Measuring masses of transiting Earth-like planets: first insights from the PLATO RV data challenge

The PLATO Stellar Variability Mitigation Working Group designed a radial velocity (RV) data challenge to assess the precision and accuracy achievable on RV semi-amplitudes in the context of the future PLATO follow-up. Using Sun-as-a-star observations obtained with HARPS-N, we generated three multiplanet systems with realistic sampling, an effective signal-to-noise ratio of (Formula presented), an exposure time of (Formula presented) min, and a total of (Formula presented) observations. The resulting data set is publicly available and can serve as a benchmark for the community to test and compare RV analysis methods. Eight independent teams participated in the challenge, aiming to recover the semi-amplitudes of both transiting and non-transiting planets. A meta-analysis of the submitted results shows that, with current data analysis methods, HARPS-N-like stability and the observing strategy studied in this paper, achieving a precision on semi-amplitudes better than 10 per cent for habitable-zone signals around a solar-type star is challenging, and is typically limited to planets with masses of (Formula presented) –10 (Formula presented). This performance is expected to improve for K dwarfs, where planets down to (Formula presented) –5  (Formula presented) may be characterized at a similar level of precision. Finally, based on the results of this challenge and the occurrence of false positives, we derive an empirical detection threshold for RV surveys, which can be used to distinguish robust planetary detections from candidates.