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Ice clouds put Mars in the shade   This image composite shows the carbon-dioxide-ice (CO2) cloud detected by OMEGA imaging spectrometer aboard ESA’s Mars Express on 12 June 2004, during spring in the northern hemisphere. At that time, Mars Express was flying at more than 2000 km over the surface of the planet. The cloud was situated at 80 km altitude. The four images of the cloud were taken at four distinct wavelengths. The 4.26 micron image (third from the left) allowed a clear and unambiguous spectral detection of the cloud. Interestingly, while the cloud itself only appeared at in the 0.5- 4.26-micron images, its shadow, which is located 100 km southwest, remained visible at all wavelengths covered by OMEGA.
The opacity of this cloud is estimated to be greater than 0.5, corresponding to a 40 % dimming of the sunlight. The size of the cloud particles size is 1.5 microns (1.5/1000 of a millimetre).  These images show another high-altitude carbon-dioxide-ice (CO2) cloud detected in the equatorial region of Mars by the OMEGA instrument aboard ESA’s Mars Express about two weeks after the detection of another CO2-ice cloud on 12 June 2004. The shadow of the cloud can be spotted on the surface, elongating across the rim of an impact crater.  This image composite provides one of the most striking examples of a carbon-dioxide-ice (CO2) cloud occurring in the mesosphere of Mars, imaged at different wavelengths. This was one of the first detections of a CO2-ice cloud by the OMEGA instrument on board ESA’s Mars Express, and one of the first images ever to be identified as of CO2-ice cloud. Here, the cloud stretches over the Terra Meridiani region, and covers an area more than 200 km wide.
The image also includes the spectrum obtained by OMEGA and showing that CO2-ice is the actual composition of the cloud. Release date: 12 March 2008 |