Planetary atmosphere observation analysis

Abstract:

Why are the terrestrial planets so different? Venus should be the most Earth-like of all our planetary neighbours. Its size, bulk composition and distance from the Sun are very similar to those of the Earth. Its original atmosphere was probably similar to that of early Earth, with large atmospheric abundances of carbon dioxide and water - possibly even a liquid water ocean. While on Earth a moderate climate ensued, Venus experienced runaway greenhouse warming, which led to its current hostile climate. How and why did it all go wrong for Venus? What lessons can we learn about the life story of terrestrial planets in general, whether in our solar system or in others? ESA's Venus Express mission proved very successful, answering many questions about Earth's sibling planet and establishing European leadership in Venus research. However, further understanding of Venus and its history requires several more lines of investigation. Entry into the atmosphere is required to measure noble gas isotopes to constrain formation & evolution models. Radar mapping at metre-scale spatial resolution, and surface height change detection at centimetre scale, would enable detection of current volcanic & tectonic activity. A lander in the ancient tessera highlands would provide clues as to the earliest geologic record available on Venus. To address these themes we propose a combination of an in situ balloon platform, a radar-equipped orbiter, and (optionally) a descent probe. These mission elements are modelled on the 2010 EVE M3 mission proposal, on the 2010 EnVision M3 proposal, and on Russia's Venera-D entry probe, respectively. Together, these investigations address themes of comparative planetology and solar system evolution. This document was submitted in May 2013 as a response to ESA's Call for White Papers for the Definition of Science Themes for L2/L3 Missions in the ESA Science Programme.

Abstract:

We have searched for the presence of simple P and S-bearing molecules in Titan's atmosphere, by looking for the characteristic signatures of phosphine and hydrogen sulfide in infrared spectra obtained by Cassini CIRS. As a result we have placed the first upper limits on the stratospheric abundances, which are 1ppb (PH3) and 330ppb (H2S), at the 2-σ significance level. © 2013.

Abstract:

The Uranian atmosphere was observed in August 2009 from 0.8 to 1.8. μm using the near-infrared spectrometer, SpeX, at NASA's Infrared Telescope Facility. The observations had a spectral resolution of R=. 1200 and an average seeing of between 0.5' in the H-Band (1.4-1.8. μm) and 0.6' in the I-Band (0.8-0.9. μm). The reduced data were analyzed with a multiple-scattering retrieval code. We were able to reproduce observations when using a vertically-compact cloud in the upper troposphere and a vertically-extended, optically-thin haze above the 1-bar level. The existence of these two clouds is consistent with previous studies.The sub-micron portion of the data are most sensitive to very small scattering particles, allowing more insight into particle size than other portions of the infrared spectrum. This portion of the spectrum was therefore of particular interest and was not available in most previous studies of the planet. We assumed the particles in both clouds to be relatively strong forward scatterers (with a Henyey-Greenstein asymmetry factor of g=. 0.7). Given this assumption, we found single-scattering albedos in the tropospheric cloud particles to be ω̄=0.7 at wavelengths above 1.4. μm and to gradually increase to ω̄=1.0 at wavelengths shortward of 1.0. μm. In the upper haze, we found single-scattering albedos to be ω̄=1.0 with the exception of a narrow drop at 1.0. μm to ω̄=0.6. We found a preference for upper haze particle radii at r=. 0.10. μm. Retrievals of base pressure, fractional scale height, and optical depth in both cloud layers showed the best agreement with data when the base pressure of the upper haze was fixed just above the tropospheric clouds, rather than at or above the tropopausal cold trap. We found that these same retrievals strongly preferred tropospheric cloud particles of 1.35-μm radii, and observed cloud top height to increase away from the equator in the case of latitudinally invariant methane abundance.Latitudinal methane variability was also considered, both through a reflectivity study at the 825-nm collision-induced hydrogen absorption feature, as well as through radiative transfer analysis, using forward modeling and retrievals of cloud properties and methane abundance. The data suggested that methane abundance above the tropospheric clouds increased when moving from the midlatitudes towards the equator by at least 9%. The peak of this equatorial methane enrichment was determined to be at 4. ±. 2° S latitude, having moved nearly 15° northward since a reflectance study of 2002 data (Karkoschka and Tomasko, 2009). © 2013 Elsevier Inc.