Showing papers by "Julianne I. Moses published in 2014"
TL;DR: This work reviews the two key mechanisms by which kinetic processes drive an exoplanet atmosphere out of equilibrium are photochemistry and transport-induced quenching and examines some of the current evidence for kinetic processes on extrasolar planets.
Abstract: Chemical kinetics plays an important role in controlling the atmospheric composition of all planetary atmospheres, including those of extrasolar planets. For the hottest exoplanets, the composition can closely follow thermochemical-equilibrium predictions, at least in the visible and infrared photosphere at dayside (eclipse) conditions. However, for atmospheric temperatures , and in the uppermost atmosphere at any temperature, chemical kinetics matters. The two key mechanisms by which kinetic processes drive an exoplanet atmosphere out of equilibrium are photochemistry and transport-induced quenching. I review these disequilibrium processes in detail, discuss observational consequences and examine some of the current evidence for kinetic processes on extrasolar planets.
119 citations
University College London1, Planetary Science Institute2, European Space Agency3, Queen Mary University of London4, University of Leicester5, Lancaster University6, University of Wisconsin-Madison7, Jet Propulsion Laboratory8, Cornell University9, Centre national de la recherche scientifique10, University of Grenoble11, Rutherford Appleton Laboratory12, Braunschweig University of Technology13, Delft University of Technology14, University of Liège15, Maynooth University16, Johns Hopkins University Applied Physics Laboratory17, University of Orléans18, Max Planck Society19, Goddard Space Flight Center20, National and Kapodistrian University of Athens21, University of California, Berkeley22, Southwest Research Institute23, Imperial College London24, INAF25, University of Oxford26, University of California, Santa Cruz27, University of Colorado Boulder28, University of Idaho29, Tel Aviv University30, Heidelberg University31, University of Liverpool32, University of Iowa33, University of Southampton34, Royal Observatory of Belgium35, University of Stuttgart36, Bundeswehr University Munich37, university of lille38, Institut de Physique du Globe de Paris39, University of Vienna40, Austrian Academy of Sciences41, National University of Ireland42, Space Science Institute43, University of Cologne44, Université de Namur45, University of Reading46, Pierre-and-Marie-Curie University47, University of California, Los Angeles48, University of the Basque Country49, University of Virginia50, Lunar and Planetary Institute51, Academy of Athens52, University of Potsdam53, International Space Science Institute54, University of Nantes55
TL;DR: In this article, the authors describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus' atmosphere, and discuss the technical challenges for such a mission.
75 citations
TL;DR: In this article, mid-infrared spectral observations from the Spitzer Space Telescope were used to determine the abundances of C 2 H 2 and CO 2 on Uranus at the time of the 2007 equinox.
72 citations
TL;DR: In this paper, a broad-band spectrum of the disk of Uranus was obtained from the Spitzer Infrared Spectrometer (IRS) ten days after the planet's equinox, when its equator was close to the sub-Earth point.
71 citations
TL;DR: In this paper, high-resolution photoabsorption cross sections for the H2 bands were used to predict a broad region of hydrocarbon ions that is below the main peak and is produced by absorption of solar photons in the wavelength range 842 to 1116 A, which penetrate to altitudes below the methane homopause.
Abstract: [1] Radio occultation measurements of the Saturn ionosphere have shown that persistent but variable electron density layers appear well below the major peaks. We model here the region of hydrocarbon ions that is below the main peak and is produced by absorption of solar photons in the wavelength range 842 to 1116 A, which penetrate to altitudes below the methane homopause in the wings of the H2 absorption lines, and in the gaps between groups of lines. In this wavelength range, H2 absorbs photons in discrete transitions to rovibrational levels of electronically excited states, which then decay to a range of rovibrational levels of the electronic ground state, or to the continuum of the ground state. The cross sections for these discrete absorptions vary by several orders of magnitude from the peaks to the wings of the absorption lines. We find that the adoption of high resolution photoabsorption cross sections for the H2 bands leads to different photoionization profiles for both the hydrocarbons and H atoms, and to peak inline imagephotoproduction profiles that are more than an order of magnitude larger than those computed with low resolution cross sections. For the present model, we find that ionization by energetic electrons that accompany the absorption of soft X-rays appears in the same altitude range. We predict that a broad region of hydrocarbon ions appears well below the main peak, in the altitude range 600 to 1000 km above the 1 bar level (2–0.04 μbar) with a maximum electron density of ∼3×103cm−3 at low solar activity.
33 citations
TL;DR: In this paper, the authors used the most updated radiative transfer programs to construct a 3-μm emission model of CH 4 to be compared with the ISO data, and derived the high-altitude CH 4 mixing ratios, which turn out to be at least 10 times smaller than the microbar CH4 mixing ratios assumed in the Galileo probe analysis.
14 citations
TL;DR: Hubble Space Telescope observations of two separate sub-Jupiter-sized extrasolar planets shed light on the properties of their atmospheres, with Heather Knutson and Laura Kreidberg arguing that their near-infrared spectra are consistent with the presence of high-altitude clouds that obscure the lower layers of GJ 1214b.
Abstract: The flat and featureless transmission spectra of two intermediate-sized extrasolar planets, observed during the planets' passage across their host stars, shed light on the properties of their atmospheres. See Letters p.66
& p.69
Two papers in this issue of Nature report Hubble Space Telescope observations of two separate sub-Jupiter-sized extrasolar planets. Heather Knutson et al. observed four transits of the Neptune-mass planet GJ 436b and Laura Kreidberg et al. observed 15 transits of the smaller 'super-Earth' GJ 1214b. The transmission spectra of starlight passing through the atmospheres of these planets should give a good indication of the nature of their respective atmospheres, and for both planets the spectra obtained from Hubble's Wide Field Camera 3 are virtually featureless. Knutson et al. argue that their data are consistent with either a high cloud deck at pressures of 0.1–10 mbar or a hydrogen-poor atmosphere on GJ 436b. Kreidberg et al. conclude that their near-infrared spectra are consistent with the presence of high-altitude clouds that obscure the lower layers of GJ 1214b.
4 citations