Motivated by recent detection of transiting high-density super-Earths, we explore the detectability of hot rocky super-Earths orbiting very close to their host stars. In the environment hot enough for their rocky surfaces to be molten, they would have the atmosphere composed of gas species from the magma oceans. In this study, we investigate the radiative properties of the atmosphere that is in the gas/melt equilibrium with the underlying magma ocean. Our equilibrium calculations yield Na, K, Fe, Si, SiO, O, and O 2 as the major atmospheric species. We compile the radiative-absorption line data of those species available in literature, and calculate their absorption opacities in the wavelength region of 0.1-100 µm. Using them, we integrate the thermal structure of the atmosphere. Then, we find that thermal inversion occurs in the atmosphere because of the UV absorption by SiO. In addition, we calculate the ratio of the planetary to stellar emission fluxes during secondary eclipse, and find prominent emission features induced by SiO at 4 µm detectable by Spitzer, and those at 10 and 100 µm detectable by near-future space telescopes.

Violent variation of transit depths and an ingress-egress asymmetry of the transit light curve discovered in KIC 12557548 have been interpreted as evidences of a catastrophic evaporation of atmosphere with dust (Ṁ p 1M ⊕ Gyr −1 ) from a close-in small planet. To explore what drives the anomalous atmospheric escape, we perform time-series analysis of the transit depth variation of Kepler archival data for ∼ 3.5 yr. We find a ∼ 30% periodic variation of the transit depth with P 1 = 22.83 ± 0.21 days, which is within the error of the rotation period of the host star estimated using the light curve modulation, P rot = 22.91 ± 0.24 days. We interpret the results as evidence that the atmospheric escape of KIC 12557548b correlates with stellar activity. We consider possible scenarios that account for both the mass loss rate and the correlation with stellar activity. X-ray and ultraviolet (XUV)-driven evaporation is possible if one accepts a relatively high XUV flux and a high efficiency for converting the input energy to the kinetic energy of the atmosphere. Star-planet magnetic interaction is another possible scenario though huge uncertainty remains for the mass loss rate.

We have undertaken a search for the infrared emission from the intracluster dust in the Coma cluster of galaxies by the Multiband Imaging Photometer for Spitzer. Our observations yield the deepest mid and far-infrared images of a galaxy cluster ever achieved. In each of the three bands, we have not detected a signature of the central excess component in contrast to the previous report on the detection by Infrared Space Observatory (ISO). We still find that the brightness ratio between 70µm and 160µm shows a marginal sign of the central excess, in qualitative agreement with the ISO result. Our analysis suggests that the excess ratio is more likely due to faint infrared sources lying on fluctuating cirrus foreground. Our observations yield the 2σ upper limits on the excess emission within 100 kpc of the cluster center as 5 × 10 −3 MJy/sr, 6 × 10 −2 MJy/sr, and 7 × 10 −2 MJy/sr, at 24, 70, and 160 µm, respectively. These values are in agreement with those found in other galaxy clusters and suggest that dust is deficient near the cluster center by more than 3 orders of magnitude compared to the interstellar medium.

Recent exoplanet statistics indicate that photo-evaporation has a great impact on the mass and bulk composition of close-in low-mass planets. While there are many studies addressing photo-evaporation of hydrogen- or water-rich atmospheres, no detailed investigation regarding rocky vapour atmospheres (or mineral atmospheres) has been conducted. Here, we develop a new 1D hydrodynamic model of the ultraviolet (UV)-irradiated mineral atmosphere composed of Na, Mg, O, Si, their ions and electrons, including molecular diffusion, thermal conduction, photo-/thermochemistry, X–ray and UV heating, and radiative line cooling (i.e. the effects of the optical thickness and non-local thermal equilibrium). The focus of this paper is on describing our methodology but presents some new findings. Our hydrodynamic simulations demonstrate that almost all of the incident X-ray and UV energy from the host star is converted into and lost by the radiative emission of the coolant gas species such as Na, Mg, Mg+, Si2+, Na3+, and Si3+. For an Earth-size planet orbiting 0.02 au around a young solar-type star, we find that the X-ray and UV heating efficiency is as small as 1 × 10−3, which corresponds to 0.3 M⊕ Gyr−1 of the mass-loss rate simply integrated over all the directions. Because of such efficient cooling, the photo-evaporation of the mineral atmosphere on hot rocky exoplanets with masses of 1 M⊕ is not massive enough to exert a great influence on the planetary mass and bulk composition. This suggests that close-in high-density exoplanets with sizes larger than the Earth radius survive in the high-UV environments.