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Register a new userDetection of an Atmosphere on a Rocky Exoplanet
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We report the detection of an atmosphere on a rocky exoplanet, GJ 1132 b, which is similar to Earth in terms of size and density. The atmospheric transmission spectrum was detected using Hubble WFC3 measurements and shows spectral signatures of aerosol scattering, HCN, and CH$_{4}$ in a low mean molecular weight atmosphere. We model the atmospheric loss process and conclude that GJ 1132 b likely lost the original H/He envelope, suggesting that the atmosphere that we detect has been reestablished. We explore the possibility of H$_{2}$ mantle degassing, previously identified as a possibility for this planet by theoretical studies, and find that outgassing from ultrareduced magma could produce the observed atmosphere. In this way we use the observed exoplanet transmission spectrum to gain insights into magma composition for a terrestrial planet. The detection of an atmosphere on this rocky planet raises the possibility that the numerous powerfully irradiated Super-Earth planets, believed to be the evaporated cores of Sub-Neptunes, may, under favorable circumstances, host detectable atmospheres.
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Formation of hazes at microbar pressures has been explored by theoretical models of exoplanet atmospheres to explain Rayleigh scattering and/or featureless transmission spectra, however observational evidence of aerosols in the low pressure formation environments has proved elusive. Here, we show direct evidence of aerosols existing at $sim$1 microbar pressures in the atmosphere of the warm sub-Saturn WASP-69b using observations taken with Space Telescope Imaging Spectrograph (STIS) and Wide Field Camera 3 (WFC3) instruments on the Hubble Space Telescope. The transmission spectrum shows a wavelength-dependent slope induced by aerosol scattering that covers 11 scale heights of spectral modulation. Drawing on the extensive studies of haze in our Solar System, we model the transmission spectrum based on a scaled version of Jupiters haze density profile to show that WASP-69b transmission spectrum can be produced by scattering from an approximately constant density of particles extending throughout the atmospheric column from 40 millibar to microbar pressures. These results are consistent with theoretical expectations based on microphysics of the aerosol particles that have suggested haze can exist at microbar pressures in exoplanet atmospheres.
Recent exoplanet statistics indicate that photo-evaporation has a great impact on the mass and bulk composition of close-in low-mass planets. While there are many studies addressing photo-evaporation of hydrogen-rich or water-rich atmospheres, no detailed investigation regarding rocky vapor atmospheres (or mineral atmospheres) has been conducted. Here, we develop a new 1-D hydrodynamic model of the UV-irradiated mineral atmosphere composed of Na, Mg, O, Si, their ions and electrons, includin molecular diffusion, thermal conduction, photo-/thermo-chemistry, X--ray and UV heating, and radiative line cooling (i.e., the effects of the optical thickness and non-LTE). The focus of this paper is on describing our methodology but presents some new findings. Our hydrodynamic simulations demonstrate that almost all of the incident X-ray and UV energy from the host-star is converted into and lost by the radiative emission of the coolant gas species such as Na, Mg, Mg$^+$, Si$^{2+}$, Na$^{3+}$ and Si$^{3+}$. 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 $1 times 10^{-3}$, which corresponds to 0.3~$Mearth$/Gyr 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 $1Mearth$ 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.
Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres. Searches for helium, however, have hitherto been unsuccessful. Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near- infrared transmission spectrum of the warm gas giant WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms. The amplitude of the feature, in transit depth, is 0.049 +/- 0.011 per cent in a bandpass of 98 angstroms, which is more than five times greater than what could be caused by nominal stellar chromospheric activity. This large absorption signal suggests that WASP-107b has an extended atmosphere that is eroding at a total rate of 10^10 to 3 x 10^11 grams per second (0.1-4 per cent of its total mass per billion years), and may have a comet-like tail of gas shaped by radiation pressure.
We present a primary transit observation for the ultra hot (Teq~2400K) gas giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field Camera 3 in spectroscopic mode across the 1.12-1.64 micron wavelength range. The 1.4 micron water absorption band is detected at high confidence (5.4 sigma) in the planetary atmosphere. We also reanalyze ground-based photometric lightcurves taken in the B, r, and z filters. Significantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. We conclude that scattering by high-altitude haze alone is unlikely to account for this difference, and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. Enhanced opacity is also inferred across the 1.12-1.3 micron wavelength range, possibly due to iron hydride absorption. If confirmed, WASP-121b will be the first exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. The latter are important species in M/L dwarfs, and their presence is likely to have a significant effect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversion.
Most known terrestrial planets orbit small stars with radii less than 60% that of the Sun. Theoretical models predict that these planets are more vulnerable to atmospheric loss than their counterparts orbiting Sun-like stars. To determine whether a thick atmosphere has survived on a small planet, one approach is to search for signatures of atmospheric heat redistribution in its thermal phase curve. Previous phase curve observations of the super-Earth 55 Cancri e (1.9 Earth radii) showed that its peak brightness is offset from the substellar point $-$ possibly indicative of atmospheric circulation. Here we report a phase curve measurement for the smaller, cooler planet LHS 3844b, a 1.3 Earth radius world in an 11-hour orbit around a small, nearby star. The observed phase variation is symmetric and has a large amplitude, implying a dayside brightness temperature of $1040pm40$ kelvin and a nightside temperature consistent with zero kelvin (at one standard deviation). Thick atmospheres with surface pressures above 10 bar are ruled out by the data (at three standard deviations), and less-massive atmospheres are unstable to erosion by stellar wind. The data are well fitted by a bare rock model with a low Bond albedo (lower than 0.2 at two standard deviations). These results support theoretical predictions that hot terrestrial planets orbiting small stars may not retain substantial atmospheres.
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