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Debris Disks in Kepler Exoplanet Systems

The Kepler Mission recently identified 997 systems hosting candidate extrasolar planets, many of which are super-Earths. Realizing these planetary systems are candidates to host extrasolar asteroid belts, we use mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) to search for emission from dust in these systems. We find excesses around eight stars, indicating the presence of warm to hot dust (~100-500 K), corresponding to orbital distances of 0.1-10 AU for these solar-type stars. The strongest detection, KOI 1099, demands ~500 K dust interior to the orbit of its exoplanet candidate. One star, KOI 904, may host very hot dust (~1200 K, corresponding to 0.02 AU). Although the fraction of these exoplanet-bearing stars with detectable warm excesses (~3%) is similar to that found by Spitzer surveys of solar-type field stars, the excesses detectable in the WISE data have much higher fractional luminosities (Ldust/L*) than most known debris disks, implying that the fraction with debris disks of comparable luminosity may actually be significantly higher. It is difficult to explain the presence of dust so close to the host stars, generally corresponding to dust rings at radii <0.3 AU; both the collisional and Poynting-Robertson drag timescales to remove dust from the system are hundreds of years or less at these distances. Assuming a steady-state for these systems implies large mass consumption rates with these short removal timescales, meaning that the dust production mechanism in these systems must almost certainly be episodic in nature.