Pathways to Discovery in Astronomy and Astrophysics for the 2020s (2023) / Chapter Skim
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Appendix E: Report of the Panel on Exoplanets, Astrobiology, and the Solar System
Appendix E: Report of the Panel on Exoplanets, Astrobiology, and the Solar System
Pages 291-310
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From page 291... ...
Complementing our studies of individual worlds, multiple techniques have pieced together a broad understanding of exoplanet classes, enabling a new era of comparative planetary system science as we work toward a more complete census. Even though exciting progress has been made, significant key advances are still needed to place the solar system and our inhabited Earth in its cosmic context.
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From page 292... ...
This search is now within our scientific and technological reach, and can be informed by studies of larger exoplanets and solar system analogs, as well as interdisciplinary efforts that incorporate theory and laboratory investigations. The next section outlines key discoveries in the past decade that set the stage for exciting future advances.
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From page 293... ...
A more complete census would be needed to determine if our solar system is unusual in having a Jupiter, which has large implications for planetary evolution and the delivery of "volatiles" -- water and key compounds involving C, H, N, and O that condense at lower temperatures -- which can be delivered to drier inner planets by more bodies that form farther out. The Distribution and Nature of Sub-Neptune Planets Three of Kepler's key discoveries were that sub-Neptunes (1–4 Earth radii)
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From page 294... ...
Exoplanet Characterization and Solar System Synergy Efforts to characterize and model exoplanet atmospheres have focused largely on giant and Neptunesize planets; atmospheric characterization of smaller planets has just begun. Comprehensive surveys of transiting planets across a range of mass, radius, orbits, and/or insolation levels have provided key insights into interior and atmospheric composition, as well as the atmospheric circulation, chemical, and radiative properties that regulate planetary atmospheres.
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From page 295... ...
Astrophysics Assets and Solar System Science The planetary science community has made valuable use of astrophysics assets such as HST, Spitzer, and Kepler to explore solar system targets, which in return advance exoplanet science and astrobiology. Planetary scientists have measured the composition and orbital dynamics of small bodies to better understand solar system formation; observed diverse planetary atmospheres to assess how planetary processes are affected by composition and incident solar radiation; probed the interiors of volatile-rich bodies and identified new potentially habitable environments through the study of plumes on Europa and Enceladus; and observed the effects of extreme tidal heating on Io's interior composition and volcanic activity.
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From page 296... ...
Observations and missions to small bodies in the solar system illuminated processes of volatile evolution and delivery to forming planets, while exoplanet science revealed planetary system architecture influences on small body inventories and organic delivery in debris and protoplanetary disks. Venus provided context for loss of habitability, with relevance for Venus-analog extrasolar planets, and studies of stellar wind/planetary atmosphere interactions at Mars discovered and informed planetary atmospheric loss processes.
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From page 297... ...
The Nancy Grace Roman Space Telescope microlensing survey is poised to greatly expand our knowledge to longer orbital periods and lower planet masses across a wide range of stellar spectral types, filling key gaps in the census and providing a statistical anchor for planet formation and evolution models. Much like the Kepler data set revealed a gap in planet radii indicative of atmospheric evaporation, these extended demographics should give insight into physical processes governing planetary systems -- for example, by detecting an enhanced density of planets near the snowlines of systems.
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From page 298... ...
With more debris disks resolved at mm wavelengths, via improved sensitivity to fainter disks, samples of known planet host stars and disk host stars will begin to overlap, enabling studies of dynamical interactions between exoplanets and disks (compare the Discovery Area section in Appendix F)
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From page 299... ...
atmospheres for some of these transiting worlds, but further characterization via transit or high-contrast reflected-light spectroscopy should be feasible with facilities like JWST and the ELTs. In the near term, transit photometry and RV surveys will find many more of these M dwarf systems, although some may be too distant for atmospheric characterization.
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From page 300... ...
These data will be complemented by transmission and emission spectra of transiting planets spanning nearly the entire range of exoplanet masses, sizes, and temperatures, especially with the expanded spectral range and enhanced sensitivity of JWST. More precise high-frequency radio observations can be used to increase the sample of planets known to have magnetic fields, and lower-frequency observations can detect the weaker magnetic fields that are more likely to be present in ice giant and smaller gas giants.
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From page 301... ...
E-Q2d. How Does a Planet's Interaction with Its Host Star and Planetary System Influence Its Atmospheric Properties over All Time Scales?
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From page 302... ...
To identify habitable environments and connect them to the planetary systems in which they reside, foundational research on exoplanet properties and processes through observations of planets, disks, and planetary systems and theoretical models, laboratory studies, and comparisons with solar system analogs is needed.
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From page 303... ...
Exoplanet surveys have shown that terrestrial planets can exist around a range of stellar types, but observations have yet to confirm if habitable environments can exist around all types of stars. Although M dwarf planets will be the first accessible to near-term observation, they are far more likely than Sun-like stars (FGK dwarfs)
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From page 304... ...
HOW CAN SIGNS OF LIFE BE IDENTIFIED AND INTERPRETED IN THE CONTEXT OF THEIR PLANETARY ENVIRONMENTS? Over the next 10 years, JWST and upcoming ground-based telescopes will have the opportunity to conduct the first searches for signs of life on terrestrial planets orbiting a handful of nearby M dwarf stars.
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From page 305... ...
The next decade will present several opportunities to characterize terrestrial exoplanets and undertake the very first search for biosignatures on a handful of planets orbiting nearby M dwarfs. Owing to their host stars' super-luminous pre-main sequence phase, activity, and the proximity of the HZ to the star, M dwarf planets likely undergo a very different evolutionary history -- which may include atmosphere and ocean loss -- than planets orbiting more Sun-like stars and may allow us to expand our understanding of biospheres for different stellar hosts.
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From page 306... ...
By using a larger sample size that includes a range of FGKM stars, we improve our chances of finding inhabited planets, and understanding how the stellar environment impacts them. Direct Imaging While transmission observations will likely work well for M dwarf planets, direct imaging is needed to study the atmospheres of planets orbiting Sun-like FGK stars.
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From page 307... ...
E-Q2d: How does a planet's interaction with its host star and planetary system influence its atmospheric properties over all time scales? E-Q2e: How do giant planets fit within a continuum of our understanding of all substellar objects?
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From page 308... ...
to search for biosignatures ~1e-10, IWA <~60 mas, OWA ~500 mas, E-Q3d, ~100s of stars, R ~150 spectroscopy for E-Q4c, potentially dozens of Earth analogs) E-DA Astrometry E-Q1, Gaia, Roman WFI supplement: population studies Near-IR astrometry to measure substellar E-Q2a, overlapping with Kepler, cold gas giants in TESS object masses/orbits; masses and orbits of E-Q2b, and nearby systems temperate planets orbiting FGKM stars E-Q2c, E-Q2e, E-Q3d, E-DA Polarization E-Q1d, Roman: polarization of disks Direct imaging to probe polarized ocean E-Q1e, Ground-based instruments, including on ELTs: glint on terrestrial planets E-Q2c, polarization signatures of disks and giant planets E-Q2e, E-Q3c, E-Q3d, E-Q4, E-DA Microlensing E-Q1a Roman population studies Transit observations E-Q1b, TESS: discover and measure radii of inner planets, Large collecting area: detection of extremely E-Q1c, evaporated cores, and migrated planets orbiting small (terrestrial, <1.6 Earth radius)
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From page 309... ...
Radio observations >10 GHz and high resolution Lyman alpha (>~30,000) for photoevaporation and inferring stellar mass loss rates UV observations of E-Q2a, HST limited UV transit capability UV space telescope: R >1,000 spectroscopy; planets and host stars E-Q2c, monitor atmospheric escape; high-contrast E-Q2d, imaging of planets to detect UV absorbers; E-Q3c time-resolved UV stellar flux High-resolution O/IR E-Q2a, R >~1e5 O/IR spectroscopy (8–10 m telescopes)
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From page 310... ...
Marley et al., 2016, "The Need for Laboratory Work to Aid in the Understanding of Exoplanetary Atmospheres," arXiv preprint arXiv:1602.06305. NOTE: IWA/OWA: inner and outer working angles for optimum starlight suppression in direct imaging systems; R: spectral resolution; P: planetary orbital period; CGI: coronagraphic instrument; E/PRV: extreme/precision radial velocity; NEID: NN-EXPLORE exoplanet investigations with Doppler spectroscopy; GPI: giant planet imager; SPHERE: Spectro-Polarimetric High-Contrast Exoplanet Research; Roman WFI: Roman Wide-Field Imager; CME: coronal mass ejection.
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