We report on the discovery of a transiting Earth-sized (0.95R⊕) planet around an M3.5 dwarf star at 57pc, K2-315b. The planet has a period of ∼3.14 days, i.e. ∼π, with an instellation of 7.45S⊕. The detection was made using publicly available data from K2's Campaign 15. We observed three additional transits with SPECULOOS Southern and Northern Observatories, and a stellar spectrum from Keck/HIRES, which allowed us to validate the planetary nature of the signal. The confirmed planet is well suited for comparative terrestrial exoplanetology. While exoplanets transiting ultracool dwarfs present the best opportunity for atmospheric studies of terrestrial exoplanets with the James Webb Space Telescope, those orbiting mid-M dwarfs within 100pc such as K2-315b will become increasingly accessible with the next generation of observatories.
@article{arxiv.2006.07308,
title = {$\pi$ Earth: a 3.14-day Earth-sized Planet from $\textit{K2}$'s Kitchen Served Warm by the SPECULOOS Team},
author = {Prajwal Niraula and Julien de Wit and Benjamin V. Rackham and Elsa Ducrot and Artem Burdanov and Ian J. M. Crossfield and Valerie Van Grootel and Catriona Murray and Lionel J. Garcia and Roi Alonso and Corey Beard and Yilen Gomez Maqueo Chew and Laetitia Delrez and Brice-Olivier Demory and Benjamin J. Fulton and Michael Gillon and Maximilian N. Gunther and Andrew W. Howard and Howard Issacson and Emmanuel Jehin and Peter P. Pedersen and Francisco J. Pozuelos and Didier Queloz and Rafael Rebolo-Lopez and Lalitha Sairam and Daniel Sebastian and Samantha Thompson and Amaury H. M. J. Triaud},
journal= {arXiv preprint arXiv:2006.07308},
year = {2020}
}