15 December 2009
Twisters on Mars
Posted by Michael McFadden
The Wizard of Oz was my favorite movie as a child, but the tornado scene gave me fascinating nightmares for decades. That’s why I grabbed onto a new study about Martian dust devils.
It turns out there are way more dust devils on Mars than scientists thought. These swirling clouds are visible on video from the Mars Spirit rover in higher concentrations than previously predicted by satellite images of their tracks from the Mars Reconnaissance Orbiter, which takes hi-res pictures from space. Most of the twisters on video were smaller than the tracks seen from space, meaning there are lots of small funnels that don’t leave a trace in Martian dirt–to leave a trace, the twisters have to have enough strength to suck up the top dust later and expose the darker dirt below (as in the MRO image above), which is why smaller devils aren’t recorded in tracks.
Now, by matching up the number of tracks seen from space with the actual number of twisters seen on the surface, scientists can predict how often twisters occur based on the couple of tracks left behind. Such studies show that are more twisters in Martian summer than winter. These results were presented at an early afternoon poster session (P23A) on Tuesday by researchers from the US Geological Survey in Flagstaff, Arizona.
“It’s a first comparison between orbital observations of dust devil tracks and surface observations of dust devils,” said Paul Geissler, who co-authored the study with his student Circe Verba.
This is important because more dust devils mean more dirt in Mars’ atmosphere, which is a key factor in Martian climate models. The dust absorbs heat from the Sun and heats the atmosphere, which drives global circulation intensity.
“I do climate mod on Mars and this is a big source of dust in the atmosphere on Mars,” said Jeffrey Hollingsworth of the NASA Ames Research Center in Mountainview, Calif. “We parameterize this on global climate models using very primitive methods. Who knows if we’re getting it right if we’re not getting the dust cycle right?”
–Gwyneth Dickey UC Santa Cruz Science Communication Graduate Student
The point of the study with the MRO HiRISE comparison and MER Spirit is that only larger dust devils leave behind tracks visible to see from Orbit. Average orbital track diameters were 40-60 m in comparison to Spirit’s 10-20 m wide plumes and that the season extended longer than first seen by Spirit.