Last year, images from the High Resolution Imaging Science Experiment (HiRISE) on NASA's Mars Reconnaissance Orbiter captured sand dunes and ripples moving across the surface of Mars — observations that challenged previously held beliefs that there was not a lot of movement on the planet's surface. Technology developed by a team at the California Institute of Technology (Caltech) has now allowed scientists to measure these activities for the first time. Using COSI-corr (Co-registration of Optically Sensed Images and Correlation) software, which was invented at Caltech, a team of researchers looked at a specific field of sand dunes called Nili Patera.

The team focused on precise, subpixel measurements of movement between pairs of images. On the dunes at Nili Patera, the software automatically measured changes in the position of sand ripples from one image to another over a 105-day period, resulting in the surprising findings that the ripples are moving fast — some upwards of 4.5 meters during that time —which contributes to the total motion of the sand dunes. "This is the first time that we have full, quantitative measurement of an entire dune field on a planetary surface, as opposed to the localized manual measurements that were done before," says Caltech scientist Francois Ayoub. "This is a huge step in terms of the data that you can obtain from the surface of Mars."

The team also found that the dunes at Nili Patera appear to move similarly to those found on Earth in Victoria Valley, Antarctica. This implies that the rates of landscape modification due to wind are similar on the two planets. Interestingly enough, getting these measurements was much easier on Mars — the researchers could not quantify dune ripple migration rates on Earth using the same technique because that would require satellite imagery of our planet at a resolution that makes it classified information.

"These new measurements provide keys to interpreting the landscape and the stratigraphic record that you see exhumed when you look at the imagery—we see sediments and wonder what they mean in terms of the past geologic history," says Jean-Philippe Avouac, the professor of geology at Caltech who initiated the study. "The fact that you can describe the current activity of surface systems will help us understand Mars's past geological record, which is a reason that this is important."

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