Vol. 572
In section 10. Planets and planetary systems

Dusty tails of evaporating exoplanets. I. Constraints on the dust composition

by R. van Lieshout, M. Min, and C. Dominik A&A 572, A76


Two small evaporating exoplanets, KIC 12557548b and the recent KOI-2700b, were discovered by the Kepler mission from their variable transit lightcurves. Lieshout et al. model the structure of the comet-like tails and that of their grains to understand the amount and nature of the material lost. In order to constrain the composition of the micron-sized grains in the tails, they use the information available from these light curves, the size of grains required to scatter the starlight appropriately, and the length of the tails to model the thermal properties of rocky materials with standard compositions. Many compositions are ruled out (e.g., some grains would have to be too large in order to avoid being evaporated and explain the entire tail), leaving out as possible solutions only the most refractory materials (corundum, Al2O3, or iron-rich silicate minerals such as Fayalite, Fe2SiO4). These planets may thus have lost their more volatile elements in a first phase and now be slowly losing the most refractory material. The discovery of other examples of these rare evaporating planets combined with spectroscopic observations of their tails could help us to determine directly the interior structure of close-in planets.