Possible Disintegrating Short-Period Super-Mercury Orbiting Kic 12557548

Abstract

We report here on the discovery of stellar occultations, observed with Kepler, that recur periodically at 15.685 hour intervals, but which vary in depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a V = 16 magnitude K dwarf with T eff,s 4400 K. The out-of-occultation behavior shows no evidence for ellipsoidal light variations, indicating that the mass of the orbiting object is less than ∼3 M J (for an orbital period of 15.7 hr). Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. This scenario seems ruled out by the dynamical instability that would result from such a configuration. We also briefly consider an eclipsing binary, possibly containing an accretion disk, that either orbits KIC 12557548 in a hierarchical triple configuration or is nearby on the sky, but we find such a scenario inadequate to reproduce the observations. The much more likely explanation-but one which still requires more quantitative development-involves macroscopic particles escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury in size. The particles could take the form of micron-sized pyroxene or aluminum oxide dust grains. The planetary surface is hot enough to sublimate and create a high-Z atmosphere; this atmosphere may be loaded with dust via cloud condensation or explosive volcanism. Atmospheric gas escapes the planet via a Parkertype thermal wind, dragging dust grains with it. We infer a mass loss rate from the observations of order 1 M ⊕ /Gyr, with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1M ⊕ planet (twice the mass of Mercury), the evaporation timescale may be ∼0.2 Gyr. Smaller mass planets are disfavored because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail.

High-Speed Photometry of the Disintegrating Planetesimals at Wd1145+017: Evidence for Rapid Dynamical Evolution

“…In all three cases, the long egress was interpreted as a comet-like tail trailing the transiting object (Rappaport et al 2012;Budaj 2013;Vanderburg et al 2015).…”

Variability in the super-Earth 55 Cnc e

“…Recent inferences of disintegrating exo-mercuries in close-in orbits have also used volcanic outgassing as a possible means to inject dust into the planetary atmosphere before being carried away by thermal winds (e.g. Rappaport et al 2012Rappaport et al , 2014. However, whereas extremely small planets (nearly Mercury-size) subject to intense irradiation can undergo substantial mass loss through thermal winds, super-Earths are unlikely to undergo such mass-loss due to their significantly deeper potential wells (Perez-Becker & Chiang 2013;Rappaport et al 2014).…”

Drifting asteroid fragments around WD 1145+017

“…Higher cadence ground-based follow-up photometry revealed several sets of asymmetric transits with varying depths (of up to 40%) at an orbital period of ≈ 4.5 hours, but with highly inconsistent transit times . Asymmetric transit shapes and variable transit depths have come to be associated with disintegrating planets transiting main sequence stars (Rappaport 2012(Rappaport , 2014Sanchis-Ojeda 2015), and Vanderburg et al (2015) interpreted the observations of WD 1145+017 as being caused by a similar phenomenon. Vanderburg et al (2015) showed that a dust cloud formed from material sublimated off several fragments of a large, tidally disrupted asteroid (with roughly the mass of Ceres) occulting the star could plausibly explain the observed transits.…”