Vertical profiles of dust and ozone in the martian atmosphere deduced from solar occultation measurements

THE most sensitive parameter in a chemical model of the martian atmosphere is the vertical profile of ozone concentration, which has not previously been measured. Solar occultation measurements performed on the Phobos 2 spacecraft in martian orbit have provided us with such profiles, together with evidence for the existence of particles of small dimensions (0.1-μm diameter) in the 50- to 20-kilometre altitude range. These particles could be H2O ice at the top of the observed range and dust at lower altitudes, possibly haematite, with a wide range of dimensions (down to nanocrystal size), dispersed in some other material (H2O ice or silicates, for example). The relatively large number of these solid particles opens up the possibility of heterogeneous chemistry having a major role in the atmosphere of Mars.

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