sign in sign up
<<
Home , Automated Planet Finder, Exoplanet, Jessie Christiansen, Small planet radius gap

ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 1 of 21

Approved by:

Dr. Gary Blackwood Date Program Manager, Exploration Program Office NASA/Jet Propulsion Laboratory

Dr. Douglas Hudgins Date Program Scientist Exoplanet Exploration Program Science Mission Directorate NASA Headquarters

EXOPLANET EXPLORATION PROGRAM Science Gap List 2020

Karl Stapelfeldt, Program Chief Scientist

Eric Mamajek, Deputy Program Chief Scientist Exoplanet Exploration Program JPL CL#20-1234 CL#20-1234 JPL Document No: 1717112 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 2 of 21

Cover Art Credit: NASA/JPL-Caltech. Artist conception of the K2-138 exoplanetary system, the first multi- system ever discovered by citizen scientists1. K2-138 is an orangish (K1) about 200 away, with five known all between the size of and orbiting in a very compact architecture. The planet’s orbits form an unbroken chain of 3:2 resonances, with orbital periods ranging from 2.3 and 12.8 days, orbiting the star between 0.03 and 0.10 AU. The limb of the hot sub-Neptunian world K2-138 f looms in the foreground at the bottom, with close neighbor K2-138 e visible (center) and the innermost planet K2-138 b transiting its star. The discovery study of the K2-138 system was led by and collaborators (2018, Astronomical Journal, Volume 155, article 57). This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This document has been cleared for public release (CL#19-0790).

© 2019 California Institute of Technology. Government sponsorship acknowledged.

1 https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA22088

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 3 of 21

Approved by:

Dr. Gary Blackwood Date Program Manager, Exoplanet Exploration Program Office NASA/Jet Propulsion Laboratory

Dr. Douglas Hudgins Date Program Scientist Exoplanet Exploration Program Science Mission Directorate NASA Headquarters

Created by:

Dr. Karl Stapelfeldt Date Chief Program Scientist Exoplanet Exploration Program Office NASA/Jet Propulsion Laboratory California Institute of Technology

Dr. Eric Mamajek Date Deputy Program Chief Scientist Exoplanet Exploration Program Office NASA/Jet Propulsion Laboratory California Institute of Technology

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 4 of 21

The 2020 Exoplanet Exploration Program (ExEP) Science Gap List

Compiled and maintained by: Dr. Karl Stapelfeldt, Program Chief Scientist Dr. Eric Mamajek, Deputy Program Chief Scientist NASA Exoplanet Exploration Program Jet Propulsion Laboratory, California Institute of Technology

The Exoplanet Exploration Program (ExEP) is chartered by the Division (APD) of NASA’s Science Mission Directorate (SMD) to carry out science, research, and technology tasks that advance NASA’s science goal to “Discover and study planets around other , and explore whether they could harbor .” ExEP’s three aims are:

 discovering planets around other stars,  characterizing their properties, and  identifying candidates that could harbor life

ExEP serves NASA and the community by acting as a point for exoplanet science and technology, managing research and technology initiatives, facilitating access to scientific data, and integrating the results of previous and current missions into a cohesive strategy to enable future discoveries. ExEP serves the critical function of developing the concepts and technologies for exoplanet missions, in addition to facilitating science investigations derived from those missions. ExEP manages development of mission concepts, including key technologies, as directed by NASA HQ, from their early conceptual phases into pre-Phase A.

The goal of the ExEP Science Plan2 is to show how the Agency can focus its science efforts on the work needed to realize the goal of finding and characterizing habitable , within the context of community priorities. The ExEP Science Plan consists of three documents, which will be updated periodically, which respond directly to the ExEP Program Plan [4]:

 ExEP Science Development Plan (SDP)  ExEP Science Gap List (SGL) (this document)  ExEP Science Plan Appendix (SPA)

The long-term online home of the science plan documents will be https://exoplanets.nasa.gov/exep/science-overview/.

2 Much of this preamble text is drawn from the longer introduction to the ExEP Science Plan Appendix (SPA), which provides further context for the ExEP Science Plan.

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 5 of 21

The ExEP Science Development Plan (SDP) reviews the program’s objectives, the role of scientific investigations in ExEP, important documentation, and the programmatic framework for ExEP science.

This document, the ExEP Science Gap List (SGL), tabulates program “science gaps”, which are defined as either:

 the difference between knowledge needed to define requirements for specified future NASA exoplanet missions and the current state of the art, or

 knowledge which is needed to enhance the science return of current and future NASA exoplanet missions.

Making the gap list public signals to the broader community where focused science investigations are needed over the next 3-5 years in support of ExEP goals. The ExEP Science Gap List represents activities and investigations that will advance the goals of NASA’s Exoplanet Exploration Program, and provides brief summaries in a convenient tabular format. All ExEP approaches, activities, and decisions are guided by science priorities, and those priorities are presented and summarized in the ExEP Science Gap List.

The Science Plan Appendix (SPA), lays out the scientific challenges that must be addressed to advance the goals of NASA’s Exoplanet Exploration Program. While the Program Science Development Plan is expected to remain stable over many years, the Science Gap List will be updated annually, and this Science Plan Appendix will be updated as needed approximately every two years. Entries in the Science Gap List will map to sections of the Science Plan Appendix.

The most recent community report relevant to the NASA ExEP is the National Academies’ Exoplanet Science Strategy (ESS) released in September 2018 [3]. The ESS report provides a broad-based community assessment of the state of the field of exoplanet science and recommendations for future investments. The National Academies also released the report An Strategy for the Search for Life in the in October 2018. NASA HQ is considering responses to the Exoplanet Science Strategy and Astrobiology Strategy reports. One response has been the chartering of the “Extreme Precision Working Group” (EPRV-WG), which will develop a blueprint for a strategic EPRV initiative to NASA and NSF in early 2020. The Astro2020 Decadal Survey is expected to strongly consider the recommendations of the ESS report, and their direction to NASA will guide priorities for the Astrophysics Division and Exoplanet Exploration Program.

The 2018 Exoplanet Science Strategy report provided “two overarching goals in exoplanet science”:

 to understand the formation and evolution of planetary systems as products of the process of , and characterize and explain the diversity of architectures, planetary compositions, and planetary environments produced by these processes, and

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 6 of 21

 to learn enough about the properties of exoplanets to identify potentially habitable environments and their frequency, and connect these environments to the planetary systems in which they reside. Furthermore, scientists need to distinguish between the signatures of life and those of nonbiological processes, and search for signatures of life on worlds orbiting other stars

The ESS also provided seven recommendations and thirty five findings. The ESS goals, recommendations, and findings are summarized in Appendix B of the ExEP Science Plan Appendix.

The ExEP science gaps do not appear in a particular order, and by being recognized on this list are deemed important. Currently the gap list is used as a measuring stick when evaluating possible new program activities: if a proposed activity could close a gap, it would be considered for greater priority for Program resources. The ExEP Science Gap List is not meant to provide strategic community guidance on par with a National Academies report (e.g. Decadal Survey, Exoplanet Science Strategy, etc.), but to provide program-level tactical guidance for program management within the evershifting landscape of NASA missions and mission studies. Funding sources outside NASA ExEP are free to make their own judgements as to whether or not to align the work they support with NASA’s Exoplanet Exploration goals. Science gaps directly related to specific missions in phase A-E are relegated to those missions and are not tracked in the ExEP SGL. However, science gaps that facilitate science investigations derived from those missions, or support pre-phase A studies, may appear in the SGL.

©2020 California Institute of Technology. Government sponsorship acknowledged.

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 7 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Spectral The study of planetary of small A handful of small Current and future JWST 01 characterization of atmospheres advances our exoplanets across a diverse exoplanets suitable for proposals to spectrally atmospheres of knowledge of planetary range of planet sizes and spectroscopy have been characterize small small exoplanets formation and evolution, compositions, stellar types, identified by RV and transiting planets. Small and can provide chemical and radiation surveys. HST transiting exoplanets evidence for biological environments e.g. transit transit spectra of these discovered with K2, See SPA section processes. There are few spectroscopy of small have marginal sensitivity TESS, and ground-based 6 (atmospheres & extant spectroscopic planets transiting cool and would only be able transit surveys, can be ) detections of atmospheres dwarf stars, high-contrast to detect -free H- observed with JWST. for exoplanets smaller than spectroscopy of small dominated atmospheres, WFIRST/CGI may be Neptune, even though they exoplanets orbiting solar- which are not expected able to spectrally dominate the exoplanet type (FGK-type) stars. for this class of objects. characterize atmospheres population. The first Temperate examples are of So far there are no of small planets orbiting constraints are being particular interest. Need imaging detections of the very nearest stars. obtained for the atmospheric targets that provide the small exoplanets. Mission concept studies composition of small most photons (orbiting for Astro2020 have temperate planets (i.e. sub- nearby, brightest stars for defined capabilities for ), but detection of their class). next generation of definitive spectral features observatories to study for temperate rocky planets Related gaps: limits to atmospheres of small is beyond the current precision on extracting exoplanets via transit capability. In order to spectra (gap SCI-03), need spectroscopy (e.g. remotely assess the for accurate ephemerides Origins, LUVOIR, frequency of habitable for scheduling HabEx) or direct imaging planets and life in the spectroscopic observations (e.g. LUVOIR, HabEx). galaxy, new observations (gap SCI-09), and facilities must be need for precursor surveys developed. to find direct imaging targets (gap SCI-10).

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 8 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Modeling exoplanet Spectral modeling is Ability to model the Modeling of Ongoing research by the 02 atmospheres essential for inferring the physical and chemical atmospheres accounting community. ExoPAG properties of exoplanet structure of exoplanet for varying formation SAG-10 (Cowan et al. atmospheres, identifying atmospheres and their mechanisms, 2015, PASP, 127, 311) See SPA section their most crucial emergent spectra, as a quantified the needs and 6 (atmospheres & diagnostics, and defining the function of the total chemistry, and expected results from biosignatures) design goals for future ; chemical migration. 3D transit spectroscopy. telescopes and instruments. composition; presence of circulation models of hot NASA ROSES programs condensates, & giant planets, modeling in the Planetary Sciences hazes; observer phase the impact of Division support angle; and the radiative nonuniform cloud cover, fundamental research on and energetic particle modeling atmospheric planetary atmospheres, fluxes incident from the chemistry and escape including their origin, host star. Understand how due to stellar XUV evolution, and the exchange of matter and emission and predicted characterization. NASA energy with exospheres, to spectral observations Astrobiology Program is lithospheres, hydrospheres, (e.g. HST, JWST, future now the Interdisciplinary and potentially biospheres missions, etc.). Series of Consortia for affect the observed papers on biosignatures Astrobiology Research properties of the papers in June 2018 (ICAR) including the atmosphere. Challenges issue of Astrobiology. NExSS research include determining Modeling of individual coordination network, composition and properties target systems (e.g. designed to foster of aerosols, understanding TRAPPIST-1 planets, interdisciplinary research chemistry (e.g. reaction Proxima Cen b). on aspects of exoplanet rates, photochemistry, atmospheres and climate mixing, etc.), radiative relevant to life and transfer modeling biosignatures. (including scattering prescriptions), 3D atmosphere dynamics (e.g. general circulation models). and high-fidelity simulations of

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 9 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress instrumental effects on the observed spectra. Laboratory measurements of key molecular and aerosol opacities in relevant physical conditions.

SCI- Spectral signature Systematic instrumental and Ability to reliably extract Community analyses of WFIRST SITs 03 retrieval stellar effects in timeseries physical parameters, such HST transit spectra and performing retrieval photometry and high as - of imaging spectra from experiments for CGI contrast images limit the temperature profile and e.g., GPI & SPHERE. imaging spectra and See SPA section ability to extract reliable abundances. Thorough Simple noise models community data 6 (atmospheres & spectra from residual stellar understanding of the limits predict JWST transit challenges. ExoPAG biosignatures) signals. Key physical of the data, including spectra and SAG 19 Exoplanet parameters such as spectral effects of correlated and coronagraphic Imaging Data Challenge slopes and molecular systematic noise spectra. Development of for ground-based abundances can be sources. Strategies for best practices over time coronagraphy. Data uncertain, and achieved data taking, calibration, to acquire exoplanet challenges planned by spectral sensitivity may be processing to mitigate spectra with HST and JWST ERS team for worse than the photon noise these issues for each JWST. Studies of transits. limit. Early spectral individual contamination by stellar detections have not instrument/observatory photospheric withstood reanalysis (e.g. and lessons learned for heterogeneities as Deming & Seager 2017, future work. limitation to extraction JGRP, 122, 53). of transiting exoplanet spectra (e.g. Rackham et al. 2018, ApJ, 122, 853), and stellar speckles as a limitation to extraction of direct imaging spectra of exoplanets (e.g. Rizzo et al. 2018, SPIE, 10698).

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 10 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Planetary system Measurements of Integrated exoplanet Ongoing microlensing, Ongoing community 04 architectures: distribution of planetary demographic results from RV, transit, and direct efforts for assessing occurrence rates for parameters (e.g. masses, transit, direct imaging, imaging projects occurrence rates for exoplanets of all radii, orbital elements) from RV, and microlensing continue to build close-in planets with sizes various techniques are surveys. Include effects of statistics. Examples: Kepler and K2 data, important both for Kepler DR25, the low Clanton & Gaudi (2016, reconciling results from constraining planet yield of direct imaging ApJ, 819, 125) for different discovery See SPA sections: formation and evolution detections of self-luminous demographics of methods (e.g. transit, 2 (exoplanet models, and for predicting planets, and microlensing exoplanets on wide radial velocity, popluations), yields of future missions. results from recent separation orbits (>2 microlensing, direct 3 (exoplanet The lack of integrated campaigns. Update AU) for M dwarfs. imaging), and factoring dynamics), exoplanet population studies periodically to include new Pascucci et al. (2018) in stellar data. 5 (properties of limits our understanding of surveys such as TESS, and study of distribution of Exoplanet Standard target stars) exoplanet demographics to correct the host star mass-ratios of planets Definitions and over a wide range of masses properties used in prior and their stars between Evaluation Team and radii. Extrapolations to surveys. The effect of microlensing and transit (ExSDET) investigating HZ demographics need to be measurement uncertain- methods. Meyer et al. reconciliation of Kepler on best basis (see SCI-05). ties on the results must be (2018, A&A, 612, L3) transit results (e.g. quantified. There is a need combined data from RV, ExoPAG13) with radial for planet formation microlensing, and velocity survey results. models which account for imaging surveys to There is a large the observed produce surface density community effort to demographics. distribution of gas giants validate TESS exoplanet in 1-10 MJ mass range candidates. ExoPAG SIG for M dwarfs over 0.07- 2 is synthesizing 400 au. Exoplanet available data on Population Observation exoplanet occurrence Simulator (EPOS) rates. WFIRST compares synthetic microlensing survey is planet population designed to measure models to observations occurrence rate of cold (e.g. Mulders et al. 2019, planet population. arXiv:1905.08804).

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 11 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Occurrence rates Subset of SCI-04 focusing Analysis of occurrence Published analyses by This is an active research 05 and uncertainties on occurrence rates for rates taking into account several authors, area. The community is for temperate Earth-sized planets in/near final Kepler data products including (e.g. Burke et working on planet rocky planets habitable zones, which (DR25), including effects al. 2015, ApJ, 809, 8; occurrence rate studies remains considerably of stellar multiplicity, and Traub 2016, that incorporate final (eta-Earth 휼 ) ⊕ uncertain. Critical to NASA improved stellar arXiv:1605.02255; Hsu Kepler DR25 data and for designing a large direct parameters - such that the et al. 2019, AJ, 158, 109; Gaia. imaging mission for remaining uncertainties are Pascucci et al. 2019, See SPA sections: detecting and characterizing dominated by intrinsic ApJ, 883, L15; Bryson Encourage observations 2 (exoplanet Earth analogs around nearby Kepler systematics. et al. 2019, : which can confirm popluations), stars. Reducing uncertainty 1906.03575). Gaia existence of candidate 5 (properties of in 휂 reduces uncertainty in Mission studies for results have improved temperate rocky planets target stars) ⊕ predicted yields for imaged Astro2020 adopted 휂⊕ = estimates of radii for all in Kepler data upon +0.46 and spectrally characterized 0.24 -0.16 for yield transiting planets (e.g. which 휂⊕ critically temperate rocky planets. calculations, informed by Fulton & Petigura 2018, relies. SAG 13 analysis (factor of AJ, 156, 264; Berger et 3× systematic al. 2018, ApJ, 866, 99). uncertainty). Analysis ExoPAG SAG 13 final work that reduces report helped inform mission concept studies. uncertainty in 휂⊕ would be beneficial to direct imaging mission concepts.

SCI- Yield estimation for Quantified, non-advocate Capability within NASA Stark et al. (2019, ExSDET completed its 06 exoplanet direct science yield comparisons Exoplanet Program to JATIS, 024009) show final report in fall 2019 imaging missions made on a common basis provide peer review of yield as function of using ExoSIMS package between various mission yield estimates made by aperture size and for exoplanet yield concepts, for both detections individual mission studies, astrophysical calculations, in See SPA section: and spectral using a transparent public assumptions, however a coordination with 2 (exoplanet characterizations. code implemented number of idealized members of concept popluations) Community agreement on independently, and assumptions were used. study teams, and key astrophysical input available for future proceeding with visibility assumptions. mission study trades. to stakeholders.

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 12 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Properties of known Improvement of Improved observational NExScI Exoplanet NExScI Exoplanet 07 exoplanet host stars measurement of exoplanet constraints on exoplanet Archive contains Archive is actively parameters needed for and host star properties are compilation of compiling data on See SPA section interpreting spectra rely needed to help inform the confirmed and candidate exoplanets and their host 5 (properties of directly on improvement of modeling of exoplanet exoplanets and their host stars. ExEP plans to post target stars) fidelity of stellar parameters atmospheres and stars, which can inform compiled target list based on photometry, interpretation of exoplanet mission concept studies informed by direct spectroscopy, , spectroscopy (SCI-02), focusing on studying imaging mission studies etc., and subsequent including: high energy transits or transit at NExScI in 2020. analysis. emission (e.g. UV, X-rays, spectroscopy/photometry flare properties), ages, of previously known Note: SCI-12 is for Improvement of knowledge precision stellar exoplanets, or direct improving knowledge of of stellar radii is outlined abundances for elements imaging of previously exoplanet radii separately in SCI-12. important to exoplanetary known exoplanets. Gaia (especially for structure/formation/ DR2 data on exoplanet deblending the evolution and biology. host star properties contributions from stellar Accurate elemental ingested into Archive. companions, both abundances and ages for physical and unphysical), M dwarf host stars are whereas SCI-07 focusses needed but have proved on improving knowledge challenging. Basic stellar of other stellar parameters (e.g. HRD parameters to help position, mass, , inform the interpretation etc.) are needed for non- and modeling of exoplanet hosts to enable exoplanet data (e.g. statistical studies. spectra). Improved knowledge of stellar, substellar, or planetary companions is helpful for interpretation of exoplanet properties and modeling (e.g. dynamics).

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 13 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Mitigating stellar Measurements of masses PRV: Earth orbiting at 1 PRV: Smallest claimed Major NASA investment 08 jitter as limitation and orbits are crucial for AU around a G2V star has RV amplitudes detected in PRV instrument to sensitivity of characterizing exoplanets, RV amplitude of ~9 cm/s, today are ~0.4 m/s for (NEID) for WIYN dynamical methods and for modeling their and Earth-mass planet in . Modern single (northern hemisphere 4- to detect exoplanets spectra and bulk corresponding HZ around measurement precision m class). NEID data for and measure their composition (see ESS report M2V star (~0.2 AU) has (SMP) among ongoing RV standard stars will be masses and orbits p. 4-30). PRV is currently RV amplitude of ~30 cm/s. RV surveys summarized made public the predominant means of RV jitter intrinsic to star is in Fischer et al. (2016, immediately. dynamically measuring at ~m/s level, and higher PASP, 128, 066001): Investigating options for See SPA sections: masses of exoplanets, and for active stars. Requires HARPS and HARPS-N archiving solar data with 3 (exoplanet stellar jitter dominates RV precision below 10 cm/s leading the way with 0.8 PRV spectrographs. dynamics), uncertainty budget. Stellar but accuracy at ~cm/s m/s. NEID in SAG-8 (Plavchan, 5 (properties of RV “jitter” in its various level so that systematic development (~0.3 m/s). Latham et al. 2015; target stars) forms (attenuation of errors do not dominate. Instrument systematics arXiv:1503.01770) convective blueshift by Major commitments of and stellar noise are not discussed effective use of stellar magnetic activity, observing time on well understood. SOA in the resources needed for granulation, non-radial telescopes with PRV PRV capabilities were confirming exoplanets. oscillations, etc.) is an ever- spectrographs needed. presented at EPRV4 Upon ESS present source of noise over Need new analysis workshop (March 2019). recommendation, NASA a variety of timescales for methods to correct for Astrometry: Studies on and NSF chartered both PRV and astrometric stellar RV jitter using high stellar astrometric jitter Extreme Precision Radial methods. While PRV is spectral resolution and of stars and the from Velocity Initiative capable of reaching Earth- broad spectral coverage. 2000s during Working Group in 2019 mass planets in HZs around PRV datasets for the Sun development phases for to provide community M dwarfs, it is not known enable testing and SIM and Gaia. Existing blueprint for agency whether current limits to improvement of mitigation ground-based astrometry support of EPRV PRV can be overcome to strategies. Reaching (CHARA, NPOI, VLTI) progress through 2020s detect Earth-like planets requisite velocities for cannot reach accuracy (report to be delivered orbiting solar-type (FGK) characterizing temperate required. Gaia is early 2020). stars. If technological gap of rocky planets for stars collecting data that achieving sub-휇as-level hotter than ~F7, and/or should lead to astrometry is achievable, with high vsini, astrometric detections of and astrometric jitter could representing tens of % of giant exoplanets. be understood/modeled at nearby direct imaging

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 14 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- sub-휇as-level, then targets, is even more 08 astrometry could provide an challenging. (cont.) alternative method which Astrometry: Exo-Earth could yield orbits and orbiting 1 MSun star at 10 masses for rocky planets pc induces amplitude of around nearby stars. Note: ~0.3 휇as. Predicted technology needs for EPRV astrometric amplitudes for and astrometry are tracked 1 MEarth planets at EEID separately in ExEP for large direct imaging Technology Gap List. mission targets within 30 pc range are predominantly between 0.1-1 휇as. For Sun-like activity levels, astrometric jitter would be ~0.05 휇as – small, but not negligible (but higher for more active stars). Develop capability to perform precision astrometry on nearby bright stars as precursor or followup for large direct imaging mission, as backup to PRV for detecting temperate rocky planets and measuring their masses and orbits.

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 15 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Dynamical Exoplanet candidates There are insufficient Keck HIRES limitation The NEID instrument 09 confirmation of detected via various precision RV resources for Kepler/K2 exoplanet has been delivered to exoplanet methods require available to the community confirmation is available WIYN and is being candidates and confirmation and to follow up all K2 and time, not instrument commissioned at time of determination of measurement of masses (the TESS candidates that may precision. At 200 new writing. Community their masses and majority discovered be relevant to JWST Kepler/K2 validations access is expected to start orbits presently and in near future spectroscopic study. per year, would need 4 in 2020A. NASA will be via transit method, Follow up K2 and TESS years to achieve 50%. community access to e.g. K2, TESS). Mass candidates with quick look For TESS, initial Keck HIRES and See SPA sections: constraints are crucial for low-precision RV screening of science eventually the new Keck 2 (exoplanet understanding atmospheric screening for false team targets is ongoing KPF instrument. populations), spectra and planetary bulk positives (e.g. eclipsing with LCOGT, Euler, Options for additional 3 (exoplanet density / composition. binaries), then high OHP, Magellan/PFS, southern hemisphere dynamics), Ephemerides need to be precision (~1-5 m/s) to HARPS and HARPS-N community PRV access 5 (properties of known precise enough to determined masses of the for precise follow-up at are being explored. US target stars), support scheduling of transit best candidates. TESS ~1 m/s on the best ~100 community is adding 6 (atmospheres & spectroscopy. follow-up requires PRV candidates (expect new spectrograph biosignatures) observing time in N and S measured masses for capabilities (e.g. hemispheres. Overall, only 50). TTV: e.g. MAROON-X on TESS will generate ~15k analysis of Kepler multi- -N, etc.). candidates of which planet systems; Spitzer ~1,250 should be detected Space Telescope in the 2-min cadence data, campaign observing with ~250 smaller than 2 transits in 7-planet REarth (Barclay et al. 2018, TRAPPIST-1 system. Ap.J.S. 239 2). Modeling of transit timing variations (TTVs) can be used for transiting multi-planet systems; further observations can improve orbits and masses. Transit epochs need to be known to within a few hours.

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 16 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Precursor Advance screening of For the most likely targets Howard & Fulton (2016, EPRV Working Group 10 observations of targets can determine which of future direct imaging PASP, 128, 4401) will recommend direct imaging stars to prioritize for future missions, assess the completed analysis for precursor observations targets exoplanet spectral detection limits provided 2014 versions of and datasets which may characterizations. Refine by existing PRV WFIRST, Exo-S, and be added to NExScI target lists (originally data. Improve these limits Exo-C target lists using Exoplanet Archive. See SPA sections: created during concept through a precision RV data from California ExEP chief scientists will 3 (exoplanet studies) and improve basic observing program in both planet search. Southern post new catalog of dynamics), stellar parameters for targets N and S hemispheres, target stars are lacking. NASA mission targets 5 (properties of for direct imaging missions executed consistently over There are published (and (targets identified in target stars), taking into account new > 5 years. ESA Gaia unpublished) RV data studies for direct imaging 6 (atmospheres & observations. PRV and/or mission astrometry (final for many potential large and probe mission biosignatures) astrometric observations are data release in early WFIRST targets. Butler concepts) to motivate desired in order to (1) detect 2020s) may reveal et al. (2017, AJ, 153, community observations (or constrain presence of) evidence of astrometric 208) published 61k RVs and analysis of these planets for potential spectral perturbations by measured over 20 years systems. NEID GTO characterization, and (2) exoplanets which could be for stars in Lick- program on WIYN is detect stellar companions targets for direct imaging. Carnegie Exoplanet surveying ~20% of which may limit efforts to Constraints on stellar Survey, including many NASA Mission Targets. detect small planets using multiplicity from high mission targets. EXPRES GTO program high contrast imaging. resolution imaging needed Facilities: Keck HIRES, on DCT is surveying Increasing levels of stellar for assessing whether Lick APF, EXPRES, ~10-15% of NASA characterization are needed given star is an adequate HARPS-N, HARPS, Mission Targets. Priority going from input target star target for direct imaging NEID coming online of precursor work on to known exoplanet host star (starlight suppression soon. Precursor WFIRST CGI targets is (see SCI-07), in order to performance is affected by catalogs: ExoCat-1 unclear due to the prepare for analysis and neighboring stars). represents the most instrument’s current tech interpretation of exoplanet complete publicly demo status. spectra. available catalog, but is incomplete and becoming out of date. TESS mission has TESS Input Catalog (version 8 is most recent).

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 17 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress SCI- Understanding the is a noise Statistical knowledge of Images are available The LBTI team is 11 abundance and source that compromises the level of exozodiacal showing the substructure assessing the cost and distribution of imaging and spectroscopy of dust relative to the level in of cold () science value of several exozodiacal dust small planets in and around our is needed debris disks as seen by upgrades that would the habitable zones of for nearby FGK stars that HST, ground adaptive increase the sensitivity of nearby stars. Substructure will be the targets of future optics, Herschel, and their instrument. See SPA section in the exozodi distribution exoplanet direct imaging ALMA. There is a rich WFIRST CGI scientists 11 (exozodiacal dust) may mimic the presence missions. Mission yield literature of theoretical are working to quantify of an exoplanet and thus simulations of how the models of what sensitivity their confuse searches made with current best estimates of structure treating such instrument might be able smaller telescope exozodi dust levels affect effects as dust radial to achieve to exozodiacal apertures. To date, the integration times and transport and planetary dust in a survey of substructure in the achievable signal-to-noise perturbations on debris nearby stars, should distribution of habitable ratios for detection and disk structure. The NASA decide to re- zone dust has been mapped characterization, as a LBTI HOSTS survey instate a science program only for the case of our own function of mission has measured the mid-IR for that instrument. The solar system. architecture. Simulations excess emission due to capabilities of current of scenes as viewed by warm exozodiacal dust near-IR interferometers future imaging missions, in the habitable zones of and upcoming ELTs to quantifying the 38 stars (Ertel et al. constrain warm exozodi effectiveness of multi- subm.), finding a median levels need to be epoch observations to exozodi level 4× that of assessed. discriminate exozodi the solar system but with clumps from planets. a large 1휎 uncertainty of Directly observed images 7 zodis. While the of exozodi disks in the yields of exoplanet habitable zone would be direct imaging missions very valuable, if they were are a weak function of sensitive down to the ~5 the exozodi level (Stark zodi level and had the et al 2015, ApJ, 808 resolution to show 139), the quality of substructures and validate spectra of Earth analogs theoretical simulations. becomes problematic for telescope apertures < 4

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 18 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress m if the exozodi level is > +1 휎 from the LBTI median result. Further observational work that reduced the uncertainty in the median exozodi level would reduce the risk of marginal spectroscopic science return by future direct imaging missions.

SCI- Measurements of Measurements of accurate High resolution imaging in NESSI speckle camera Continued NASA 12 accurate transiting exoplanet radii are bulk to validate K2 and at WIYN offers ability to support for community planet radii important for: classification TESS candidates. Access screen a subset of targets access to speckle of planets, estimating their to observatories equipped to very small cameras on WIYN, densities, modeling with AO or speckle separations. SOAR Gemini-N and Gemini-S. See SPA sections: compositions, atmospheres, imaging cameras and HRCam (speckle), and 2 (exoplanet and spectra, and discovering turnkey pipelines, is ground-based AO Note: SCI-12 is for populations), trends important to needed in both N and S observations with e.g., improving knowledge of 5 (properties of understanding planet hemispheres. TESS will Robo-AO, Keck/NIRC2, exoplanet radii target stars) formation and evolution. discover >15k exoplanet VLT/NACO, etc. have (especially for The accuracy of measured candidates and would need helped validate KOIs. deblending the exoplanet radii is limited by to measure >1k stars/yr to Gaia DR2 photometry & contributions from stellar the accuracy of measured complete the work within astrometry resolves companions, both stellar radii, which can be a decade. Support work bright multiples, and physical and unphysical), dominated by the effects of that improves estimation provides parallaxes for whereas SCI-07 focusses blending of light by of stellar and exoplanet improving radii on improving knowledge companion stars (some of parameters for discovered estimates. High of other stellar which may be bound exoplanet systems. resolution spectroscopy parameters to help companions). Detailed Supporting photometric can reveal spectroscopic inform the interpretation observations are needed to and spectroscopic stellar binaries, and injection and modeling of derive accurate stellar radii. data, along with and recovery tests can exoplanet data (e.g. The large number of TESS astrometric, photometric, place further quantitative spectra).

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 19 of 21

ID Title Summary Capability Needed Capability Today Mitigation in Progress exoplanet candidates and and spectroscopic data constraints on high expected contamination from latest Gaia data companions. For rates (20˝ pixels) drives releases, are critical for improving knowledge of requirement for large accurately assessing stellar host star Teff, metallicity, community effort to parameters – and : high-res. measure accurate stellar and exoplanet radii. For spectroscopy surveys exoplanet radii and assess occurrence rate studies, (e.g. California-Kepler multiplicity. Not accounting accurate limiting radii for survey), lower res. for light contamination by planet detection for transit Spectroscopy surveys neighboring stars, or poor survey stars for which (e.g., APOGEE & stellar characterization, can transiting planets were not LAMOST), and lead to exoplanet radii detected is also important. community access to systematically miscalculated spectrographs for at the tens % level. extracting stellar spectra Complete vetting of TESS (e.g. Keck HIRES, targets with Kepler NEID, CHIRON, etc.). approach could take SOA reviewed at “Know decades. TESS (including Thy Star – Know Thy FFIs) will generate 10× Planet” Conference in more candidates than 2017. Kepler, and AO and speckle imaging validation of Kepler prime mission candidates took ~3 years.

Improvement in knowledge of other stellar parameters relevant to interpreting exoplanet data is outlined separately in SCI-07.

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 20 of 21

APPENDIX A: ACRONYM LIST

ALMA Atacama Large Millimeter Array APF (robotic 2.4-m optical telescope at ) CGI Instrument (on WFIRST) CHARA Center for High Angular Resolution DR Data Release EC Executive Committee EEID Earth Equivalent Insolation Distance (EEID; aEEID = √퐿 au where L is stellar luminosity in solar units) EPRV Extreme Precision Radial Velocity ERS Early Release Science (JWST program) ESS Exoplanet Science Strategy (2018) National Academies Report ExEP Exoplanet Exploration Program Exo-C Exo-Coronagraph (Probe Study) Exo-S Exo-Starshade (Probe Study) ExoPAG Exoplanet Program Analysis Group ExoSIMS Exoplanet Open-Source Imaging Mission Simulator ExSDET Exoplanet Standard Definitions and Evaluation Team FFI Full Frame Images GCM General Circulation Model GI Guest Investigator GPI GTO Guaranteed Time Observations HabEx Habitable Exoplanet Imaging Mission HARPS High Accuracy Radial velocity Planet Searcher HARPS-N High Accuracy Radial velocity Planet Searcher-North HATNet Hungarian-made Automated Telescope Network HIRES High Resolution Echelle Spectrometer HOSTS Hunt for Observable Signatures of Terrestrial Planetary Systems HST HZ Habitable Zone IRTF NASA Infrared Telescope Facility JWST James Webb Space Telescope KELT Kilodegree Extremely Little Telescope KPF Keck Planet Finder JPL Jet Propulsion Laboratory JWST James Webb Space Telescope KOI Kepler Object of Interest LBT Large Binocular Telescope LBTI Large Binocular Telescope Interferometer LCOGT Las Cumbres Observatory Global Telescope Network LUVOIR Large UV/Optical/IR Surveyor

Exoplanet Exploration Program JPL CL#20-1234 ExEP Science Gap List, Rev C JPL D: 1717112 Release Date: January 1, 2020 Page 21 of 21

NASA National Aeronautics and Space Administration NEID NN-explore Exoplanet Investigations with NESSI NASA Exoplanet Star (and) Speckle Imager NExScI NASA Exoplanet Science Institute NPOI Navy Precision Optical Interferometer PRV Precision Radial Velocity PTF Palomar Transient Factory RV Radial Velocity SAG Science Analysis Group SGL Science Gap List SMD Science Mission Directorate SMP Single Measurement Precision SIG Science Interest Group SIT Science Investigation Team STDT Science and Technology Definition Team TBD To Be Determined TESS Transiting Exoplanet Survey Satellite TPF Finder VLTI Interferometer WASP Wide Angle Search for Planets WIYN Wisconsin, Indiana, Yale, NOAO Observatory WFIRST Wide-Field Infrared Survey Telescope

Exoplanet Exploration Program JPL CL#20-1234