KOI-2700b - A Planet Candidate With Dusty Effluents on a 22-Hour Orbit

Kepler planet candidate KOI-2700b (KIC 8639908b) with an orbital period of 21.84 hours exhibits a distinctly asymmetric transit profile, likely indicative of the emission of dusty effluents, and reminiscent of KIC 1255b. The host star has $T_{\rm eff}$ = 4435 K, M = 0.63 $M_\odot$, and R = 0.57 $R_\odot$, comparable to the parameters ascribed to KIC 12557548. The transit egress can be followed for ~25% of the orbital period, and, if interpreted as extinction from a dusty comet-like tail, indicates a long lifetime for the dust grains of more than a day. We present a semi-physical model for the dust tail attenuation, and fit for the physical parameters contained in that expression. The transit is not sufficiently deep to allow for a study of the transit-to-transit variations, as is the case for KIC 1255b; however, it is clear that the transit depth is slowly monotonically decreasing by a factor of ~2 over the duration of the Kepler mission. The existence of a second star hosting a planet with a dusty comet-like tail would help to show that such objects may be more common and less exotic than originally thought. According to current models, only quite small planets with Mp < 0.03 $M_\oplus$ are likely to release a detectable quantity of dust. Thus, any "normal-looking" transit that is inferred to arise from a rocky planet of radius greater than ~1/2 $R_\oplus$ should not exhibit any hint of a dusty tail. Conversely, if one detects an asymmetric transit, due to a dusty tail, then it will be very difficult to detect the hard body of the planet within the transit because, by necessity, the planet must be quite small (i.e., < 0.3 $R_\oplus$).