There is the possibility, yet, of an extraordinary rain on Mars, by passage of a supernova shock front. For a transitory period, gas and dust from a supernova shock from a distance as far as 10 light years away...such as the one evidenced in sediments by Fe-60 marine deposits on Earth by Fields et al, presumably from Sne blasts in the Local Bubble from OB stars from the Centaurus-Sco Association.
So it would be rare, but not inconceivable. A meteor shower of fine dust, rich in iron oxides,aluminum oxides, pyroxene, olivine followed by atmospheric occluding, and rain. What would look good for this scenario is isotopic analysis of Martian soils to find Sne isotopes by the Mars Science Laboratory.
see:
http://www.journals.uchicago.edu/doi/abs/10.1086/427797
pete