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.