Planetary atmosphere observation analysis

Abstract:

One of the key problems in determining lunar surface composition for thermal-infrared measurements is the lack of comparable laboratory-measured spectra. As the surface is typically composed of fine-grained particulates, the lunar environment induces a thermal gradient within the near sub-surface, altering the emission spectra: this environment must therefore be simulated in the laboratory, considerably increasing the complexity of the measurement. Previous measurements have created this thermal gradient by either heating the cup in which the sample sits or by illuminating the sample using a solar-like source. This is the first setup able to measure in both configurations, allowing direct comparisons to be made between the two. Also, measurements across a wider spectral range and at a much higher spectral resolution can be acquired using this new setup. These are required to support new measurements made by the Diviner Lunar Radiometer, the first multi-spectral thermal-infrared instrument to orbit the Moon. Results from the two different heating methods are presented, with measurements of a fine-grained quartz sample compared to previous similar measurements, plus measurements of a common lunar highland material, anorthite. The results show that quartz gives the same results for both methods of heating, as predicted by previous studies, though the anorthite spectra are different. The new calibration pipeline required to convert the raw data into emissivity spectra is described also

Abstract:

An emission feature at 220 cm-1 which has been attributed to a cloud of condensed material in Titan's winter stratosphere has been seen for the first time in the south. This feature had previously been found only at high northern latitudes during northern winter and spring. The material emitting at 220 cm-1, as yet unidentified, may be volatiles associated with nitrile gases that accumulate in the absence of ultraviolet sunlight. Not detected as recently as 2012 February, the 220 cm-1 feature clearly appeared at the south pole in Cassini spectra recorded on 2012 July 24, indicating a rapid onset of the emission. This is the first indication of the winter buildup of condensation in the southern stratosphere that has been expected as the south pole moves deeper into shadow. In the north the 220 cm-1 feature continued to decrease in intensity with a half-life of 3 years. © 2012. The American Astronomical Society. All rights reserved.

Abstract:

Ammonia (NH3) has been detected both on Saturn and Jupiter, and although its concentration and distribution has been well-studied on Jupiter, it has proven more difficult to do so on Saturn due to higher sensitivity requirements resulting from Saturn's lower atmospheric temperatures and the dominance of Saturn's phosphine which masks the ammonia signal. Using far-infrared measurements of Saturn taken by Cassini/CIRS between February 2005 and December 2010, the latitudinal variations of upper tropospheric ammonia on Saturn are studied. Sensitivity to NH3 in the far-infrared is explored to provide estimates of temperature, para-H2 and PH 3, from 2.5 cm-1 spectral resolution measurements alone, 0.5 cm-1 spectral-resolution measurements alone, and 0.5 cm -1 measurements degraded to 2.5 cm-1 spectral resolution. The estimates of NH3 from these three different datasets largely agree, although there are notable differences using the high emission angle 0.5 cm-1 data, which are asserted to result from a reduction in sensitivity at higher emission angles. For low emission angles, the 0.5 cm -1-retrieved values of NH3 can be used to reproduce the 2.5 cm-1 spectra with similar efficacy as those derived directly from the 2.5 cm-1 resolution data itself, and vice versa. Using low emission angle data, NH3 is observed to have broad peak abundances at ±25°latitude, attributed to result from condensation and/or photolytic processes. Lack of data coverage at equatorial latitudes precludes analysis of NH3 abundance at less than about 10°latitude. Noise levels are not sufficient to distinguish fine zonal features, although it seems that NH3 cannot trace the zonal belt/zone structure in the upper troposphere of Saturn. © 2012 Elsevier Ltd. All rights reserved.