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• 1 media/Mars Dust strom.jpg 2016-05-31T08:36:20+00:00 Mars is a Windy Place 27 image_header 2022-02-10T19:05:47+00:00
  
  
  
  Even though it has a thin atmosphere the winds on Mars can be very strong.  By now we assume that most of us know that the reason Matt Damon was left behind on Mars was because of a massive dust storm.  As is pointed out here, that is not fiction.
   

  Mars is infamous for intense dust storms, which sometimes kick up enough dust to be seen by telescopes on Earth.

  “Every year there are some moderately big dust storms that pop up on Mars and they cover continent-sized areas and last for weeks at a time,” said Michael Smith, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

  Beyond Mars’ large annual storms are massive storms that occur more rarely but are much larger and more intense.

  “Once every three Mars years (about 5 ½ Earth years), on average, normal storms grow into planet-encircling dust storms, and we usually call those ‘global dust storms’ to distinguish them,” Smith said.

  It is unlikely that even these dust storms could strand an astronaut on Mars, however. Even the wind in the largest dust storms likely could not tip or rip apart major mechanical equipment. The winds in the strongest Martian storms top out at about 60 miles per hour, less than half the speed of some hurricane-force winds on Earth.

  Focusing on wind speed may be a little misleading, as well. The atmosphere on Mars is about 1 percent as dense as Earth’s atmosphere. That means to fly a kite on Mars, the wind would need to blow much faster than on Earth to get the kite in the air.

  “The key difference between Earth and Mars is that Mars’ atmospheric pressure is a lot less,” said William Farrell, a plasma physicist who studies atmospheric breakdown in Mars dust storms at Goddard. “So things get blown, but it’s not with the same intensity.”

  While dust storms may not be dangerous directly to any future Martians, they can block the sun completely for a while, which is bad if you rely on solar cells for the electricity to run your equipment. In 2007, an earlier generation of rovers, Spirit and Opportunity weathered a major dust storm:
  
  In addition to major, and smaller dust storms, we have observed dust devils that we also see on Earth.  Here is a nice example observed by the Rover Spirit in Gusev Carter in 2005:
  

  A dust devil spins across the surface of Gusev Crater just before noon on Mars. NASA's Spirit rover took the series of images in this spectacular 21-frame animation with its navigation camera on the rover's martian day, or sol, 486 (May 15, 2005).
  
  The event occurred during a period of 9 minutes and 35 seconds beginning at 11:48 a.m. local Mars time, recording the dust devil's progress in a northeasterly direction about 1.0 kilometer (0.62 mile) away from Spirit's perch on the slopes of the "Columbia Hills." The whirlwind was traveling at about 4.8 meters per second (16 feet per second) and covered a distance of about 1.6 kilometers (1 mile).
  
  Contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil. The dust devil is about 34 meters (112 feet) in diameter.
  
  Image credit: NASA/JPL

  And here is a more recent example from 2012, referred to as "The Serpent Dust Devil of Mars" as observed from orbit with the HiRISE camera:
  

  A towering dust devil casts a serpentine shadow over the Martian surface in this stunning, late springtime image of Amazonis Planitia.
  
  The length of the shadow indicates that the dust plume reaches more than 800 meters, or half a mile, in height. The tail of the plume does not trace the path of the dust devil, which had been following a steady course towards the southeast and left a bright track behind it.
  
  The delicate arc in the plume was produced by a westerly breeze at about a 250-meter height that blew the top of the plume towards the east. The westerly winds and the draw of warmth to the south combine to guide dust devils along southeast trending paths, as indicated by the tracks of many previous dust-devils. The dust plume itself is about 30 meters in diameter.

  If you like the look of this image, clicking on this link will allow you download multiple versions in many different resolutions.  There is even a cool video, complete with robot-voice soundtrack(!) which provides more context (and which we would have included if we could have stopped the auto-play).
  
  Even though dust storms may not be that destructive, on the geological scale, over millions of years to of time, dust can have a profound effect on sculpting the landscape. Over such timescales, windblown sand can wear down rocks by sandblasting them.  If the rocks are soft, the shapes that emerge are streamlined shapes that are parallel to the predominant wind direction.  Such feature are called yardangs and we find them on Earth as well as on Mars.  Here is an example of yardangs within Valles Marineris (Note: at that link you'll also find various sizes of the image as well as a video with more explanation).
  
  

  The slightly curving, sublinear bright terrain is composed of yardangs. Yardangs are portions of rock that have been sand blasted into long, skinny ridges by saltating (or bouncing) sand particles blowing in the wind.

  So far we concentrated on dust and mentioned that dust can actively erode rocks.  Over geological time we would then expect to see this erosion product, namely sand. And when there is a lot of sand there may also be dunes.  And in fact sand dunes are among the most common land forms on Mars.  Dune fields are often located within craters, though large dune fields are also found within Valles Marineris.  This image show the locations of dunes:
  
  
  
  Dunes quite often occur as large dune fields.  This is an example of a dune field named Nili Patera.  This is what it looks like from space.
  
  
  I turns out these dunes are not static and un-moving.  By taking multiple images of the same dunes (ones again with the HiRISE) we know that dunes can still be active.  Here is composite image of dunes, complete with line drawing illustrating the changes.  Some of the ripples on the dunes had migrated by as much as 2 m over the span of 15 weeks.

  Three pairs of before and after images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter illustrate movement of ripples on dark sand dunes in the Nili Patera region of Mars.

  The three images on the left are excerpts from a June 30, 2007, observation (late autumn at the site). The three on the right are of the same ground observed 15 weeks later, on Oct. 13, 2007 (winter at the site). Ripple crests discernable in the central portion of each image are diagrammed in the lower right portion of each image, with blue lines highlighting the largest changes. White scale bars in the bottom right of each of the six images are 20 meters (66 feet) long. North is toward the top.

  The video that goes along with it is well worth watching (we would include it if we could force it to not not auto-play).
  
  We actually know very well what these dunes look like from the surface as rovers have been visiting dunes for the last few years.  Below is a self-portrait of the Curiosity rover at its sampling location at Namib dune.  And here is a link to a stunning YouTube 360 panorama of a 5-meter high dark sand dune as well as some more information.