Carbon-dioxide ice cloud on Mars

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).