Astronomy Picture of the Day
July 9, 2013

Dunes (EDM)
Dunes (EDM)

Credits: NASA/JPL/University of Arizona - Credits for the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

While most so-called "Barchan Dunes" (also known as "Crescent Dunes"), both on Earth and Mars, are nearly (---> almost) symmetrical in shape, with two "Horns" pointing Down-Wind, the Dunes that we see in this picture (taken by the NASA - Mars Reconnaissance Orbiter on the date of November 23, 2012) only have one pointy Horn. Their other (---> second) "Horn", in fact, is very rounded and the steep Slipface (such as the smooth Slope located between the Horn and the rounded area that only forms in the sheltered (---> protected) Down-Wind side of the Dune) is offset from the middle.
The lack of symmetry within these Dunes tells us that there is more than one Wind (beside the "Dominant Wind") acting here. The Dominant Wind within this Martian Region blows along the direction of the Horns (both the rounded and pointed ones) - such as from the top-right of the image. On the other hand, another (relatively) strong (but NOT Dominant) Wind, alters the basic Dune-shape and, most likely, this second (weaker than the DominantWind is blowing from the top-left quadrant of the picture, thus causing one Horn to elongate and the Slipface to be offset.

Mars Local Time: 15:44 (Middle Afternoon)
Coord. (centered): 44,715° South Lat. and 331,100° East Long.
Spacecraft altitude: 255,8 Km (such as about 158,851 miles)
Original image scale range: from 25,6 cm/pixel (with 1 x 1 binning) to 51,2 (with 2 x 2 binning)
Map projected scale: 25 cm/pixel
Emission Angle: 1,1°
Phase Angle: 56,1°
Solar Incidence Angle: 57° (meaning that the Sun was about 33° above the Local Horizon at the time the picture was taken)
Solar Longitude: 212,3° (Northern Fall - Southern Spring)
Credits: NASA/JPL/University of Arizona
Additional process. and coloring: Lunar Explorer Italia

This picture (which is a crop taken from a NASA - Original Mars Reconnaissance Orbiter NON-Map Projected CTX b/w frame identified by the serial n. ESP_029660_1350) has been additionally processed and then colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Mars Reconnaissance Orbiter and then looked down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.

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