January 2020
Vol 6, Issue 3

About The Cover

Cover image expansion

ONLINE COVER A previous study of Proxima Centauri using the Atacama Large Millimeter/submillimeter Array (ALMA)—an astronomical observatory in northern Chile—reported an unknown source of light spectrum signals that could belong to a second planet or may simply have been the product of a neighboring galaxy or an unrelated phenomenon. To better understand if the signal originated from another planet orbiting the star, Damasso et al. analyzed a 17.5-year-long time series of high-precision radial velocities using an exoplanet detection method that tracks a star's light spectrum. They determined that the signal is likely unrelated to shifts in the star's magnetic field and may indicate the presence of a planet with a greater mass than Earth, although more evidence is needed to confirm its existence. If there is, in fact, a second planet orbiting Proxima Centauri, it could challenge models of how "super-Earths" are born—most are believed to form near the "snowline," the minimum distance from a star at which water can turn to solid ice, but the candidate planet's orbit lies far beyond this sweet spot. [CREDIT: LORENZO SANTINELLI]