Björn Benneke

Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b.

Recent surveys have revealed that planets intermediate in size between Earth and Neptune (‘super-Earths’) are among the most common planets in the Galaxy. Atmospheric studies are the next step towards developing a comprehensive understanding of this new class of object. Much effort has been focused on using transmission spectroscopy to characterize the atmosphere of the super-Earth archetype GJ 1214b (refs 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17), but previous observations did not have sufficient precision to distinguish between two interpretations for the atmosphere. The planet’s atmosphere could be dominated by relatively heavy molecules, such as water (for example, a 100 per cent water vapour composition), or it could contain high-altitude clouds that obscure its lower layers. Here we report a measurement of the transmission spectrum of GJ 1214b at near-infrared wavelengths that definitively resolves this ambiguity. The data, obtained with the Hubble Space Telescope, are sufficiently precise to detect absorption features from a high mean-molecular-mass atmosphere. The observed spectrum, however, is featureless. We rule out cloud-free atmospheric models with compositions dominated by water, methane, carbon monoxide, nitrogen or carbon dioxide at greater than 5σ confidence. The planet’s atmosphere must contain clouds to be consistent with the data.

A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b

GJ 436b is a warm—approximately 800 kelvin—exoplanet that periodically eclipses its low-mass (half the mass of the Sun) host star, and is one of the few Neptune-mass planets that is amenable to detailed characterization. Previous observations have indicated that its atmosphere has a ratio of methane to carbon monoxide that is 105 times smaller than predicted by models for hydrogen-dominated atmospheres at these temperatures. A recent study proposed that this unusual chemistry could be explained if the planet’s atmosphere is significantly enhanced in elements heavier than hydrogen and helium. Here we report observations of GJ 436b’s atmosphere obtained during transit. The data indicate that the planet’s transmission spectrum is featureless, ruling out cloud-free, hydrogen-dominated atmosphere models with an extremely high significance of 48σ. The measured spectrum is consistent with either a layer of high cloud located at a pressure level of approximately one millibar or with a relatively hydrogen-poor (three per cent hydrogen and helium mass fraction) atmospheric composition.

Detection of a transit of the super-Earth 55 Cancri e with warm Spitzer

We report on the detection of a transit of the super-Earth 55 Cnc e with warm Spitzer in IRAC’s 4.5 μm band. Our MCMC analysis includes an extensive modeling of the systematic effects affecting warm Spitzer photometry, and yields a transit depth of 410±63 ppm, which translates to a planetary radius of 2.08 +0.16 −0.17 R⊕ as measured in IRAC 4.5 μm channel. A planetary mass of 7.81 +0.58 −0.53 M⊕ is derived from an extensive set of radial-velocity data, yielding a mean planetary density of 4.78 +1.31 −1.20 gc m −3 . Thanks to the brightness of its host star (V = 6, K = 4), 55 Cnc e is a unique target for the thorough characterization of a super-Earth orbiting around a solar-type star.

Improved precision on the radius of the nearby super-Earth 55 Cnc e

We report on new transit photometry for the super-Earth 55 Cnc e obtained with Warm Spitzer/IRAC at 4.5µm. An individual analysis of these new data leads to a planet radius of 2.21 +0.15 −0.16 R⊕, in good agreement with the values previously derived from the MOST and Spitzer transit discovery data. A global analysis of both Spitzer transit time-series improves the precision on the radius of the planet at 4.5µm to 2.20± 0.12 R⊕. We also performed an independent analysis of the MOST data, paying particular attention to the influence of the systematic effects of instrumental origin on the derived parameters and errors by including them in a global model instead of performing a preliminary detrending-filtering processing . We deduce from this reanalysis of MOST data an optical planet radius of 2.04± 0.15 R⊕ that is consistent with our Spitzer infrared radius. Assuming the achromaticity of the transit depth, we performed a global analysis combining Spitzer and MOST data that results in a planet radius of 2.17± 0.10 R⊕ (13, 820± 620 km). These results confirm that the most probable composition of 55 Cnc e is an env elope of supercritical water above a rocky nucleus.

A map of the large day–night temperature gradient of a super-Earth exoplanet

Over the past decade, observations of giant exoplanets (Jupiter-size) have provided key insights into their atmospheres, but the properties of lower-mass exoplanets (sub-Neptune) remain largely unconstrained because of the challenges of observing small planets. Numerous efforts to observe the spectra of super-Earths—exoplanets with masses of one to ten times that of Earth—have so far revealed only featureless spectra. Here we report a longitudinal thermal brightness map of the nearby transiting super-Earth 55 Cancri e (refs 4, 5) revealing highly asymmetric dayside thermal emission and a strong day–night temperature contrast. Dedicated space-based monitoring of the planet in the infrared revealed a modulation of the thermal flux as 55 Cancri e revolves around its star in a tidally locked configuration. These observations reveal a hot spot that is located 41 ± 12 degrees east of the substellar point (the point at which incident light from the star is perpendicular to the surface of the planet). From the orbital phase curve, we also constrain the nightside brightness temperature of the planet to 1,380 ± 400 kelvin and the temperature of the warmest hemisphere (centred on the hot spot) to be about 1,300 kelvin hotter (2,700 ± 270 kelvin) at a wavelength of 4.5 micrometres, which indicates inefficient heat redistribution from the dayside to the nightside. Our observations are consistent with either an optically thick atmosphere with heat recirculation confined to the planetary dayside, or a planet devoid of atmosphere with low-viscosity magma flows at the surface.

197 CANDIDATES AND 104 VALIDATED PLANETS IN K2's FIRST FIVE FIELDS

NASA through the Sagan Fellowship Program; NASA through a Hubble Fellowship - Space Telescope Science Institute; NASA [NAS 5-26555, NNH14CK55B]; National Science Foundation Graduate Research Fellowship [2014184874]; FONDECYT [1130857]; BASAL CATA [PFB-06]; Ministry for the Economy, Development, and Tourisms Programa Iniciativa Cientifica Milenio [IC 120009]; Alfred P. Sloan Foundation; National Science Foundation [AST-0906060, AST-0960343, AST-1207891]; Mt. Cuba Astronomical Foundation; Max Planck Institute for Astronomy; Heidelberg; Max Planck Institute for Extraterrestrial Physics, Garching; Johns Hopkins University; Durham University; University of Edinburgh; Queens University Belfast; Harvard-Smithsonian Center for Astrophysics; Las Cumbres Observatory Global Telescope Network Incorporated; National Central University of Taiwan; Space Telescope Science Institute; National Aeronautics and Space Administration [NNX08AR22G]; University of Maryland; Eotvos Lorand University (ELTE)

Observing Exoplanets with High Dispersion Coronagraphy. I. The Scientific Potential of Current and Next-generation Large Ground and Space Telescopes

Direct imaging of exoplanets presents a formidable technical challenge owing to the small angular separation and high contrast between exoplanets and their host stars. High Dispersion Coronagraphy (HDC) is a pathway to achieve unprecedented sensitivity to Earth-like planets in the habitable zone. Here, we present a framework to simulate HDC observations and data analyses. The goal of these simulations is to perform a detailed analysis of the trade-off between raw star light suppression and spectral resolution for various instrument configurations, target types, and science cases. We predict the performance of an HDC instrument at Keck observatory for characterizing directly imaged gas-giant planets in near infrared bands. We also simulate HDC observations of an Earth-like planet using next-generation ground-based (TMT) and spaced-base telescopes (HabEx and LUVOIR). We conclude that ground-based ELTs are more suitable for HDC observations of an Earth-like planet than future space-based missions owing to the considerable difference in collecting area. For ground-based telescopes, HDC observations can detect an Earth-like planet in the habitable zone around an M dwarf star at 10

Hubble Space Telescope search for the transit of the Earth-mass exoplanet α Centauri B b

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HAT-P-26b: A Neptune-mass exoplanet with a well-constrained heavy element abundance

starlight suppression level. Compared to the 10

Spitzer Observations Confirm and Rescue the Habitable-zone Super-Earth K2-18b for Future Characterization

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