Simon Calcutt

Abstract:

Observations of Neptune were made in September 2009 with the Gemini-North Telescope in Hawaii, using the NIFS instrument in the H-band covering the wavelength range 1.477-1.803 μm. Observations were acquired in adaptive optics mode and have a spatial resolution of approximately 0.15-0.25″. The observations were analysed with a multiple-scattering retrieval algorithm to determine the opacity of clouds at different levels in Neptune's atmosphere. We find that the observed spectra at all locations are very well fit with a model that has two thin cloud layers, one at a pressure level of ∼2. bar all over the planet and an upper cloud whose pressure level varies from 0.02 to 0.08. bar in the bright mid-latitude region at 20-40°S to as deep as 0.2. bar near the equator. The opacity of the upper cloud is found to vary greatly with position, but the opacity of the lower cloud deck appears remarkably uniform, except for localised bright spots near 60°S and a possible slight clearing near the equator. A limb-darkening analysis of the observations suggests that the single-scattering albedo of the upper cloud particles varies from ∼0.4 in regions of low overall albedo to close to 1.0 in bright regions, while the lower cloud is consistent with particles that have a single-scattering albedo of ∼0.75 at this wavelength, similar to the value determined for the main cloud deck in Uranus' atmosphere. The Henyey-Greenstein scattering particle asymmetry of particles in the upper cloud deck are found to be in the range g∼ 0.6-0.7 (i.e. reasonably strongly forward scattering).Numerous bright clouds are seen near Neptune's south pole at a range of pressure levels and at latitudes between 60 and 70°S. Discrete clouds were seen at the pressure level of the main cloud deck (∼2. bar) at 60°S on three of the six nights observed. Assuming they are the same feature we estimate the rotation rate at this latitude and pressure to be 13.2 ± 0.1. h. However, the observations are not entirely consistent with a single non-evolving cloud feature, which suggests that the cloud opacity or albedo may vary very rapidly at this level at a rate not seen in any other giant-planet atmosphere. © 2011 Elsevier Inc.

Abstract:

Accurate measurement of the temperature, composition and dynamics of Jupiter's atmosphere is one of the main scientific goals of ESA's and NASA's Outer Planet Mission proposals. Infrared remote sounding provides a powerful tool for achieving these objectives and was used by Voyager/IRIS and Cassini/CIRS, but is insensitive to some altitudes and gases. The sub-millimetre wavelength (terahertz) region of the electromagnetic spectrum, which has not been significantly exploited to date in the discipline of planetary science, provides unique spectral information over a range of atmospheric pressures and, when combined with infrared data, is a powerful in situ planetary atmospheric sounder. We will describe a novel low mass and low power consumption combined terahertz/IR instrument proposed for inclusion on the Jupiter Ganymede Orbiter that will greatly improve our understanding of the atmosphere of Jupiter. Through the combination of high spectral resolution 2.2THz spectroscopy (R=10⁶) and lowspectral resolution IR radiometry, the entire temperature profile of the Jovian atmosphere from 0.6 to 10^-3 bar can be evaluated (filling in the currently unmeasured levels between 0.1 and 0.01 bar). In addition, the tropospheric and stratospheric composition can be determined (especially water vapour) and observations of the Doppler shifting of sub-millimetre lines can also be used to measure horizontal wind speeds.

Abstract:

Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.