19 research outputs found
A ground-based transmission spectrum of the super-Earth exoplanet GJ 1214b
No full textIn contrast to planets with masses similar to that of Jupiter and higher, the bulk compositions of planets in the so-called super-Earth regime (masses 2-10 times that of the Earth) cannot be uniquely determined from a measurement of mass and radius alone. For these planets, there is a degeneracy between the mass and composition of both the interior and a possible atmosphere in theoretical models(1,2). The recently discovered transiting super-Earth exoplanet GJ 1214b is one example of this problem(3). Three distinct models for the planet that are consistent with its mass and radius have been suggested(4). Breaking the degeneracy between these models requires obtaining constraints on the planet's atmospheric composition(5,6). Here we report a ground-based measurement of the transmission spectrum of GJ 1214b between wavelengths of 780 and 1,000 nm. The lack of features in this spectrum rules out (at 4.9 sigma confidence) cloud-free atmospheres composed primarily of hydrogen. If the planet's atmosphere is hydrogen-dominated, then it must contain clouds or hazes that are optically thick at the observed wavelengths at pressures less than 200 mbar. Alternatively, the featureless transmission spectrum is also consistent with the presence of a dense, water vapour atmosphere.European Commissions; NAS
THE FLAT TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ1214b FROM WIDE FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE
No full textCapitalizing on the observational advantage offered by its tiny M dwarf host, we present Hubble Space Telescope/Wide Field Camera 3 (WFC3) grism measurements of the transmission spectrum of the super-Earth exoplanet GJ1214b. These are the first published WFC3 observations of a transiting exoplanet atmosphere. After correcting for a ramp-like instrumental systematic, we achieve nearly photon-limited precision in these observations, finding the transmission spectrum of GJ1214b to be flat between 1.1 and 1.7 mu m. Inconsistent with a cloud-free solar composition atmosphere at 8.2 sigma, the measured achromatic transit depth most likely implies a large mean molecular weight for GJ1214b's outer envelope. A dense atmosphere rules out bulk compositions for GJ1214b that explain its large radius by the presence of a very low density gas layer surrounding the planet. High-altitude clouds can alternatively explain the flat transmission spectrum, but they would need to be optically thick up to 10 mbar or consist of particles with a range of sizes approaching 1 mu m in diameter
BROADBAND TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH GJ 1214b SUGGESTS A LOW MEAN MOLECULAR WEIGHT ATMOSPHERE
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The Flat Transmission Spectrum of the Super-earth Gj1214b From Wide Field Camera 3 on the Hubble Space Telescope
No full textCapitalizing on the observational advantage offered by its tiny M dwarf host, we present Hubble Space Telescope/Wide Field Camera 3 (WFC3) grism measurements of the transmission spectrum of the super-Earth exoplanet GJ1214b. These are the first published WFC3 observations of a transiting exoplanet atmosphere. After correcting for a ramp-like instrumental systematic, we achieve nearly photon-limited precision in these observations, finding the transmission spectrum of GJ1214b to be flat between 1.1 and 1.7 mu m. Inconsistent with a cloud-free solar composition atmosphere at 8.2 sigma, the measured achromatic transit depth most likely implies a large mean molecular weight for GJ1214b's outer envelope. A dense atmosphere rules out bulk compositions for GJ1214b that explain its large radius by the presence of a very low density gas layer surrounding the planet. High-altitude clouds can alternatively explain the flat transmission spectrum, but they would need to be optically thick up to 10 mbar or consist of particles with a range of sizes approaching 1 mu m in diameter.Version of Recor
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Observational Evidence for a Metal-rich Atmosphere on the Super-earth Gj1214b
No full textWe report observations of two consecutive transits of the warm super-Earth exoplanet GJ 1214b at 3.6 and 4.5 mu m with the Infrared Array Camera instrument on board the Spitzer Space Telescope. The two transit light curves allow for the determination of the transit parameters for this system. We find these parameters to be consistent with the previously determined values and no evidence for transit timing variations. The main investigation consists of measuring the transit depths in each bandpass to constrain the planet's transmission spectrum. Fixing the system scale and impact parameters, we measure R-p/R-star = 0.1176(-0.0009)(+0.0008) and 0.1163(-0.0008)(+0.0010) at 3.6 and 4.5 mu m, respectively. Combining these data with the previously reported MEarth Observatory measurements in the red optical allows us to rule out a cloud-free, solar composition (i.e., hydrogen-dominated) atmosphere at 4.5 sigma confidence. This independently confirms a recent finding that was based on a measurement of the planet's transmission spectrum using the Very Large Telescope (VLT). The Spitzer, MEarth, and VLT observations together yield a remarkably flat transmission spectrum over the large wavelength domain spanned by the data. Consequently, cloud-free atmospheric models require more than 30% metals (assumed to be in the form of H2O) by volume to be consistent with all the observations.Version of Recor
The Optical and near-Infrared Transmission Spectrum of the Super-Earth Gj1214b: Further Evidence for a Metal-Rich Atmosphere
No full textWe present an investigation of the transmission spectrum of the 6.5 M [subscript ⊕] planet GJ 1214b based on new ground-based observations of transits of the planet in the optical and near-infrared, and on previously published data. Observations with the VLT + FORS and Magellan + MMIRS using the technique of multi-object spectroscopy with wide slits yielded new measurements of the planet's transmission spectrum from 0.61 to 0.85 μm, and in the J, H, and K atmospheric windows. We also present a new measurement based on narrow-band photometry centered at 2.09 μm with the VLT + HAWKI. We combined these data with results from a reanalysis of previously published FORS data from 0.78 to 1.00 μm using an improved data reduction algorithm, and previously reported values based on Spitzer data at 3.6 and 4.5 μm. All of the data are consistent with a featureless transmission spectrum for the planet. Our K-band data are inconsistent with the detection of spectral features at these wavelengths reported by Croll and collaborators at the level of 4.1σ. The planet's atmosphere must either have at least 70% H[subscript 2]O by mass or optically thick high-altitude clouds or haze to be consistent with the data
Optical Properties of Organic Hazes in Water-rich Exoplanet Atmospheres: Implications for Observations with JWST
No full textInternational audienceJWST has begun its scientific mission, which includes the atmospheric characterization of transiting exoplanets. Some of the first exoplanets to be observed by JWST have equilibrium temperatures below 1000 K, which is a regime where photochemical hazes are expected to form. The optical properties of these hazes, which controls how they interact with light, are critical for interpreting exoplanet observations, but relevant data are not available. Here we measure the optical properties of organic haze analogues generated in water-rich exoplanet atmosphere experiments. We report optical constants (0.4 to 28.6 μm) of organic hazes for current and future observational and modeling efforts covering the entire wavelength range of JWST instrumentation and a large part of Hubble. We use these optical constants to generate hazy model atmospheric spectra. The synthetic spectra show that differences in haze optical constants have a detectable effect on the spectra, impacting our interpretation of exoplanet observations. This study emphasizes the need to investigate the optical properties of hazes formed in different exoplanet atmospheres, and establishes a practical procedure to determine such properties
Risk conceptualisations, trust and decision-making in the face of contradictory information: the case of MMR
No full textThis thesis investigates the process by which parents evaluate contradictory information about risk in order to make the decision whether to have their children immunised with the measles, mumps and rubella (MMR) vaccine. Contested reports associating the MMR vaccine with autism have resulted in diminished confidence and uptake of the vaccine in the UK. Interviews and focus groups were used to develop an in-depth picture of parental notions of risk, trust and decision-making processes. Cultural consensus analysis was used to probe the areas of consensus and divergence of opinion, and a large-scale postal survey (N=996) assessed the level of agreement with the qualitative findings. Parental ambivalence to the safety of the vaccine reflected wider social concerns, and was crucially related to trust in governmental medical authority and medical practitioners. Trust was particularly damaged when practitioners and policy makers failed to recognise parents' concern for their children’s health and their unique knowledge of their own children. A key tool for fostering trust is narrative: this played a central role in galvanising resistance to the vaccine, but was not well used to engender trust and cooperation between parents and medical practitioners. Three practical strategies to protect children from diseases and harmful vaccine side effects, to rebuild trust, and to cope successfully with similar controversies in the future emerged from this research: fully involving the public in framing scientific research agendas, streamlining the reporting procedures for suspected adverse reactions, and fostering trusting personal relationships between patients and health care practitioners
