Mechanical disturbances in Fourier spectrometers.

Fourier spectrometers are sensitive to many kinds of disturbance. This focus is mainly on those connected to mechanical vibrations, assessing the relationships between the mechanical inputs and the deriving effects on the spectra. Mechanical vibrations have two main effects on the spectra, the addition of signals due to direct sensitivity to vibrations of the detectors (e.g., through piezoelectric effect) and the changes of the interferogram due to the interferometer optical components motion. The Fourier transform spectrometer considered in this study is based on the constant optical path step sampling achieved by using the interferogram of a reference laser as a trigger so, ideally insensitive to mirrors speed changes, however, the analysis will show how the effects of delays in the sampling chain can compromise the benefits of this configuration. The effects of the vibration of the interferometer optical alignment are considered as well, showing the effect produced on the interferograms and eventually on the spectra. Despite their nonmechanical nature, detector nonlinearity and internal optical reflections are considered as well because their effects, similar to the mechanical ones, could be confused with the latter while in spectra diagnostic it is often important to be able to distinguish between the two. For all the analyzed effects the quantitative relationships between the mechanical disturbances' amplitudes and spectral observed effects are derived.

Global mineralogical and aqueous mars history derived from OMEGA/Mars Express data.

Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the "phyllocian" era) are found in the oldest terrains; sulfates were formed in a second era (the "theiikian" era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the "siderikian") is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

A 5-micron-bright spot on Titan: evidence for surface diversity.

Observations from the Cassini Visual and Infrared Mapping Spectrometer show an anomalously bright spot on Titan located at 80 degrees W and 20 degrees S. This area is bright in reflected light at all observed wavelengths, but is most noticeable at 5 microns. The spot is associated with a surface albedo feature identified in images taken by the Cassini Imaging Science Subsystem. We discuss various hypotheses about the source of the spot, reaching the conclusion that the spot is probably due to variation in surface composition, perhaps associated with recent geophysical phenomena.

Detection of methane in the atmosphere of Mars.

We report a detection of methane in the martian atmosphere by the Planetary Fourier Spectrometer onboard the Mars Express spacecraft. The global average methane mixing ratio is found to be 10 +/- 5 parts per billion by volume (ppbv). However, the mixing ratio varies between 0 and 30 ppbv over the planet. The source of methane could be either biogenic or nonbiogenic, including past or present subsurface microorganisms, hydrothermal activity, or cometary impacts.