ESA Science & Technology30-Jun-2005 09:08:03
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Mars Express Analyses the Earth

OMEGA Spectral Analysis

July 3, 2003, OMEGA acquired spectra of the Earth and its Moon.

From the 8 millions of km distance, the Earth filled about one OMEGA pixel. Thus, the spectrum corresponds to the entire illuminated crescent, dominated by the Pacific Ocean. The spectrum covers the visible and near-infrared spectral domain, from 0.35 to 5.15 Ám, with a spectral sampling varying from 4 to 20 nm.

First OMEGA spectrum of the Earth

Both major and minor atmospheric species could be readily identified, through their absorption features in the scattered solar spectrum (below 3 Ám) and the thermal planetary emission (above 3 Ám), with a very high signal/noise ratio. H2O and CO2 dominate, with all predicted bands present. The molecular oxygen O2 is also easily identified in the visible and near-infrared region. Ozone could also be identified, as well as methane, by their IR signatures. Many other features are present, that will be processed in the coming days. Along the observation, the Earth rotated so as to offer a varying observed surface. Correlated variations in the atmospheric content will be searched for, that could account for non fully mixed species (CH4 in particular).

These Earth observations by OMEGA, in the 0.35-5.15 micron range, have several unique features, of interest for a variety of scientists. The NASA/Galileo mission observed the Earth during two encounters in 1990 and 1992, and some interesting observations were reported from the NIMS IR investigation, but without the possibility of observing the global spectrum, due to saturation effects on the instrument, not designed for observing too bright objects. For OMEGA, small integration times have been purposely chosen. In addition, the global disk of the Earth was observed at high phase angle, contrary to usual low orbit observation. Such global disk spectra are useful to prepare future observations of Earth-like planets, as for the Darwin mission.

Major species features in the 1-2.5 Ám range

Major species features in the 2.5-5.1 Ám range



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