Scientists discover that mid-sized dunes near Mars’ north pole move

Mars' North Pole

Scientists using images from Mars Reconnaissance Orbiter (MRO) collected over six Martian years (6.5 Earth years) have found that the mid-sized dunes dubbed mega-dunes near the north pole actually do move from year to year, unlike similar sized dunes elsewhere on the planet.

Megaripples on Mars are about 1 to 2 meters tall and have 5 to 40 meter spacing, where there size falls between ripples that are about 40 centimeters tall with 1 to 5 meter spacing and dunes that can reach hundreds of meters in height with spacing of 100 to 300 meters. Whereas the megaripples migration rates are slow in comparison (average of 0.13 meters per Earth year), some of the nearby ripples were found to migrate an average equivalent of 9.6 meters (32 feet) per year over just 22 days in northern summer – unprecedented rates for Mars. These high rates of sand movement help explain the megaripple activity.

Previously it was believed that such dunes were static planetwide, left over from a time when Mars’ atmosphere was thicker and could then move them more easily. This data however suggests that the winds produced over the north pole when the carbon dioxide in the atmosphere freezes in winter and sublimates back to a gas in summer are sufficient to shift these dunes in the surrounding giant Olympia Undae dune sea.

The wavy and beautiful edge of the northern ice cap of Mars

The scarp of the north pole icecap on Mars
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on August 7, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the many layered scarp that forms the edge of the northern polar ice cap on Mars, probably more than 2,000 feet high.

Those layers are significant, as they indicate the many climate cycles that scientists think Mars has undergone over the eons as the red planet’s rotational tilt, or obliquity, rocked back and forth from 11 degrees inclination to as much as 60 degrees. At the extremes, the ice cap was either growing or shrinking, while today (at 25 degrees inclination) it appears to be in a steady state.

Why the layers alternate light and dark is not known. The shift from lighter colors at the top half and the dark bottom half marks the separation between the top water ice cap and what scientists label the basal unit. It also marks some major change in Mars’ climate and geology that occurred about 4.5 million years ago.
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A weak avalanche season on Mars?

The north pole scarp
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Today’s cool image from Mars is cool both for what is visible in the photo and for what is not, the latter of which might turn out to be a discovery of importance.

The photo to the right, cropped and reduced to post here, was taken on June 24, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a section of the edge of Mars’ north polar ice cap, with north at the top.

This scarp is probably more than 2,000 feet high, though that height drops to the south as the upper layers disappear one by one from either long term erosion or sublimation. Those layers represent the visible information in the photo that is cool. They give us tantalizing clues about the geological and climatic history of Mars. Each layer probably represents a climate period when the north icecap was growing because the tilt of the planet’s rotation was even less than the 25 degrees it is now. When that tilt is small, as small as 11 degrees, the poles of Mars are very cold, and water ice migrates from the mid-latitudes to the poles, adding thickness to the icecaps. When the tilt grows, to as much as 55 degrees, the mid-latitudes are colder than the poles, and the water ice migrates back to the mid-latitudes.

What is not visible in this picture, however, might be far more significant.
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