Low-Mass M Dwarfs Lack Jupiter Analogs

Fully convective M dwarfs comprise over half of stars in the solar neighborhood. These tiny stars are ideal for exoplanet characterization, representing the only hosts amenable to transmission spectroscopy of terrestrial planet atmospheres with JWST and the ELTs. Understanding how planet formation and evolution differ around these tiny stars is essential if we hope to extrapolate studies of their terrestrial worlds to the currently unknowable population of Earth-like exoplanets around solar analogs. Arguably the most important feature is the presence or absence of Jovian worlds. For the terrestrial planets of our own solar system, Jupiter was an important influence: it sculpted the dynamical environment in which these worlds formed, affecting the delivery of volatiles, the terrestrial refractory budget, and, potentially, Earth's overall habitability. In our work, we investigated the occurrence rate of cold Jovian planets around inactive, low-mass (0.1-0.3M⊙) M dwarfs by monitoring a volume-complete sample of the 200 such stars within 15pc, collecting four high-resolution spectra of each M dwarf over a span of six years. We did not detect any Jupiter-mass planets at Jupiter-like instellations, allowing us to place a 95%-confidence upper limit of 1.7% on the occurrence rate of Jupiter analogs. In contrast, surveys of Sun-like stars have found that their giant planets are most common just beyond the snow line, at these Jupiter-like instellations. Our results indicate that architectures analogous to our solar system are rare around low-mass M dwarfs, in agreement with predictions of giant planet formation by core accretion. Moreover, these findings have significant ramifications for the evolution and habitability of the abundant terrestrial worlds that orbit these tiny stars.