KOI-2700b—A PLANET CANDIDATE WITH DUSTY EFFLUENTS ON A 22 hr ORBIT

Abstract

Kepler planet candidate KOI-2700b (KIC 8639908b), with an orbital period of 21.84 hr, exhibits a distinctly asymmetric transit profile, likely indicative of the emission of dusty effluents, and reminiscent of KIC 1255b. The host star has T [subscript eff] = 4435 K, M [~ over _] 0.63 M [subscript ☉], and R [~ over _] 0.57 R [subscript ☉], 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 semiphysical 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. We infer a mass-loss rate in dust from the planet of ~2 lunar masses per Gyr. 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 M[subscript p] [< over ~] 0.03 M [subscript ⊕] 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 [subscript ⊕] 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., [< over ~] 0.3 R [subscript ⊕]).