GESTIÓN DE RESIDUOS ÍNDICE
PREVISTAS PARA EL ALMACENAMIENTO,
331.01 — Dying to Live: Post-Main Sequence Hab- itability
Thea Kozakis1; Lisa Kaltenegger1
1 Carl Sagan Institute, Cornell Univeristy (Ithaca, New York, United States)
During the post-main sequence phase of stellar evo- lution the orbital distance of the habitable zone, which allows for liquid surface water on terres- trial planets, moves out past the system’s original frost line, providing an opportunity for outer plan- etary system surface habitability. We use a 1D cou- pled climate/photochemistry code to study the im- pact of the stellar environment on the planetary at- mospheres of Earth-like planets/moons throughout its time in the post-main sequence habitable zone. We also explore the ground UV environments of such planets/moons and compare them to Earth’s. We model the evolution of star-planet systems with host stars ranging from 1.0 to 3.5 MSun through-
out the post-main sequence, calculating stellar mass loss and its effects on planetary orbital evolution and atmospheric erosion. The maximum amount of time a rocky planet can spend continuously in the evolving post-MS habitable zone ranges between 56 and 257 Myr for our grid stars. Thus, during
the post-MS evolution of their host star, subsurface life on cold planets and moons could become re- motely detectable once the initially frozen surface melts. Frozen planets or moons, like Europa in our Solar System, experience a relatively stable environ- ment on the horizontal branch of their host stars’ evo- lution for millions of years.
331.02 — Exploring Giant Planets & Exomoons in the Habitable Zone.
Michelle Hill1; Stephen Kane1
1 Earth & Planetary Science, UC Riverside (West Hollywood, Cali- fornia, United States)
While the search for exoplanets has been focused pri- marily on trying to find Earth like planets, there have been discoveries of many different worlds that have caused us to revise our ideas as to what could be a potentially habitable planet. Interestingly a sig- nificant number of giant exoplanets (>3 earth radii) have been detected in the habitable zone of their star. These giant planets are likely gas giants and thus are not considered habitable on their own, but they each could potentially be host to large rocky exomoons which would also exist in the habitable zone. These moons, should they exist, will offer new ways to un- derstand the formation and evolution of planetary systems, and widen the search for signs of life out in the universe. The occurrence rates of these moons are related directly to the occurrence rates of giant planets in the habitable zone of their star, thus we estimated the frequency with which we expect giant planets to occur in the habitable zones. We then com- piled a proposed exoplanet target list to be used in the search for detectable exomoons and for perform- ing more detailed follow-up studies. We identified 121 giant planets whose orbits lie within either the optimistic habitable zone (OHZ) or the conservative habitable zone (CHZ). As well as the potential exis- tence of exomoons, these giant planets in the HZ of their star raise questions as to the formation and evo- lution of these systems. As giant planets are thought to form beyond the snow line these planets likely mi- grated inwards during their formation in order for them to reside in the HZ today. One possible ex- planation as to why these planets stopped migrating once they reached the HZ is that of orbital resonance with other planets. Thus we fit each of the 121 HZ gi- ant planets radial velocity (RV) data to confirm their orbital solution and look for linear trends to deter- mine if there were indications for additional plan- etary companions. Of the 121 giant planets tested, 51 showed indications of additional companions (> 3σ). Highlights of our calculations will be presented
along with up to date results from ongoing RV ob- servations of the most promising of these systems.
331.03 — Predicting the UV Emission of M dwarfs with Exoplanets from Ca II and H-α
Katherine Melbourne1; Allison Youngblood2; Aki
Roberge2; Sarbani Basu1; Kevin France3; Cynthia
Froning4; J. Sebastian Pineda3; Evgenya L. Shkolnik6;
Travis Barman5; R. O. Parke Loyd6; Elizabeth Newton7;
Isabella Pagano8; Sarah Peacock5; Joshua Schlieder2;
Adam Schneider6; David John Wilson4
1 Yale University (New Haven, Connecticut, United States) 2 NASA Goddard Space Flight Center (Greenbelt, Maryland, United States)
3 Astrophysical and Planetary Science, University of Colorado (Boulder, Colorado, United States)
4 University of Texas at Austin (Austin, Texas, United States) 5 University of Arizona (Tucson, Arizona, United States) 6 Arizona State University (Tempe, Arizona, United States) 7 Dartmouth College (Hanover, New Hampshire, United States) 8 National Institute of Astrophysics (Cantania, Italy)
Given the current capabilities of exoplanet detec- tion methods, M dwarf stars are excellent candi- dates around which to search for temperate, Earth- sized planets. The UV wavelength regime is impor- tant to evaluate the photochemistry of the planetary atmosphere because many molecules have highly wavelength dependent absorption cross sections that peak in the UV (900-3200 Å). M dwarfs are highly active stars with unique spectra that can drive the abiotic production of key planetary biosignatures. We seek to provide a broadly applicable method of estimating the UV emission of an M dwarf, with- out direct UV data, by identifying a relationship be- tween non-simultaneous optical and UV observa- tions. Our work uses the largest sample of low-mass star UV observations yet assembled, including data from the MUSCLES and Mega-MUSCLES Treasury Surveys (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems), the FUMES survey (Far Ultraviolet M-dwarf Evolu- tion Survey), and the HAZMAT survey (HAbitable Zones and M dwarf Activity across Time). We mea- sure Hα equivalent widths and the Mount Wilson CaII H&K S and R’HK indices using ground-based
optical spectra from the HARPS, UVES, and HIRES archives and new HIRES spectra. Archival and new Hubble Space Telescope COS and STIS spectra are used to measure line fluxes for the brightest chro- mospheric and transition region emission lines be- tween 1200-2800 Å. Our results show a correlation between UV line luminosity and CaII R’HKwith stan-
the best-fit lines. Correlations between UV luminos- ity and Hα or the S index are weak. The results pre- sented in this talk will be important for near-future allocations of competitive Hubble time as well as the post-Hubble era. We demonstrate that with a pre- cise R’HK measurement obtained from the ground
(e.g., 5-10% precision), the estimate of the intrinsic Lyα luminosity is∼12-20%, which is typically bet- ter than what can be achieved with direct, low-to- medium S/N Hubble spectra. After we gather more data this summer, we will also be able to detail de- pendencies on age and spectral type.
331.04 — 3-D Climate Models For Characterizing Habitable Terrestrial Extrasolar Planets
Ravikumar Kopparapu1; Anthony Del Genio2; Michael
Way2; Eric Wolf3; Thomas Fauchez1; Nancy Kiang2;
Linda Sohl2; Jacob Haqq-Misra4; Scott Guzewich1;
Stephen Kane5; John Armstrong6; Chester Harman2;
Kostas Tsigardis2; Daria Pidhorodetska1; Shawn
Domagal-Goldman1; Mark Marley7
1 NASA Goddard Space Flight Center (Greenbelt, Maryland, United States)
2 NASA GISS (New York, New York, United States)
3 University of Colorado-Boulder (Boulder, Colorado, United States) 4 Blue Marble Space Institute of Science (Seattle, Washington, United States)
5 U. California Riverside (Riverside, California, United States) 6 Weber State University (Ogden, Utah, United States) 7 NASA Ames (Moffet Field, California, United States)
While the recently discovered extrasolar planets have both challenged our imaginations and broad- ened our knowledge of planetary systems, per- haps the most compelling objective of exoplanet science is to detect and characterize habitable and possibly inhabited terrestrial worlds around other stars. In our quest to characterize habitable worlds, three-dimensional (3-D) general circulation models (GCMs) should be used to evaluate the potential climate states and their associated observable sig- nals. 3-D models allow for self-consistent and re- alistic simulations of the climates of terrestrial ex- trasolar planets around a variety of stellar spectral types. Future observatories have the capability to de- duce transmission, thermal emission, and reflectance spectra as a function of orbital phase. A complete un- derstanding of terrestrial exoplanetary atmospheres, gained through comprehensive 3-D modeling, is crit- ical for interpreting spectra of exoplanets. In this presentation, we will highlight the recent advances in 3-D climate model studies of habitable climates, and their impact on observables. We show that the current assumption of a (modern) Earth-analog as
a template for a habitable planet around other stel- lar spectral types is not a representative model for important features in the observed spectrum. Im- proving upon our models of habitability is particu- larly relevant for planets within the habitable zones of low-mass stars (late-K and all M-dwarfs), which might be amenable for characterization in the near future either with JWST or large ground-based tele- scopes or the mission study concept OST. Such im- provements will also be equally important for plan- ets around Sun-like stars due to different evolution- ary and planetary system history, which can be stud- ied by mission studies like LUVOIR and HabEX. The presentation will include potential synergies that can be fostered between theorists and observers, with a common goal of finding an inhabited exoplanet.
331.05 — Geochemistry of Carbon Cycles on Rocky Exoplanets
Kaustubh Hakim1; Pierre Auclair-Desrotour1; Russell
Deitrick1; Daniel Kitzmann1; Dan J. Bower1; Caroline Dorn2; Kevin Heng1
1 Center for Space and Habitability, University of Bern (Bern, Switzerland)
2 University of Zurich (Zürich, Switzerland)
The long-term carbon cycle (also known as the silicate-carbonate cycle) acting on a timescale of the order of hundreds of thousands of years provides the essential negative feedback to maintain temper- ate climates on Earth. With the discovery of almost a thousand rocky exoplanets and ongoing hunts for an Earth-twin, it is imperative to understand the work- ing of the carbon cycle on such planets. The aim is to investigate the factors of the Earth’s carbon cy- cle that are critical to stabilize and destabilize carbon cycles on rocky exoplanets. These factors could be dependent on the orbital, planetary and stellar pa- rameters as well as planet-specific properties such as rock composition, land and ocean fractions, among other factors. In this study, we focus on modeling the chemical kinetics of rock-water interaction for different rock types (depending on the planet’s sur- face composition), as well as pH. We incorporate a set of silicate weathering reactions leading to the for- mation of carbonates. In addition to continental sil- icate weathering, we explore the effects of seafloor weathering especially in the context of varying land- mass fractions, and shallow and deep ocean frac- tions. Other components of the carbon cycle such as subduction, ridge and arc volcanism are parameter- ized based on previous studies. The effects of planet size, oxidation states, and tidal locking are also in- vestigated.
331.06 — Stellar Flares and Habitable (?) M-dwarf Worlds: Exploring a New Sample with TESS
Maximilian N. Günther1
1 MIT (Cambridge, Massachusetts, United States)
Finding and characterizing small exoplanets tran- siting small stars naturally poses the question of their habitability. A major contributing factor to this might be stellar flares, originating from powerful magnetic reconnection events on the star. While too powerful flaring can erode or sterilize exoplanets’ at- mospheres and diminish their habitability, a mini- mum flare frequency and energy might be required for the genesis of life around M-dwarfs in first place. Here, I will highlight our study of stellar flares from the Transiting Exoplanet Survey Satellite (TESS). In the first year of TESS data, we already identified thousands of flaring M-dwarfs, most of which are rapidly rotating and of late spectral types. Our sam- ple includes superflares that showed over 30× bright- ness increase in white light. I will link our results to criteria for prebiotic chemistry, atmospheric loss through coronal mass ejections, and ozone steriliza- tion. Expanding this with upcoming TESS sectors, stellar flare studies will ultimately aid in defining cri- teria for exoplanet habitability.
331.07 — Abiotic Oxygen on Venus-Like Exoplan- ets Around M-Dwarfs
Michael L. Wong1,3; Victoria S. Meadows1,3; Peter Gao2;
Carver Bierson4; Xi Zhang4
1 Astronomy & Astrobiology, University of Washington (Seattle, Washington, United States)
2 University of California, Berkeley (Berkeley, California, United States)
3 Virtual Planetary Laboratory (Seattle, Washington, United States) 4 University of California, Santa Cruz (Santa Cruz, California, United States)
Terrestrial exoplanets in the habitable zones of nearby M dwarfs represent the first targets for the search for life outside of the Solar System. It has been long thought that one of the most obvious biosig- natures on alien worlds would be the spectroscopic detection of O2 and/or O3, created by a global bio-
sphere of photosynthetic life forms (Meadows et al., 2018). However, modeling has suggested that large amounts of O2can be created abiotically—especially on terrestrial planets around M dwarfs. In particu- lar, Gao et al. (2015) showed that desiccated worlds with CO2-rich atmospheres can build up ∼15% O2 via CO2photolysis. Venus, nonetheless, has little at-
mospheric O2, despite ongoing CO2photolysis. This
has been attributed to catalytic cycles involving ClOx
and SOxthat regenerate CO2from CO and O (Mills
et al., 2007; Yung & DeMore, 1999). We seek to ascer- tain how these cycles behave on Venus-like planets around different types of stars.
We have constructed a 1-D photochemical model based on Zhang et al. (2012) to study the atmospheric chemistry of Venus-like exoplanets. The model sim- ulates an atmosphere primarily composed of CO2
(∼90 bars) and N2 (∼3 bars) with trace amounts of H2O, SO2, HCl, and other constituents composed of H, C, O, N, S, and Cl, which contribute the HOx, ClOx, SOx, and NOx catalysts that can recombine photochemically generated CO and O into CO2. We compare the effect of G- and M-dwarf spectral en- ergy distributions on Venus-like worlds, placing the planets at orbital distances with the same total inci- dent flux as Venus.
We find that Venus-like worlds are rich in catalysts that can recombine CO and O into CO2. Around both
G and early M dwarfs, as the catalytic ClOxchem-
istry is sufficient recombine CO and O. We identify catalytic cycles involving Cl–S molecules that con- trol the buildup of large amounts of photochemi- cal O2 around late M dwarfs. Specifically, around TRAPPIST-1, low SO2mixing ratios significantly re- duces the action of Cl–S catalysts that scrub O2 and reconstitute CO2. This implies that Venus-like planets around late M dwarfs must maintain some amount of active SO2outgassing to be robust against
abiotic O2production.
331.08 — A laboratory-to-model approach to under- standing exoplanet biosignatures
Tiffany Kataria1; Scott Perl1; Pin Chen1; Laura M.
Barge1; Yuk L. Yung2
1 JPL/Caltech (Pasadena, California, United States)
2 California Institute of Technology (Pasadena, California, United States)
The assessment of exoplanet habitability is predom- inantly based on the measurement of biosignature gases, usually in the form of triplicate sets of CH4,
O2, CO2, and O3, among other molecules indicative
of life. Because exoplanets are distant, this is predi- cated on the ability to characterize atmospheres that would contain these gases at detectable limits for re- mote telescopes. However, this methodology often lacks a mechanism relating atmospheric detections to the potentially biogenic sources that emit these gases at the planetary surface. This can lead to mis- interpretations between abiotic signatures and truly biotic sources. Here we present a study to quantita- tively link surface processes and atmospheric chem-
istry for potentially habitable exoplanets using actual microbiological experiments. We will measure gas outputs from actual field samples of microbial com- munities that are from various ecosystems in which a multitude of major biogenic gases can be quantified. These measurements will serve as exoplanet surface inputs to the Atmsopheric-Rock-Ocean-Chemistry (AROC) model, which couples an aqueous geochem- istry code and KINETICS (a photochemistry code) to trace surface-to-atmosphere chemistry. In this way, we can to bridge the gap between exoplanet biosig- natures and the very biology and metabolisms found in nature. The results from this study can help guide the design of future ground- and space-based tele- scopes (e.g., JWST, ARIEL, ELTs, HabEx, LUVOIR, Origins) by identifying additional biosignatures that would help distinguish between atmospheric condi- tions that may or may not be conducive to life.
331.09 — Stellar Energetic Particle-induced radia- tion dose as a constraint on the habitability of ter- restrial exoplanets
Dimitra Atri1
1 New York University Abu Dhabi (Abu Dhabi, United Arab Emi- rates)
Space weather has a profound impact on plane- tary atmospheres and has the potential to disrupt hospitable environments on exoplanets. The ef- fect is more significant in case of close-in exoplan- ets around active stars. In addition to X-rays and EUV from stellar flares, energetic charged particles can ionize the atmosphere leading to photochemi- cal changes, result in atmospheric erosion and can enhance radiation dose on the planetary surface. Charged particles of GeV energies undergo hadronic interactions in the atmosphere producing secondary particles, a fraction of which traverse down to the surface with harmful biological effects. Using data from 70 major SPEs (Solar Particle Events) over the past century as a proxy, and using GEANT4 (CERN) Monte Carlo model, we simulate radiation dose in- duced by Stellar Energetic Particles on presently known habitable exoplanets for various atmospheric and magnetospheric conditions. This is the first com- prehensive study to quantify the effects of SEPs on exoplanets. We compare the results with experimen- tal radiobiology data and discuss its implications on constraining the habitability of terrestrial exoplanets.
331.10 — Transition from Eyeball to Snowball Driven by Sea-ice Drift on Tidally Locked Terres- trial Planets
Jun Yang1
1 Dept. of Atmospheric and Oceanic Sciences, Peking University (Beijing, Beijing, China)
Background: Among the ≈4000 confirmed exoplan- ets, most of them are orbiting around M dwarfs be- cause they are relatively easy to detect and M dwarfs are the most common type of star in the galaxy. About 15 exoplanets are most likely to have rocky compositions and meanwhile in the habitable zone within which the surface is temperate to maintain liquid water. These planets are the prime targets for future atmospheric characterizations of potentially habitable systems, especially the three nearby ones– Proxima b, TRAPPIST-1e, and LHS 1140b. Previ- ous studies suggest that if these planets have surface ocean they would be in an eyeball-like climate state: ice-free in the vicinity of the substellar point and ice- covered in the rest regions. However, an important component of the climate system–sea ice dynamics has not been well studied in their work.
Fundamental question: Would the open ocean of the eyeball-like climate be stable against a globally ice-covered snowball state? Or, could sea-ice drift