Megaripple activity widespread on Martian north pole

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2 cap retreat. The view is approximately one kilometer in width. Credit: HiRISE digital terrain model DTEPC_036176_2640_035926_2640_A01 and color orthoimage ESP_053345_2640. HiRISE data: NASA/JPL/University of Arizona” width=”600″>
Megaripples are wind-driven bedforms found on Mars and Earth’s surface. In this perspective view using data from the High Resolution Imaging Science Experiment, (HiRISE), megaripples can be seen at the bottom of the center next to the north-polar sand dunes. These northern polar megaripples and dunes yield the highest known sand fluxes on the planet, driven by summer katabatic winds modulated by the seasonal CO2 cap retreat. The view is approximately one kilometer in width. Credit: HiRISE digital terrain model DTEPC_036176_2640_035926_2640_A01 and color orthoimage ESP_053345_2640. HiRISE data: NASA/JPL/University of Arizona

Megaripples, intermediate-scale bedforms caused by the action of the wind, have been studied extensively and thought to be largely inactive relics of past climates, save for a few exceptions. Matthew Chojnacki, Planetary Science Institute Research Scientist, has published a new paper showing that megaripples were abundant in the north polar region on Mars. They were discovered to be migrating along with ripples and dunes.

Megaripples on Mars are about 1 to 2 meters tall and have 5 to 40 meter spacing, where their 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. Megaripples migrate at an average rate of 0. 13 meters per Earth year), some of the nearby ripples were found to migrate an average equivalent of 9.6 meters per year over just 22 days in northern summer–unprecedented rates for Mars. This megaripple activity is explained by the high rates of sand movement.

“Using repeat HiRISE images acquired over long durations–six Mars years or 13 Earth years–we examined the dynamic activity of polar bedforms. The Martian atmosphere’s thinness can mobilise some megaripples of coarse-grained grain, reversing previous notions that these were static landforms from the past. We mapped megaripples and adjacent bedforms across the north polar sand seas, the most expansive collection of dune fields on Mars,” said Chojnacki, lead author of “Widespread Megaripple Activity Across the North Polar Ergs of Mars” that appears in Journal of Geophysical Research: Planets.

Sites of polar bedforms with active megaripples as seen in HiRISE Approximate transport direction is toward the lower left and the inset is 100 meters wide. Credit: HiRISE data from NASA/JPL/University of Arizona

Part of the uncertainty in studying planetary-polar landforms is that the region eventually gets covered by carbon dioxide and water. Megaripples and other wind-driven bedforms are not able to migrate for almost half of the year. Chojnacki stated that it seems the late spring and summer winds from the polar caps more than compensate for the inactivity.

“Megaripples were found to be widespread across the region and migrating at relatively high rates relative to other sites on Mars that are at lower latitudes. The increased activity may be due to the higher sand fluxes for nearby dunes, which are driven by summer-time seasons when polar ice melts. This suggests that the Martian surface is constantly being altered and not static. Chojnacki stated. “In contrast, megaripples in other areas seem to have stabilized. This is likely due to inter-granular Ice within low wind zones.”

More information:
Matthew Chojnacki et al, Widespread Megaripple Activity Across the North Polar Ergs of Mars, Journal of Geophysical Research: Planets (2021). DOI: 10. 1029/2021JE006970

Citation:
Widespread megaripple activity found on Martian north pole area (2022, January 12)
retrieved 13 January 2022
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