Curiosity rover finds surprising sand dunes
Studies of the “Bagnold Dunes” by NASA’s Curiosity Mars rover have resulted in the discovery of unusual types of wind-sculpted sand ripples not found on Earth. The rover began its investigation of the dunes on the northwestern flanks of Mount Sharp six months ago.
“Earth and Mars both have big sand dunes and small sand ripples, but on Mars, there’s something in between that we don’t have on Earth,” said Mathieu Lapotre, a graduate student at Caltech in Pasadena, California, and science team collaborator for the Curiosity mission. He is the lead author of a report about these mid-size ripples published in the July 1 issue of the journal Science.
Both Earth and Mars have true dunes which are usually larger than a football field, with downwind faces shaped by sand avalanches, which make them much steeper than the upwind faces.
Earth also has small ripples that typically appear in rows less than a foot (<30 centimeters) apart, that are formed by wind-carried sand grains colliding with other sand grains along the ground. These “impact ripples” sometimes corrugate the surfaces of sand dunes and beaches.
Images taken of Martian sand dunes have shown ripples about 10 feet (3 meters) apart on dunes’ surfaces. Until Curiosity began studying Bagnold Dunes, the interpretation was that impact ripples on Mars could be several times the size of impact ripples on Earth. Features the size of Earth’s impact ripples could not be seen at the resolution of the images taken from orbit and would not be expected to be present if the meter-scale ripples were impact ripples.
“As Curiosity was approaching the Bagnold Dunes, we started seeing that the crest lines of the meter-scale ripples are sinuous,” Lapotre said. “That is not like impact ripples, but it is just like sand ripples that form under moving water on Earth. And we saw that superimposed on the surfaces of these larger ripples were ripples the same size and shape as impact ripples on Earth.”
Another similarity between the mid-sized ripples on Mars and underwater ripples on Earth is that, in both cases, one face of each ripple is steeper than the face on the other side and has sand flows, as in a dune. Scientists have concluded that the meter-scale ripples are built by Martian winds dragging grains of sand in the same manner that water drags sand on Earth.
“The size of these ripples is related to the density of the fluid moving the grains, and that fluid is the Martian atmosphere,” Lepotre said. “We think Mars had a thicker atmosphere in the past that might have formed smaller wind-drag ripples or even have prevented their formation altogether. Thus, the size of preserved wind-drag ripples, where found in Martian sandstones, may have recorded the thinning of the atmosphere.”
The scientists checked ripple textures preserved in sandstone for over 3 million years at sites studied by NASA’s Curiosity and Opportunity rovers. The team found wind-drag ripple approximately the same size as modern ones on active dunes. This observation fits with other data that suggests that Mars lost most of its original atmosphere early in the planet’s history.
Other discoveries from Curiosity’s investigations at Bagnold Dunes shoe similarities between how dunes behave on Mars and Earth.
“During our visit to the active Bagnold Dunes, you might almost forget you’re on Mars, given how similar the sand behaves in spite of the different gravity and atmosphere. But these mid-sized ripples are a reminder that those differences can surprise us,” said Curiosity Project Scientist Ashwin Vasavada, of NASA’s Jet Propulsion Laboratory in Pasadena.
Video courtesy of NASA/JPL
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.