Mars Has Un-Earthly Wind Ripple Dunes
It’s been known for decades that sand dunes cover many areas of Mars, but new findings show that these dunes are covered with two sizes of wind ripples – a phenomena that doesn’t exist on Earth and occurs on Mars because of its low-density atmosphere, according to a study that includes a Texas A&M University researcher.
Ryan Ewing, assistant professor in the Department of Geology and Geophysics at Texas A&M, along with A&M undergraduate student Matt Ballard, and colleagues from the California Institute of Technology, John Hopkins University, University of California-Santa Cruz, the University of Texas, Western Washington University, University of California-Davis, the Planetary Science Institute in Tucson, Ariz., Imperial College of London and NASA have had their work published in the current issue of Science magazine.
Using images and data collected by NASA’s Mars rover Curiosity, the team found that winds on Mars produce two distinct sizes of wind ripples – ripples are similar in shape to sand dunes, but much smaller in size. The smallest ripples are spaced about 4 inches apart and appear to be like wind ripples that form on Earth. The larger ripples are about 1 foot high, spaced about 10 feet apart and are unlike any ripple found on Earth. It appears these large ripples are quite common on the Red Planet.
“We knew the large ripples were all over Mars,” says Ewing.
“We and other researchers had detected them in many locations using satellite data, but this is the first time we’ve seen them up close. We weren’t sure we’d see the small ripples on top of the big ripples and when we did we knew we had something different than exists on Earth.” They think the reason the big ripples exist on Mars and not Earth is because Mars’ atmosphere is less dense – about 60 times less dense.
“That means the sand grains react to the wind differently than they would here on Earth.”
Although the smaller ripples have a familiar-Earth like shape, the larger ripples don’t look like typical ripples formed by wind, Ewing explains. Rather than being very straight and having a low profile, these ripples are sinuous and winding and have steep slopes, which, the team recognized, is much more like ripples formed in water. Although they appear to have been shaped by water, the team knows that is definitely not how they were formed.
“The ripples look like they were formed by water, but we know these ripples are active in today’s winds on Mars,” Ewing notes. “But we think some of the same physics that applies to water ripples also applies to these Martian ripples.”
The team concluded that the ripples form by drag in the wind, similar to how ripples in water form. Ewing says that this can happen because the low density of Mars atmosphere. They determined that because the ripple size depends on the density of the atmosphere, if they existed in Mars’ ancient history, they could be telling of Mars’ past atmosphere and climate.
Ewing says that analyses of sandstone rocks from another location on Mars shows evidence that the ripples existed on Mars about 3.7 billion years ago.
“Finding evidence of these ripples in the rocks tells us that Mars has had a thin atmosphere for a long time,” he adds.
“It has been interesting learning about processes on Mars that are happening today and that can tell us something about Mars’ ancient past. It is how a lot of geology is done on Earth and now we are applying this to Mars.”
He adds that “we are learning more about climatic and sedimentary processes, which are two key topics currently driving Martian science.”