Cosmic Diary by Lori Fenton

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Lumpy bumpy dunes

September 30, 2014

A piece of Mars: These funny shaped dunes were formed by winds blowing from two directions – one from the top of the frame and one from the upper right. Both winds make steep slopes (slip faces) on the downwind (lee) sides of the dunes. With enough sand supply, the “point” between the slip faces will continue to extend toward the lower left as the two winds take turns driving the sand back and forth. (HiRISE ESP_037203_2555, NASA/JPL/Univ. of Arizona)

Changing winds

September 22, 2014

A piece of Mars: There are two sets of ripples here: tan ones and gray ones, each oriented to a different wind (scene is 300×225 m, or 984×738 ft). The gray ones sit on top of the tan ones, so the gray ones are younger. Now come the fun questions: why the different colors? Are they made out of different material (and if so, why), or are the older tan ones different because the gray sediment has weathered to tan over time? (HiRISE PSP_002387_1985, NASA/JPL/Univ. of Arizona)

Missing bedrock

September 15, 2014

A piece of Mars: Wind flow on Mars can be quite dramatic. Here, a single wind-sculpted hill stands 1.5 km (0.93 mi) wide and 600 m (1970 ft) high (color shows elevation). That sounds big, but vastly larger is the volume of material that has been removed to form it. A sandy ridge forming a “bow shock” indicates present-day winds still blow in the same direction. (HiRISE ESP_017173_1715, NASA/JPL/Univ. of Arizona)

Martian waves

September 08, 2014

A piece of Mars: The swirly candy stripes in these big dark dunes are layers inside that have been made visible by wind erosion (the scene is 1.5×0.9 km, or 0.93×0.56 mi). It’s rare to see the inside structure of dunes like this, but these are being eroded by wind blowing from the upper right. For similar examples on Earth, check out The Wave. (HiRISE ESP_037200_1765, NASA/JPL/Univ. of Arizona)

Holes around rocks

September 03, 2014

A piece of Mars: This scene (509×382 m, or 1670×1253 ft), aside from showing some lovely rippled dunes, has many car-sized boulders in it. Some are surrounded by ditches in the sand, like little moats. Why? The sand is blown away from the ground as wind impacts the rocks. My colleague Mark Bishop has studied these in more detail (read more here) (HiRISE ESP_037201_2450, NASA/JPL/Univ. of Arizona)

Which wind came first?

August 25, 2014

A piece of Mars: This scene (3.9×2.5 km or 2.4×1.6 mi) shows a surface carved by two different winds: one blowing from the right and one blowing from the bottom right. They’ve formed overlapping sets of streamlined rocks called yardangs. Can you tell which set of yardangs was formed first? It’s a little more complicated than it may first appear. (HiRISE ESP_037156_1800 NASA/JPL/Univ. of Arizona)

How the wind turns

August 18, 2014

A piece of Mars: The two shadowed hills in the upper part of this frame (497×373 m or 1631×1224 ft across) rest on a flat plain covered in large ripples. On the plain the ripples are aligned north-south, formed perpendicular to a wind blowing from the east (right). But those hills block the wind and turn it, so that the ripples between the hills change direction. This is how windblown landforms can be used as wind vanes in remote places (like on Mars). (HiRISE ESP_037188_1835, NASA/JPL/Univ. of Arizona)

Wind within vs. wind without

August 14, 2014

A piece of Mars: Dunes outside the crater are straight but the ones inside the crater look like a spiderweb. Why? This image shows just how much the topography of a crater wall can affect the wind, which produces a much more complex set of dunes inside than out on the plains. (HiRISE ESP_037195_1625 NASA/JPL/Univ. of Arizona)

What on Mars?

August 05, 2014

A piece of Mars: What on Mars is this (the scene is 600×450 m, or 0.37×0.28 mi)? It can be hard to tell. The lines are ridges of windblown dunes or ripples, the dark gray stuff is active sand blowing between the dunes, and the underlying bedrock is pale tan. But if your eyes can’t make sense of it all, just sit back and enjoy the pretty patterns of Mars. (HiRISE ESP_037161_1785, NASA/JPL/Univ. of Arizona)

Small dunes up high, big dunes down low

July 29, 2014

A piece of Mars: This 1018×1352 m (0.63×0.84 mi) dune-covered scene has split topography: the the bottom part is up on a plateau, and the upper part is in a broad valley. The dunes up on the plateau are smaller than the ones in the valley. Why? Probably because there was more mobile dune-building sediment in the valley to begin with: the dunes up high ran out of material and stopped growing, but the ones in the valley kept getting bigger. (HiRISE ESP_036795_1760, NASA/JPL/Univ. of Arizona)

Summery dune

July 22, 2014

A piece of Mars: Last December I blogged about a picture of a sand dune taken in early northern spring. This is the same dune, without frost, now that summer has come to the northern hemisphere and all the frost is gone. It’s quite a difference. Apparently the dunes are controlled by ice in the winter and by the wind in the summer. (HiRISE ESP_035997_2565, NASA/JPL/Univ. of Arizona)

How hills change dunes

July 08, 2014

A piece of Mars: Using dunes to interpret the winds can be a tricky business. Here’s one reason why: most of the dunes here go from the upper left to lower right. But the ones inside the funky oblong crater go from the upper right to the lower left. Why? One of two reasons. Either the rim of the crater rotates the winds that blow inside, or the rim blocks one wind but lets in another that is less effective at making dunes outside. (HiRISE ESP_036934_1915, NASA/JPL/Univ. of Arizona)

Where is Curiosity on her 1 Mars year anniversary?

July 01, 2014

A piece of Mars: Curiosity has been trolling around on Mars for one martian year, so I think it’s time I posted an update on where it is and what it’s seeing. Right now (late June 2014), the rover is rolling across meter-sized ripples, heading south toward Mt. Sharp. In the near future there will be even more impressive ripples, and then finally the terrain will start to grow more interesting. I will post more of these in the months to come. (HiRISE ESP_029034_1750, NASA/JPL/Univ. of Arizona)

In the lee

June 24, 2014

A piece of Mars: This crater (290 m or 950 ft across) is crawling with all sorts of ripples and dunes. The wind mainly blows from the top to the bottom of the frame, and it is responsible for the wonderful textures in the dark gray sand. It has also formed larger, cream-colored ripples. The creamy and dark gray sand have taken turns burying one another, like vines competing for sunlight. (HiRISE ESP_034084_1655 , NASA/JPL/Univ. of Arizona)

Swirly rocks

June 18, 2014

A piece of Mars: Never mind the 4 m (13 ft) boulders that have fallen downslope, or the rippled sandy surfaces here. Look at those bright swirls in the ground. Those are the former interiors of sand dunes, which were trapped and incorporated into the bedrock (like dinosaur bones, but without so much rawr). The wind has been blowing sand around on Mars for a long, long time. (HiRISE ESP_036436_2645, NASA/JPL/Univ. of Arizona)

Whither the wind

June 13, 2014

A piece of Mars: Which way did the wind blow here? You can tell by looking at the dune and its ripples. The slip face (the avalanching slope of the dune) faces downwind, so the strongest wind here mainly blows toward the upper left. But that’s not the whole story, because, like on Earth, martian winds are always shifting. Recent avalanching and some ripples on the slip face show that the most recent wind blew toward the top of the frame. The dune is 267×110 m (876×361 ft). (HiRISE ESP_036393_2650, NASA/JPL/Univ. of Arizona)