We find most features are still detectable for transit depths of ∼0.3% in the visible range. The detectability of compositional features is easier with an average grain size of 1 μm despite features being more prominent with smaller grain sizes. For the average transit depth of 0.55% in the Kepler band for K2-22b, the features in the transmission spectra can be as large as 1%, which is detectable with the James Webb Space Telescope (JWST) MIRI low-resolution spectrograph in a single transit. We find that silicate resonant features near 10 μm can produce transit depths that are at least as large as those in the visible. To assess the ability of such observations to diagnose the dust composition, we simulate the transmission spectra from 5 to 14 μm for the planet tail assuming an optically thin dust cloud comprising a single dust species with a constant column density scaled to yield a chosen visible transit depth. Their transit signal is dominated by dusty effluents forming a comet-like tail trailing the host planet (or leading it, in the case of K2-22b), making these good candidates for transmission spectroscopy. This provides a unique opportunity to probe to interior composition of the smallest known exoplanets.ĭisintegrating planets allow for the unique opportunity to study the composition of the interiors of small, hot, rocky exoplanets because the interior is evaporating and that material is condensing into dust, which is being blown away and then transiting the star.
Using a detailed, physically motivated model, it is possible to constrain the composition of the dust in the tails of evaporating rocky exoplanets. These constraints are consistent with dust made of corundum (Al2O3), but do not agree with a range of carbonaceous, silicate, or iron compositions. We find that only certain combinations of material parameters yield the correct tail length. Good fits are found for initial grain sizes between 0.2 and 5.6 micron and dust mass loss rates of 0.6 to 15.6 M_earth/Gyr (2-sigma ranges). Our physics-based model is capable of reproducing the observed light curve in detail. We explore the free-parameter space thoroughly using a Markov chain Monte Carlo method. From this dust cloud shape, we generate synthetic light curves (incorporating the effects of extinction and angle-dependent scattering), which are then compared with the phase-folded Kepler light curve. Using a self-consistent numerical model of the dust dynamics and sublimation, we calculate the shape of the tail by following dust grains from their ejection from the planet to their destruction due to sublimation. We aim to use the detailed shape of the Kepler light curve of KIC 12557548b to constrain the size and composition of the dust grains that make up the tail, as well as the mass loss rate of the planet. When such objects occult their host star, the resulting transit signal contains information about the dust in the tail. Evaporating rocky exoplanets, such as KIC 12557548b, eject large amounts of dust grains, which can trail the planet in a comet-like tail.
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