HiRISE images

The Mars Global Digital Dune Database
Published 5/30/2018 in Lori Fenton's Blog Author lfenton
There are a lot of dune fields on Mars. Over the last ten years I've been part of a group that's mapped out the big dark dunes on the planet to see where they form, and to understand the sedimentary and meteorological processes that control their formation. We compiled a database showing their locations and various physical characteristics. Wait, why do piles of sand form in the first place? On Earth, it's because: 1. There's a lot of sand (not a surprise). 2. There's a lot of strong wind (also not a surprise). 3. The sand is free to be moved by the wind.... read more ❯

Published 5/9/2018 in Lori Fenton's Blog Author lfenton
Here's a grand dune, making its stately way northward under winds blowing mainly from the south-southeast (bottom to top), with a secondary wind blowing from the southwest (lower left to upper right). There are two rippled and sharp-crested slip faces on this dune -- can you identify both of them (hint: each wind creates one slip face on the downwind side)?   The dune is ~750 m (2,460 ft) long. It's made of dark sand the wind blows along the ground until it piles up into these big... read more ❯

Wild & dark lacy dunes on twisty bright layers
Published 4/30/2018 in Lori Fenton's Blog Author lfenton
Some windblown dunes on Mars are just beyond words. Take these beasts in this 0.95x0.95 km (0.59x0.59 mi) scene: These are a peculiar type of bedform called a transverse aeolian ridge, or TAR for short, with a spacing of about 50 m (164 ft). Nobody really understands these things: are they dunes or ripples or something totally different? They're common on Mars but unusual (maybe even nonexistent) on Earth. They're also pretty dark-toned here, whereas on most of Mars they tend to be lighter than the surrounding rocks. The TARs mostly cover the surface,... read more ❯

Squish! ????
Published 4/20/2018 in Lori Fenton's Blog Author lfenton
This isn't a full blog post. Just something I saw while looking around for other things on Mars. And for once it's (probably) not related to the wind. But it's cool enough to share. I saw something that went "squish" ???? . This is a ~1.2 km (0.75 mi) wide crater in the northern mid-latitudes of Mars. I don't know much about this region geologically (haven't done my homework, as this is just a quick look). This crater has a set of layers in it that have partially eroded away. And underneath those layers on the crater floor are what look like... read more ❯

Flow. Lots of flow.
Published 4/16/2018 in Lori Fenton's Blog Author lfenton
Over the years, many things have flowed across the surface of Mars: lava, ice, water, and wind. Two things have flowed in this image (the view is 0.75x0.6 km or 0.47x0.37 mi): Image credit: HiRISE ESP_026541_1840, NASA/JPL/Univ. of Arizona If you know my blog at all, then you might recognize the big structures as yardangs. They are part of an enormous set of yardangs on Mars called the Medusa Fossae Formation. At some point in the past, probably a few billion years ago, the wind kicked up a bunch of sand that carved out these structures, blowing from the lower left to... read more ❯

Wind-exposed layers
Published 3/26/2018 in Lori Fenton's Blog Author lfenton
On Earth, layers comprising the geological record of an area are most often exposed by fluvial erosion, as a river cuts through rock (a typical example is the Grand Canyon). On Mars, fluvial channels are not so common (especially in the past few billion years). But the wind has relentlessly worked away at the surface, sometimes revealing strata laid down long ago. Click on the image for more detail. This is a tiny bit (0.5x0.375 km, or 0.31x0.23 mi) of the side of an "Interior Layered Deposit" in the middle of Candor Chasma, called Juventae Mensa. Wind blowing from the upper... read more ❯

Dune trails deep in Hebes Chasma, Mars
Published 3/19/2018 in Lori Fenton's Blog Author lfenton
A few weeks ago I wrote about dunes leaving behind trails near the north pole of Mars. They do this in a few other places as well, but it's not very common. Below is a rare example, this time on the floor of Hebes Chasma (one of the Valles Marineris), which is a tectonically-opened hole in the ground that's about 6 km deep. I don't mean to repeat the same topic, but geologists are usually drawn to terrain that so plainly lays out the geological story of an area, and obvious dune-generated layers are pretty rare. (Also pretty.) (HiRISE ESP_045586_1585, NASA/JPL/Univ.... read more ❯

Wind on Mars and the Huygens-Fresnel Principle
Published 3/12/2018 in Lori Fenton's Blog Author lfenton
How about some basic physics? It'll be easy, I promise. Just look at the pretty picture below (click on it to see it better): (HiRISE ESP_045586_1585, NASA/JPL/Univ. of Arizona) The big crater is ~400 m (1/4 mile) across. Wind blows sediment from the top to the bottom of the view, making some dune-like features (TARs, really) at the top and inside the crater. The rim at the top of the crater has a set of hills with a dip inbetween them, which allows wind and sediment to be funneled into the crater through a narrow valley. Once inside the crater, the wind... read more ❯

"Baby" dunes on Mars are big
Published 3/5/2018 in Lori Fenton's Blog Author lfenton
Baby dunes on Mars are pretty big compared to those on Earth. In this 885x512 m (0.55x0.32 mi) frame, there are four dunes of roughly the same size, all of which are about as small as dunes can get on Mars. They're ~180 m (590 ft) across, several times bigger than similar "elementary" dunes on Earth. There's another key difference between Earth and Mars dunes. The avalanching lee slope (the slip face) comes to a point in these dunes. That's because there are two winds forming these dunes, one from the upper right and one from the upper left. On Earth,... read more ❯

Dune trails
Published 3/1/2018 in Lori Fenton's Blog Author lfenton
There's so much going on in this 0.75x0.75 km (0.47x0.47 mi) image. You're looking at a broad dune migrating toward the upper right. It's early summer, but this is close enough to the north pole that some winter ice lingers (pale blueish white), amid slumps that have shed down from the dune. The slumps probably form as ice weighs down the dune sand -- they are not seen on dunes at lower latitudes, where ice is less common. The upwind side of the dune is interesting as well. The dark dune slowly migrates forward, leaving behind bits of itself (sort of... read more ❯

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