Cosmic Diary by Lori Fenton

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Updated: 4 hours 53 min ago

Layered winds

August 31, 2015

A piece of Mars: On the left is high ground, covered with dunes (or maybe they’re ripples) running from upper left to lower right. On the right is low ground, covered in deeply eroded dunes (ripples?) running almost from left to right. They were probably created at two different times by winds that changed direction in the intervening time. The set on the right is probably much older. (HiRISE ESP_041991_1715, NASA/JPL/Univ. of Arizona)

Stealth bomber dunes

August 26, 2015

A piece of Mars: These dunes look strangely triangular, a little bit like a flock of stealth bombers. Why? They’re two-faced barchans. Each flat face is an avalanche slope that faces downwind, formed by one of two distinct wind patterns that blow in this area (probably seasonally). Dunes like this can form on Earth, but the older slip face tends to be quickly erased as the winds change. (HiRISE ESP_027854_2150, NASA/JPL/Univ. of Arizona)

What is burying what?

July 31, 2015

A piece of Mars: There’s an egg-shaped plateau here (the whole scene is 480×270 m or 525×295 yd across, the “egg” is ~100 m long). It’s partly covered by dunes that have extended across it. Or were the dunes there first and it buried them? Probably the former, but you can try to convince yourself either way. What do you think? (HiRISE ESP_041134_1720, NASA/JPL/Univ. of Arizona)

Dust devils and wind scours on ripples on dunes

July 27, 2015

A piece of Mars: So much wind. There are dark swirly tracks of dust devils that have passed by, ripples covering dunes, wind scours around rocks, and of course dunes. Dune crests have a different color than other regions: are they less covered in dust? made of a more grayish sand that is more easily blown up the dune by the wind? or both? (HiRISE ESP_040885_1295, NASA/JPL/Univ. of Arizona)

Frosty dunes

July 06, 2015

A piece of Mars: In this image (0.96×0.54 km or 0.6×0.33 mi), it’s late winter and the sun is barely above the horizon here near the north pole. The dunes are covered in winter frost, most of which is CO2 ice (also known as dry ice). The dark regions are those facing the sun, where the ice has started to sublimate, revealing the dark sand below. (HiRISE ESP_041433_2650, NASA/JPL/Univ. of Arizona)

Small dunes on Mars

June 01, 2015

A piece of Mars: These dunes are some of the smallest on Mars. The smallest in this frame is ~150 m long (492 ft). But the smallest Earth dunes are ~20 m across. Why are they so much bigger on Mars? The air is thinner, so the wind has to blow stronger to lift sand grains. So once the sand is moving, it goes fast – and therefore goes farther before it lands. This makes for a bigger dune. (HiRISE ESP_41809_1890, NASA/JPL/Univ. of Arizona)

The looming dune

May 25, 2015

A piece of Mars: this 0.96×0.54 km (0.6×0.33 mi) scene shows a large, rippled dune that is slowly marching towards the upper right. The smooth striped band running from upper left to lower right is the slip face, where sand pushed by the wind eventually avalanches. Smaller scars show where slope failures (little landslides) have formed. (HiRISE ESP_027432_1350, NASA/JPL/Univ. of Arizona)