Astronomy Picture of the Day
October 7, 2012

Northern Dunes
Northern Dunes

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

This NASA - Mars Reconnaissance Orbiter "HiRISE" image shows a portion of a Dunefield where many large "Barchan" (meaning "Crescent-shaped"), a few "Barchanoid" (meaning a "Non uniformly Crescent-shaped") and some smaller Dome-shaped Sand Dunes can be seen. The Dunefield that contains all these types of Sand Dunes is located in the Northern Regions of Mars and in a specific place where the first significant changes occurring to Sand Dunes was reported on the Red Planet (in the AD 2008). That study made by Dr Bourke (et al.) used a time series of NASA - Mars Global Surveyor (MGS), Mars Orbiter Camera (MOC) images taken over a period of 3 Martian Years (which are equivalent to 6 Earth Years) and showed that 2 (two) approx. 20 meter-wide Dome Dunes disappeared while a third one shrank by an estimated 15%.
Now, the HiRISE image here confirms that the first two Sand Dune studied by Dr Bourke no longer exist but, interestingly, it also suggests that the Sediment removal is still ongoing, since the third Dune has dramatically reduced its volume. On the other hand, it must be noticed and underlined that this "Dune-Changing Process" does not occur in a uniform and generalized way (at least in this specific location), since many of the other large Dunes present in the Dunefield do not show any (apparent/obvious) change; however, more time and some more precise measurements (fit to display evidence of the occurrence of an actual change of the larger Dunes, either in their shape, or their position) are needed in order to achieve a more substantiated conclusion.

In addition to that, we should also consider that it is even possible that the stability of all the other larger Dunes present in the Dunefield might be caused by the circumstance that the Sediment existing inside them is now (let us say "at present time"...) unavailable for removal, due to Induration (meaning that said Sediment became too hard to be blown away by just a simple, even though quite strong sometime, Aeolian Action, but in a future - maybe as a consequence of a dramatic variation in the Surface Temperature of this Region of Mars - its physical conditions could change again, and therefore make it fit to be remodeled, removed or, maybe, totally dispersed).

In the end, the change observed in the small Dome-shaped Dunes indicates, once and for all, that certainly not all Dunes on Mars are effectively and permanently stabilized and immobile, as it was erroneously believed for a long time.

Mars Local Time: 14:10 (Early Afternoon)
Coord. (centered): 76,182° North Lat. and 95,300° East Long.
Spacecraft altitude: 318,0 Km (such as about 198,8 miles)
Original image scale range: 63,6 cm/pixel (with 2 x 2 binning) so objects ~ 1 mt and 91 cm across are resolved
Map projected scale: 50 cm/pixel
Emission Angle: 2,8°
Phase Angle: 62,5°
Solar Incidence Angle: 60° (meaning that the Sun was about 30° above the Local Horizon at the time the picture was taken)
Solar Longitude: 47,6° (Northern Spring- Southern Autumn)
Credits: NASA/JPL/University of Arizona
Additional process. and coloring: Lunar Explorer Italia

This picture (which is a NASA - Original Mars Reconnaissance Orbiter EDM color frame identified by the serial n. PSP_007726_2565) 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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