Results from the NASA / NSF Extreme Precision Radial Velocity Working Group

Radial velocity measurements provide the minimum masses and orbits of exoplanets, and thus critical exoplanet demographics information. For planets with radial velocity observations that also transit or are directly imaged at multiple epochs, the true mass of the planet can be measured. The true mass of a planet is critical for correctly interpreting atmospheric spectra of both transiting and directly imaged planets. Following the recommendation of the U.S. National Academy of Sciences' Exoplanet Science Strategy Report, NASA and the NSF have formed a working group on Extreme Precision Radial Velocity (EPRV) measurements. This working group is focused on studying the next steps and investments necessary to measure the masses of Earth-mass planets in the habitable zones of Sun-like stars — planets that are expected to induce an RV semi-amplitude of only 9 cm/s on their host star. Reliable planet detections are currently limited to those with a RV semi-amplitude of roughly 1 m/s due to stellar activity, instrumental stability and calibration, and spectral contamination from telluric lines. Progress will require new instruments, substantial allocations of observing time, advanced statistical methods for data analysis informed by theoretical modeling, and collaboration between observers, instrument builders, stellar astrophysicists, heliophysicists, and statisticians. The working group has been tasked with recommending an EPRV investment strategy that would advance the state of the art to the point where masses and orbits can be measured for temperate, terrestrial planets around nearby Sun-like stars, preferably in time to influence the design and scheduling of a future direct imaging mission such as HabEx or LUVOIR. Upon receipt of the Working Group's report in spring 2020, NASA and NSF will consider if, when, and how to implement that strategy. I will present a summary of the Working Group's report to NASA and NSF, as well as updates on responses from the agencies.