using photometry alone and unfortunately this method provides large uncertainties for late-type stars. notably absent from planet occurrence calculations are single planet mid-type m dwarfs (~m2-m6). in order to make an accurate calculation of the planet occurrence rate around mid-type m dwarfs, we need to constrain stellar radii and masses which depend on other stellar parameters (e.g. temperature and metallicity). we have identified 559 probable mid-type m dwarfs using photometric color selection criteria and have started to gather spectra of these objects in order to better constrain stellar properties and refine planet occurrence rates for this population. here we outline the methods we are using for stellar classification and characterization and present some results from our initial data. | characterization of mid-type m dwarfs in the kepler field |
habitable zones are a hot topic in exoplanet studies: where, around a given star, could a planet exist that supports life? but if you scale this up, you get a much less common question: which type of galaxy is most likely to host complex life in the universe? a team of researchers from the uk believes it has the answer.criteria for habitabilityled by pratika dayal of the university of durham, the authors of this study set out to estimate the habitability of a large population of galaxies. the first step in this process is to determine what elements contribute to a galaxys habitability. the authors note three primary factors:total number of starsmore stars means more planets!metallicity of the starsplanets are more likely to form in stellar vicinities with higher metallicities, since planet formation requires elements heavier than iron.likelihood of type ii supernovae nearbyplanets that are located out of range of supernovae have a higher probability of being habitable, since a major dose of cosmic radiation is likely to cause mass extinctions or delay evolution of complex life. galaxies supernova rates can be estimated from their star formation rates (the two are connected via the initial mass function).hospitable cosmic giantslower panel: the number of earth-like habitable planets (given by the color bar, which shows the log ratio relative to the milky way) increases in galaxies with larger stellar mass and lower star formation rates. upper panel: the larger stellar-mass galaxies tend to be elliptical (blue line) rather than spiral (red line). click for larger view. [dayal et al. 2015]interestingly, these three conditions have previously been shown to be linked via something termed the fundamental metallicity relation, which relates the total stellar masses, metallicities, and star formation rates of galaxies. by using this relation, the authors were able to create predictions for the number of habitable planets in more than 100,000 galaxies in the local universe (cataloged by the sloan digital sky survey).based on these predictions, the authors find that the galaxies likely to host the largest number of habitable planets are those that have a mass greater than twice that of the milky way and star formation rates less than a tenth of that of the milky way.these galaxies tend to be giant elliptical galaxies, rather than compact spirals like our own galaxy. the authors calculate that the most hospitable galaxies can host up to 10,000 times as many earth-like planets and 1,000,000 times as many gas-giants (which might have habitable moons) as the milky way!citationpratika dayal et al.2015 apj 810 l2 doi:10.1088/2041-8205/810/1/l2 | which galaxies are the most habitable? |
m-dwarf stars are prime targets in the search for habitable exoplanets because the stars are smaller and the habitable zone is quite close to the star. surveys have revealed a considerable number of tightly packed planetary systems around small stars, and this raises the question of how closely planets can be packed together and stay stable for billions of years. using numerical simulations, we have investigated the stability of hypothetical systems comprised of several earth-mass planets around an m-dwarf star, where the planets' orbits are all evenly spaced in mutual hill radii. we reproduce the obvious: that, in general, the more tightly packed a system is the faster it will go unstable. however, we see structure superimposed on this general trend that can cause a system's lifetime to differ by several orders of magnitude over a small difference in planet spacing. we will discuss implications for the maximum number earth-mass planets that can fit in an m-dwarfs' habitable zone. | stability of evenly spaced, tightly packed systems of earth-massed planets around m-dwarfs |
although observations of exoplanetary observations remain rather limited, our inner solar system continues to be a useful springboard for understanding exoplanetary habitability. indeed, the habitable zone (hz), which is a navigational tool for finding potentially habitable exoplanets, was partially designed from our knowledge of earth, mars, and venus. here, i discuss how these solar system links have updated the hz and continued to improve our understanding of planetary habitability both inside and outside our solar system. the notion that early mars may have been a habitable planet with a dense co2-h2 atmosphere has led to the development of a wider volcanic hydrogen hz with more potentially habitable planets (e.g. trappist-1h)1. also, spectral class greatly influences habitability. for instance, high amounts of methane in dense co2-ch4 atmospheres near the outer edge of hotter ( a - mid-k) stars may suggest inhabitance2, which is consistent with recent studies of the early earth3. i then assess whether abiotic processes (e.g. serpentinization, impacts, volcanism) can also produce similar co2-ch4 atmospheres and whether we can distinguish such false positives. in contrast, m-star hz outer edge planets with such co2-ch4 atmospheres are likely to be frozen worlds instead. plus, the possibility that both venus and mars may have been habitable illustrates why the pre-main-sequence hz is crucial for estimating planetary water inventories and inferring whether planets located in the hz today are truly habitable or not4. finally, i briefly discuss how rotation rate impacts the habitability of ocean worlds with water inventories much larger than earth's5. references: 1. ramirez, r.m., kaltenegger, l., 2017. a volcanic hydrogen habitable zone. the astrophysical journal letters, 837, 1 2. ramirez, r.m. and kaltenegger, l. 2018. a methane extension to the classical habitable zone. apj 858, 2 3. krissansen-totton, joshua, stephanie olson, and david c. catling. "disequilibrium biosignatures over earth history and implications for detecting exoplanet life." science advances 4.1 (2018): eaao5747. 4. ramirez, r.m., kaltenegger, l., 2014. habitable zones of pre-main-sequence stars. apjl, 797, 2, l25 5. ramirez, r.m. and levi, a. 2018. the ice cap zone: a unique habitable zone for ocean worlds. mnras, 477, 4, 4627- 4640 | linking the habitable zone to solar system and exoplanetary habitability |
habitable-zone rocky planets orbit nearly all stars; however, stellar flares make detecting these planets and discovering their actual habitability challenging. although kepler measured flare rates for various spectral-types around distant stars, the flare rates and intensities of nearby stars available to planet searches and follow-up remain poorly characterized. high-cadence, long-timescale photometry of such stars will provide the intensity and frequency of flares incident upon nearby hz planets. at the same time, optical counterparts to cme-exoplanet-magnetosphere searches in the radio, and potentially-reduced flare interference for radial-velocity planet searches are obtained. the evryflare project employs the ctio-based evryscope, a combination of twenty-four telescopes, together giving instantaneous sky coverage of 8000 square degrees. solar-type and red dwarf stars are selected by color and searched with an automated flare detector. we are currently sensitive to flares down to about 10 milli-magnitudes at g' 12 and about 0.2 of a magnitude at g' 15. with 2-minute cadence and a projected 5-year timeline with 1.5 years already recorded, we are precisely characterizing the flare rates and intensities of bright, nearby stars. with this information, we provide insight into the frequency and relative insolation incident upon hz planets discovered orbiting nearby stars, as well as provide optical counterparts for radio planetary magnetosphere searches. | evryflare: flare rates and intensities for every 10 < g' < 15 solar-type and red dwarf star in the southern sky |
it is known that the universe also contain many other planetary systems which are different from our solar system in terms of host star, number and natures of orbiting planets. the present paper aims at reviewing works done for observing exoplanets. for that purpose, detection technologies and methods are specified first. then, different possibilities of exoplanet characterization are presented. finally, progress of the search for habitable exoplanets is discussed. though earth is up to now the perfect planet ever known where life is possible, humanity does not lose hope and continues to invest to build more efficient exoplanet detection instruments. | progress in the observation of exoplanets |
planetary transits and ocillations (plato) is the third european space agency (esa) medium class mission in esa's cosmic vision programme due for launch in 2026. plato will carry out high precision un-interrupted photometric monitoring in the visible band of large samples of bright solar-type stars. the primary mission goal is to detect and characterise terrestrial exoplanets and their systems with emphasis on planets orbiting in the habitable zone, this will be achieved using light curves to detect planetary transits. plato uses a novel multi- instrument concept consisting of 26 small wide field cameras the 26 cameras are made up of a telescope optical unit, four teledyne e2v ccd270s mounted on a focal plane array and connected to a set of front end electronics (fee) which provide ccd control and readout. there are 2 fast cameras with high read-out cadence (2.5 s) for magnitude ~ 4-8 stars, being developed by the german aerospace centre and 24 normal (n) cameras with a cadence of 25 s to monitor stars with a magnitude greater than 8. the n-fees are being developed at university college london's mullard space science laboratory (mssl) and will be characterised along with the associated ccds. the ccds and n-fees will undergo rigorous on-ground characterisation and the performance of the ccds will continue to be monitored in-orbit. this paper discusses the initial development of the experimental arrangement, test procedures and current status of the n-fee. the parameters explored will include gain, quantum efficiency, pixel response non-uniformity, dark current and charge transfer inefficiency (cti). the current in-orbit characterisation plan is also discussed which will enable the performance of the ccds and their associated n-fee to be monitored during the mission, this will include measurements of cti giving an indication of the impact of radiation damage in the ccds. | on-ground and in-orbit characterisation plan for the plato ccd normal cameras |
future extremely large telescopes, equipped with high-contrast instruments targeting very small inner working angle, will provide the requisite resolution for detecting exoplanets in the habitable zone around m-stars. however, the elt segmented pupil shape is unfavourable to high-contrast imaging. in this context, the speed project aims to develop and test solutions for high contrast with unfriendly apertures. speed will combine a piaacmc coronagraph and two deformable mirrors for the wavefront shaping. in this paper, we describe an end-to-end model of speed, including the fresnel wavefront propagation, the piaacmc implementation and the dark hole algorithm, and present a statistical analysis of the predicted performance. | an end-to-end fresnel propagation model for speed: piaacmc implementation and performance |
this presentation will give an overview of the exoplanetary and planetary observing capabilities of the large uv-optical-infrared (luvoir) surveyor. luvoir is one of four large mission concepts for which the nasa astrophysics division has commissioned studies by science and technology definition teams (stdts) drawn from the astronomical community, in advance of the next astrophysics decadal survey. luvoir is a general-purpose space-based observatory with a wavelength range spanning from the far-uv to the near-infrared, and will support a broad range of astrophysics, exoplanet and solar system studies. luvoir will operate at the sun-earth l2 point, and will be designed for extreme stability to support unprecedented spatial resolution and coronagraphy. it is intended to be a long-lifetime facility that is both serviceable, upgradable, and primarily driven by guest observer science programs.one of the main science objectives for luvoir will be to directly image rocky-sized planets in the habitable zones of stars out to 20 pc, measure their spectra, analyze the chemistry of their atmospheres, and obtain top-level information about their surfaces. such observations will allow us to evaluate the habitability of these worlds, and search for potential signs of life in their spectra. luvoir will also be capable of ultra-high spatial resolution imaging of solar system bodies, and simultaneous spectroscopy between 300 nm and 2 microns. we will review the specific observational strategies needed for astrobiological assessments of both exoplanetary and solar system environments, including the wavelength range and spectral resolution required for these habitability analyses and biosignature searches, and we will provide an overview of the luvoir instrument capabilities and planned survey strategy to achieve these goals. we will also describe the wide range of additional exoplanetary and planetary science that luvoir will accomplish, including high-quality spectroscopic analysis of hundreds of directly imaged neptune- and jupiter-class objects, transit spectroscopy of m-earths and other transiting planets across the visible and near-ir, and high-precision time-domain astronomy of every planet in the solar system. | exoplanet and solar system science with the luvoir mission |
potential solar tides in an ancient venusian ocean are simulated using a dedicated numerical tidal model. a series of simulations with ocean depths varying between 330-4500m and rotational periods ranging from -243 to 64 earth days were used to calculate tidal dissipation rates and the resulting tidal torque and associated spin down of venus' rotation rate. the results show that tidal dissipation rates on venus could have varied over 3 orders of magnitude depending on rotational period and ocean depth, with the most energetic simulations dissipating nearly as much tidal energy as the solar tide does in earth's oceans today. this occurs at all depth configurations when the rotation period is close to one earth day. the associated tidal torque is large and of the same order of magnitude as today's total tidal torque on earth and an order of magnitude below the atmospheric torque reported for present-day venus. consequently, an ocean tide on ancient venus, albeit probably short-lived in geological terms, could have had significant effects on the rotational history of the planet if its rotation rate was faster than today. in fact it could have changed the rotational period by several days per million years. these calculations have important implications for the rotational periods of exoplanetary worlds and the location of the inner edge of the liquid water habitable zone. | ocean tides and rotation rates: a venusian application |
evidence from the solar system suggests that, unlike venus and mars, the presence of a strong magnetic dipole moment on earth has helped maintain liquid water on its surface. therefore, planetary magnetism could have a significant effect on the long-term maintenance of atmosphere and liquid water on rocky exoplanets. we use olson & christensen's (2006) model to estimate magnetic dipole moments of rocky exoplanets with radii rp ≤ 1.23 rearth. even when modelling maximum magnetic dipole moments, only kepler-186 f has a magnetic dipole moment larger than the earth's, while approximately half of rocky exoplanets detected in the circumstellar habitable zone have a negligible magnetic dipole moment. this suggests that planetary magnetism is an important factor when prioritizing observations of potentially habitable planets. | planetary magnetism as a parameter in exoplanet habitability |
a rigorous defi nition of the habitable zone and its dependence on planetary properties is part of the search for habitable exoplanets. in this work, we use the general circulation model exocam to determine how the inner edge of the habitable zone of tidally locked planets orbiting m dwarf stars depends on planetary radius, surface gravity, and surface pressure. we fi nd that the inner edge of the habitable zone for more massive planets occurs at higher stellar irradiation, as found in previous 1d simulations. we also determine the relative effects of varying planetary radius and surface gravity. increasing the planetary radius leads to a lower planetary albedo and warmer climate, pushing the inner edge of the habitable zone to lower stellar irradiation. this results from a change in circulation regime that leads to the disruption of the thick, refl ective cloud deck around the substellar point. increasing gravity increases the outgoing longwave radiation, which moves the inner edge of the habitable zone to higher stellar irradiation. this is because the column mass of water vapor decreases with increasing gravity, leading to a reduction in the greenhouse effect. the effect of gravity on the outgoing longwave radiation is stronger than the effect of radius on the planetary albedo, so that increasing gravity and radius together causes the inner edge of the habitable zone to move to higher stellar irradiation. our results show that the inner edge of the habitable zone for more massive terrestrial planets occurs at a larger stellar irradiation. with the resulting stellar irradiation, we give the estimated orbital periods for planets at inner edges which may contribute to the observation of habitable worlds. | effects of radius and gravity on the inner edge of the habitable zone |
direct imaging of exoplanets will increasingly become a more popular method of exoplanet detection and characterization as larger space telescopes equipped with better technology and more ambitious scientific objectives are launched. among other scientific objectives, nasa's large ultraviolet/optical/infrared surveyor (luvoir) aims to detect and characterize exoplanets within 50 parsecs of the sun, making the goal of direct exoplanet detection a reality. this paper describes simulations that predict that luvoir will detect 54 earth-like exoplanets within two years of a dedicated campaign. the simulation's detection criteria require that the exoplanet be visible within the working angle of the focal plane, be within the habitable zone, produce a signal-to-noise ratio greater than seven and a contrast ratio greater than 10-10 with respect to the parent star. we find that although it is possible to detect exoplanets around m dwarfs, they are not ideal targets due to their low brightness and luminosity. although it could be included in future work, we have not produced a specific list of stars that luvoir could observe. our approach determines the characteristics of stars that produce the highest completeness, which could lead to such a list in the future. | simulating the earth-like exoplanet yield of the nasa luvoir 'a' architecture direct-imaging mission |
since the discovery of the first exoplanet more than two decades ago, the field of exoplanets has drastically expanded. this expansion has been driven in large part due to advances in instrumental capabilities, increasing our sensitivity to detecting and characterizing these exoplanetary worlds. in this dissertation talk, i discuss the development of new high-precision ground-based instrumentation for both transit photometry and radial velocimetry (rv). first, i discuss the use of beam-shaping diffusers to enable hitherto unachievable photometric precisions from the ground. beam-shaping diffusers are micro-structured optical components capable of molding the image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, and telescope-induced variable aberrations seen in defocusing. i discuss my efforts in commissioning an optical diffuser on the arc 3.5m telescope at apache point observatory demonstrating 62ppm precision in 30 minute bins—some of the highest photometric precisions from the ground. being inexpensive, beam-shaping diffusers can be easily adapted for use on telescopes large and small for precision photometry applications. second, i discuss the design and use of two next generation fiber-fed ultra-stabilized rv spectrographs designed from the bottom-up to carry out dedicated surveys to discover and characterize rocky terrestrial worlds. the habitable-zone planet finder (hpf) is a next generation high resolution (r~55,000) near-infrared (nir) spectrograph installed on the 10m hobby-eberly telescope (het) in late 2017. neid is the next generation high-resolution (r~100,000) optical spectrograph to be installed at the 3.5m wiyn telescope at kitt peak in early 2019. i will discuss my efforts on the design and build of various subsystems for hpf and neid, including the hpf and neid environmental control systems. finally, i will discuss on-sky commissioning and early science results from hpf which has already demonstrated 1.53m/s precision in the nir on the nearby bright m-dwarf gj 699 over 3 months. | extreme precision photometry and radial velocimetry from the ground |
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