Mysterious high-rise clouds seen appearing suddenly in the martian atmosphere on a handful of occasions may be linked to space weather, say Mars Express scientists. [The results are published in the Journal of Geophysical Research.]
Amateur astronomers using telescopes on Earth were the first to report an unusual cloud-like plume in 2012 that topped-out high above the surface of Mars at an altitude around 250 km. The feature developed in less than 10 hours, covered an area of up to 1000 x 500 km, and remained visible for around 10 days.
The extreme altitude poses something of a problem in explaining the features: it is far higher than where typical clouds of frozen carbon dioxide and water are thought to be able to form in the atmosphere.
Indeed, the high altitude corresponds to the ionosphere, where the atmosphere directly interacts with the incoming solar wind of electrically charged atomic particles. [More at link]