Widespread Megaripple Activity Across the North Polar Ergs of Mars

Post contributed by Dr. Matthew Chojnacki, Planetary Science Institute, Lakewood, CO, USA.

Megaripples, which are intermediate-scale aeolian bedforms as compared with ripples and dunes, have been studied extensively on Mars and thought to be largely inactive landforms from past climates. On Earth, “megaripples” can be 30 cm to tens of meters in spacing with an abundant coarse sand population resulting in reduced migration except for very strong storm events. We mapped the extensive sand seas across the north pole of Mars for the presence of Martian megaripples (Image 1). 

Image 1. HiRISE perspective view of north polar dune fields with active megaripples (arrows). Megaripple activity is most evident on the upwind edges of dune fields and in some cases within inter-erg areas. Clusters of contiguous megaripple fields often flanked by ripples and dunes were most common, while occasionally occurrences of mobile megaripple trains atop of bedrock were observed. All images and associated digital terrain models can be accessed at: https://hirise.lpl.arizona.edu/ Credit: NASA/JPL/University of Arizona.

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Titan’s dune fields scanned in the microwave: revealing their true nature

Post by Dr. A Lucas, CNRS Research Scientist, Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005, Paris, France

Titan, Saturn’s largest satellite, has proved to be a world that is both strange and yet so familiar to us. Mountains, lakes, drainage systems and dune fields (Images 1-2) cover its surface. Methane on Titan occupies a similar position to water on Earth. It participates in climatic cycles. Moreover, its photodissociation in the upper atmosphere is responsible for the soot rains that fall on the surface of this icy world. The fate of these grains composed of organic materials is just as essential. Indeed, winds sometimes mobilize them. Over long, very long periods of time, this granular transport is responsible for the formation of vast dune fields located at the equator. But after 13 years of exploration by the Cassini probe, these dunes have not revealed all their secrets. In particular, their morphodynamics are widely debated. Are these bedforms remains from an old time, are they still active today? What is their growth rate? And what is their resulting sediment flux?

Fig1_new

Image 1: Despeckled T8 swath SAR image over the Belet sand dunes located at the Equator of Titan. The dark longitudinal features are the micro-wave absorbent dunes composed of sand made of organics molecules. The bright areas are rough topographic reliefs revealing the icy bedrock beneath the organic sediment cover. Glints (bright spots) are detectable of the crest of some dunes due to specular reflection on their avalanche side.

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