THE K2-ESPRINT PROJECT I: DISCOVERY OF THE DISINTEGRATING R OCKY PLANET WITH A COMETARY HEAD AND TAIL EPIC 201637175B

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hours: EPIC 201637175b. The highly variable transit depths, ranging from ∼0% to 1.3%, are suggestive of a planet that is disintegrating via the emission of dusty efflu ents. We characterize the host star as an M-dwarf with Teff ≃ 3800. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and ( 4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. Th e latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better st atistical precision compared with the ground-based observations. We detect a significant “bump’ just after the t ransit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context o f a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet’s Hill spher e and effectively undergo ‘Roche lobe overflow’, even though the planet’s surface is likely underfilling its R oche lobe by a factor of 2. Subject headings:planetary systems—planets and satellites: detection, atmospheres