TY - JOUR
T1 - Characterizing Earth Analogs in Reflected Light
T2 - Atmospheric Retrieval Studies for Future Space Telescopes
AU - Feng, Y. Katherina
AU - Robinson, Tyler D.
AU - Fortney, Jonathan J.
AU - Lupu, Roxana E.
AU - Marley, Mark S.
AU - Lewis, Nikole K.
AU - MacIntosh, Bruce
AU - Line, Michael R.
N1 - Funding Information:
Y.K.F. is supported by the National Science Foundation Graduate Research Fellowship under grant DGE1339067. T.R. gratefully acknowledges support from NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. The authors thank the 2016 Kavli Summer Program in Astrophysics; its Scientific and Local Organizing Committees; the program founder, Pascale Garaud; and the Kavli Foundation for supporting the genesis of this work. This work was made possible by support from the UCSC Other Worlds Laboratory and the WFIRST Science Investigation Team program. The results reported herein benefited from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science (NExSS) research coordination network, sponsored by NASA's Science Mission Directorate. Certain essential tools used in this work were developed by the NASA Astrobiology Institute's Virtual Planetary Laboratory, supported by NASA under cooperative agreement No. NNA13AA93A. Computation for this research was performed by the UCSC Hyades supercomputer, which is supported by the National Science Foundation (award number AST-1229745) and UCSC.
Funding Information:
Y.K.F. is supported by the National Science Foundation Graduate Research Fellowship under grant DGE1339067. T.R. gratefully acknowledges support from NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. The authors thank the 2016 Kavli Summer Program in Astrophysics; its Scientific and Local Organizing Committees; the program founder, Pascale Garaud; and the Kavli Foundation for supporting the genesis of this work. This work was made possible by support from the UCSC Other Worlds Laboratory and the WFIRST Science Investigation Team program. The results reported herein benefited from collaborations and/or information exchange within NASA’s Nexus for Exoplanet System Science (NExSS) research coordination network, sponsored by NASA’s Science Mission Directorate. Certain essential tools used in this work were developed by the NASA Astrobiology Institute’s Virtual Planetary Laboratory, supported by NASA under cooperative agreement No. NNA13AA93A. Computation for this research was performed by the UCSC Hyades supercomputer, which is supported by the National Science Foundation (award number AST-1229745) and UCSC. We thank Cecilia Leung, Asher Wasserman, Daniel Thorngren, Eric Gentry, and Chris Stark for stimulating discussions and essential guidance. Finally, we thank the anonymous referee for greatly improving the quality of this manuscript.
Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/5
Y1 - 2018/5
N2 - Space-based high-contrast imaging mission concepts for studying rocky exoplanets in reflected light are currently under community study. We develop an inverse modeling framework to estimate the science return of such missions given different instrument design considerations. By combining an exoplanet albedo model, instrument noise model, and ensemble Markov chain Monte Carlo sampler, we explore retrievals of atmospheric and planetary properties for Earth twins as a function of signal-to-noise ratio (S/N) and resolution (R). Our forward model includes Rayleigh-scattering, single-layer water clouds with patchy coverage, and pressure-dependent absorption due to water vapor, oxygen, and ozone. We simulate data at R = 70 and 140 from 0.4 to 1.0 μm with S/N = 5, 10, 15, and 20 at 550 nm (i.e., for HabEx/LUVOIR-type instruments). At these same S/Ns, we simulate data for WFIRST paired with a starshade, which includes two photometric points between 0.48 and 0.6 μm and R = 50 spectroscopy from 0.6 to 0.97 μm. Given our noise model for WFIRST-type detectors, we find that weak detections of water vapor, ozone, and oxygen can be achieved with observations with at least R = 70/S/N = 15 or R = 140/S/N = 10 for improved detections. Meaningful constraints are only achieved with R = 140/S/N = 20 data. The WFIRST data offer limited diagnostic information, needing at least S/N = 20 to weakly detect gases. Most scenarios place limits on planetary radius but cannot constrain surface gravity and, thus, planetary mass.
AB - Space-based high-contrast imaging mission concepts for studying rocky exoplanets in reflected light are currently under community study. We develop an inverse modeling framework to estimate the science return of such missions given different instrument design considerations. By combining an exoplanet albedo model, instrument noise model, and ensemble Markov chain Monte Carlo sampler, we explore retrievals of atmospheric and planetary properties for Earth twins as a function of signal-to-noise ratio (S/N) and resolution (R). Our forward model includes Rayleigh-scattering, single-layer water clouds with patchy coverage, and pressure-dependent absorption due to water vapor, oxygen, and ozone. We simulate data at R = 70 and 140 from 0.4 to 1.0 μm with S/N = 5, 10, 15, and 20 at 550 nm (i.e., for HabEx/LUVOIR-type instruments). At these same S/Ns, we simulate data for WFIRST paired with a starshade, which includes two photometric points between 0.48 and 0.6 μm and R = 50 spectroscopy from 0.6 to 0.97 μm. Given our noise model for WFIRST-type detectors, we find that weak detections of water vapor, ozone, and oxygen can be achieved with observations with at least R = 70/S/N = 15 or R = 140/S/N = 10 for improved detections. Meaningful constraints are only achieved with R = 140/S/N = 20 data. The WFIRST data offer limited diagnostic information, needing at least S/N = 20 to weakly detect gases. Most scenarios place limits on planetary radius but cannot constrain surface gravity and, thus, planetary mass.
KW - methods: statistical
KW - planets and satellites: atmospheres
KW - planets and satellites: terrestrial planets
UR - http://www.scopus.com/inward/record.url?scp=85047335032&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85047335032&partnerID=8YFLogxK
U2 - 10.3847/1538-3881/aab95c
DO - 10.3847/1538-3881/aab95c
M3 - Article
AN - SCOPUS:85047335032
SN - 0004-6256
VL - 155
JO - Astronomical Journal
JF - Astronomical Journal
IS - 5
M1 - 200
ER -