Martian sand dunes
fixed in place
DR EMILY BALDWIN
Posted: JULY 9, 2009
Snow and ice trapped inside a number of Martian sand dunes is not enough to prevent their migration, say planetary scientists.
Planetary scientists questioned whether snow and ice trapped inside the dunes might be preventing the movement, but a new study published in the journal Geomorphology, shows that while ice and snow impedes movement of sand dunes in polar climates on Earth compared with dunes in warmer climates, it does not entirely stop the movement, suggesting that other factors are at work.Cemented layers protrude from a dune in North Polar Region of Mars. Image: NASA/Jet Propulsion Laboratory/The University of Arizona.
The study is based on a 30 year survey of Antarctica’s Victoria Valley dune field. Using photos taken between 1961 and 2001 from the USGS Antarctic Resource Center, Mary Bourke of the Planetary Science Institute, and colleagues, estimated the dune migration rates at just 1.5 metres per year, nothing compared to the 30-70 metres that dunes in warm deserts are capable of moving in the same time.
The Antarctic dunes are well known to be covered by seasonal snowfalls and have snow and ice layered inside them. Similarly, Martian sand dunes display similarities to the hard-surfaced sandy deposits found in some of Earth’s deserts, along with compacted icy layers. Dunes on the surface of Mars have been monitored since the first Viking mission in 1975, with recent detailed images attained from the HiRISE (High Resolution Imaging Science Experiment) camera flying on the Mars Reconnaissance Orbiter.
Bourke suggests that the other factors limiting dune movement on Mars could include the planet’s thin atmosphere, which requires very high wind speeds to provide the force needed to move sand, and the water and carbon-dioxide frosts that cover dunes in Mars’ polar regions for 70 percent of the year.
But, Bourke adds, the study of dune movement in Antarctica’s Victoria Valley shows that dunes in the cold weather environments found on Mars, Titan and other frozen bodies still have the potential to move, organize and evolve in the same way that dune fields do on Earth.
In another recent study, Bourke also showed that two small dunes on Mars disappeared completely. The dunes, which were 20 metres wide and located in the north polar region of Mars, were completely eroded away over a period of 5.7 Earth years.
“This (dune disappearance) is fantastic new data, showing that sand is transported on Mars where and when the wind energy is available,” says Bourke. “But the bigger, larger dunes on Mars are not moving, at least in the areas we studied.”
The study covers the longest time period of any cold-climate dune migration and dune dynamics study to date.