Even though NASA’s Curiosity rover mostly focuses on Mars’s bedrock, every few days it observes the sky. Last summer, the rover has shot the first ground-based view of Martian clouds shaped by gravity waves as recently reported at the Lunar and Planetary Science Conference. These shots are the best record made so far of a mysterious recurring belt of equatorial clouds known to influence the martial climate.
“Understanding these clouds will help inform estimates of ground ice depth and perhaps recurring slope lineae, potential flows of salty water on the surface,” says John Moores, a planetary scientist at York University in Toronto, Canada, who led the study with his graduate student, Jake Kloos. “If we wish to understand the water story of Mars’s past,” Moores says, “we first need to [separate out] contributions from the present-day water cycle.”
During Curiosity’s 1302th martian day, it saw a sequence of straight, parallel rows of clouds flowing in the same direction, known as gravity wave clouds. Not to be confused with gravitational waves, gravity waves are atmospheric ripples that result from air trying to regain its vertical balance. Similar to the waves that follow a pebble tossed into a pond, gravity waves are created when some unknown feature of the martian landscape causes a ripple in the atmosphere that is then seen in clouds. Such waves are common at the edge of the martian ice caps, but thought to be less frequent over its equator.
It is not certain those are gravity waves, however. They could also be “cloud sheets”, a similar looking pattern that’s potentially associated with strong winds striking heated air parcels as they near the top of the lower atmosphere.
Adopted from the article by Paul Voosen in “Science Magazine”