ALBERT

Description: 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 - 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 5sigma confidence. The planet's atmosphere must contain clouds to be consistent with the data.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kreidberg, Laura -- Bean, Jacob L -- Desert, Jean-Michel -- Benneke, Bjorn -- Deming, Drake -- Stevenson, Kevin B -- Seager, Sara -- Berta-Thompson, Zachory -- Seifahrt, Andreas -- Homeier, Derek -- England -- Nature. 2014 Jan 2;505(7481):69-72. doi: 10.1038/nature12888.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Astronomy and Astrophysics, University of Chicago, Chicago, Illinois 60637, USA. ; 1] CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80309, USA [2] Department of Astronomy, California Institute of Technology, Pasadena, California 91101, USA. ; Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ; Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA. ; 1] Department of Astronomy, Harvard University, Cambridge, Massachusetts 02138, USA [2] MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ; Centre de Recherche Astrophysique de Lyon, 69364 Lyon, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24380954" target="_blank"〉PubMed〈/a〉

Description: 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 10(5) 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 48sigma. 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Knutson, Heather A -- Benneke, Bjorn -- Deming, Drake -- Homeier, Derek -- England -- Nature. 2014 Jan 2;505(7481):66-8. doi: 10.1038/nature12887.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. ; 1] Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA [2] Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ; Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA. ; Centre de Recherche Astrophysique de Lyon, 69364 Lyon, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24380953" target="_blank"〉PubMed〈/a〉

Description: Transmission spectroscopy has so far detected atomic and molecular absorption in Jupiter-sized exoplanets, but intense efforts to measure molecular absorption in the atmospheres of smaller (Neptune-sized) planets during transits have revealed only featureless spectra. From this it was concluded that the majority of small, warm planets evolve to sustain atmospheres with high mean molecular weights (little hydrogen), opaque clouds or scattering hazes, reducing our ability to observe the composition of these atmospheres. Here we report observations of the transmission spectrum of the exoplanet HAT-P-11b (which has a radius about four times that of Earth) from the optical wavelength range to the infrared. We detected water vapour absorption at a wavelength of 1.4 micrometres. The amplitude of the water absorption (approximately 250 parts per million) indicates that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar, and sufficiently rich in hydrogen to have a large scale height (over which the atmospheric pressure varies by a factor of e). The spectrum is indicative of a planetary atmosphere in which the abundance of heavy elements is no greater than about 700 times the solar value. This is in good agreement with the core-accretion theory of planet formation, in which a gas giant planet acquires its atmosphere by accreting hydrogen-rich gas directly from the protoplanetary nebula onto a large rocky or icy core.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fraine, Jonathan -- Deming, Drake -- Benneke, Bjorn -- Knutson, Heather -- Jordan, Andres -- Espinoza, Nestor -- Madhusudhan, Nikku -- Wilkins, Ashlee -- Todorov, Kamen -- England -- Nature. 2014 Sep 25;513(7519):526-9. doi: 10.1038/nature13785.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Department of Astronomy, University of Maryland, College Park, Maryland 20742-2421, USA [2] Instituto de Astrofisica, Pontificia Universidad Catolica de Chile, 7820436 Macul, Santiago, Chile [3] Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. ; 1] Department of Astronomy, University of Maryland, College Park, Maryland 20742-2421, USA [2] NASA Astrobiology Institute's Virtual Planetary Laboratory, Seattle, Washington 98195, USA. ; Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. ; Instituto de Astrofisica, Pontificia Universidad Catolica de Chile, 7820436 Macul, Santiago, Chile. ; Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK. ; Department of Astronomy, University of Maryland, College Park, Maryland 20742-2421, USA. ; Department of Physics, ETH Zurich, 8049 Zurich, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25254473" target="_blank"〉PubMed〈/a〉

Description: 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Demory, Brice-Olivier -- Gillon, Michael -- de Wit, Julien -- Madhusudhan, Nikku -- Bolmont, Emeline -- Heng, Kevin -- Kataria, Tiffany -- Lewis, Nikole -- Hu, Renyu -- Krick, Jessica -- Stamenkovic, Vlada -- Benneke, Bjorn -- Kane, Stephen -- Queloz, Didier -- England -- Nature. 2016 Apr 14;532(7598):207-9. doi: 10.1038/nature17169. Epub 2016 Mar 30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK. ; Institut d'Astrophysique et de Geophysique, Universite of Liege, allee du 6 Aout 17, 4000 Liege, Belgium. ; Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA. ; Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK. ; NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium. ; University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012, Bern, Switzerland. ; Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK. ; Space Telescope Science Institute, Baltimore, Maryland 21218, USA. ; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. ; Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. ; Spitzer Science Center, MS 220-6, California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California 91125, USA. ; Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 94132, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27027283" target="_blank"〉PubMed〈/a〉

Description: Results from exoplanet surveys indicate that small planets (super-Earth size and below) are abundant in our Galaxy. However, little is known about their interiors and atmospheres. There is therefore a need to find small planets transiting bright stars, which would enable a detailed characterization of this population of objects. We present the results of a search for the transit of the Earth-mass exoplanet α Centauri B b with the Hubble Space Telescope ( HST ). We observed α Centauri B twice in 2013 and 2014 for a total of 40 h. We achieve a precision of 115 ppm per 6-s exposure time in a highly saturated regime, which is found to be consistent across HST orbits. We rule out the transiting nature of α Centauri B b with the orbital parameters published in the literature at 96.6 per cent confidence. We find in our data a single transit-like event that could be associated with another Earth-sized planet in the system, on a longer period orbit. Our programme demonstrates the ability of HST to obtain consistent, high-precision photometry of saturated stars over 26 h of continuous observations.

Description: A correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own Solar System and has served as a cornerstone of planet-formation theory. Using data from the Hubble and Spitzer Space Telescopes from 0.5 to 5 micrometers, we conducted a detailed atmospheric study of the transiting Neptune-mass exoplanet HAT-P-26b. We detected prominent H 2 O absorption bands with a maximum base-to-peak amplitude of 525 parts per million in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b’s atmospheric heavy element content ( 4.8–4.0+21.5 times solar). This likely indicates that HAT-P-26b’s atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals.

Description: Orbiting a bright, nearby star the 55 Cnc system offers a rare opportunity to study a multiplanet system that has a wide range of planetary masses and orbital distances. Using two decades of photometry and spectroscopy data, we have measured the rotation of the host star and its solar-like magnetic cycle. Accounting for this cycle in our velocimetric analysis of the system allows us to revise the properties of the outermost giant planet and its four planetary companions. The innermost planet 55 Cnc e is an unusually close-in super-Earth, whose transits have allowed for detailed follow-up studies. Recent observations favor the presence of a substantial atmosphere yet its composition, and the nature of the planet, remain unknown. We combined our derived planet mass (Mp = 8.0 ± 0.3 MEarth) with refined measurement of its optical radius derived from HST/STIS observations (Rp = 1.88 ± 0.03 REarth over 530–750 nm) to revise the density of 55 Cnc e (ρ = 6.7 ± 0.4 g cm−3). Based on these revised properties we have characterized possible interiors of 55 Cnc e using a generalized Bayesian model. We confirm that the planet is likely surrounded by a heavyweight atmosphere, contributing a few percents of the planet radius. While we cannot exclude the presence of a water layer underneath the atmosphere, this scenario is unlikely given the observations of the planet across the entire spectrum and its strong irradiation. Follow-up observations of the system in photometry and in spectroscopy over different time-scales are needed to further investigate the nature and origin of this iconic super-Earth.