What's happening on Mars's surface?

There’s been lots of buzz about the high-altitude cloud on Cloudy Nights and other online discussion forums for skywatchers. Sky & Telescope’s Sean Walker says the puff of white was first noticed on March 20 by Wayne Jaeschke, an amateur astrophotographer from Pennsylvania. Since then, other observers have identified the feature in images going back as far as March 12.

All sorts of hypotheses have been proposed: Could it be debris kicked up by a meteoric impact? Is it a huge weather system? Is it merely a funny kind of glint caused by a combination of lighting and atmospheric conditions?

In an email, Jaeschke told me that the feature is “still there, although it has decreased in size over the past two days.”