KIC 8462852: Transit of a Large Comet Family

Abstract

We investigate the plausibility of a cometary source of the unusual transits observed in the KIC 8462852 light curve. A single comet of similar size to those in our solar system produces a transit depth of the order of $10^{-3}$ lasting less than a day which is much smaller and shorter than the largest dip observed ($\sim20\%$ for $\sim3$ days), but a large, closely traveling cluster of comets can fit the observed depths and durations. We find that a series of large comet swarms, with all but one on the same orbit, provides a good fit for the KIC 8462852 data during Quarters 16 and 17, but does not explain the large dip observed during Quarter 8. However, the transit dips only loosely constrain the orbits and can be fit by swarms with periastrons differing by a factor of 10. To reach a transit depth of $\sim0.2$, the comets need to be in a close group of $\sim30$, if they are $\sim100$ km in radius or in a group of $\sim300$ if they are $\sim10$ km in radius. The total number of comets required to fit all of the dips is $\sim70$ $\sim$100 km or $\sim700$ $\sim10$ km comets. A single comet family from a tidally disrupted Ceres-sized progenitor or the start of a Late Heavy Bombardment period explains the last $\sim60$ days of the unusual KIC 8462852 light curve.