Astronomy Picture of the Day
November 15, 2014

Inca City, from MRO (1)
Inca City, from MRO (1)

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

At every Martian Winter, a Layer of Carbon Dioxide IceCO2 or, also , Dry Ice — condenses in the Southern Polar Regions of Mars, forming a so-called "Seasonal Polar Cap" which is less than 1 meter deep. Early in the Spring, the Ice Layer begins to sublimate (---> going directly from a Solid State to a Gaseus State) both from the top and bottom. In time, the Ice Gas Pressure builds up, until a weak spot in the Ice Layer ruptures; then the Gas rushes out and, as it escapes, it also erodes a bit of the Surface.

Fine Particles are carried by the escaping Gas to the top of the Ice and then they fall out in "Fan-shaped Deposits". The direction of the Fans shows us the direction either of the Wind, or of the Slope where the Fan is located on. In case there is no Wind blowing, a Dark Blotch settles around the weak spot where the Gas escaped from.

This Region of the Red Planet is known informally as Inca City, and it has a series of extremely distinctive Ridges. On the Floor between the Ridges there are Radially-Organized Channels, known colloquially as "Spiders" (and more formally known as "Araneiform Surface Features"). The Channels have been carved in the Surface over many years by the escaping pressurized Gas and, at every Spring, they widen just a bit.  This was the first image acquired by the NASA - Mars Reconnaissance Orbiter after the Sun rose on Inca City, marking the end to the Polar Night. A few Fans are visible emerging from the Araneiform Surface Feastures.

Mars Local Time: 16:23 (Middle Afternoon)
Coord. (centered): 81,447° South Lat. and 295,885° East Long.
Spacecraft altitude: 257,8 Km (such as about 160,093 miles)
Original image scale range: 51,6 cm/pixel (with 2 x 2 binningso objects ~ 1 meter and 55 cm across are resolved
Map projected scale: 50 cm/pixel
Emission Angle: 17,8°
Phase Angle: 103,8°
Solar Incidence Angle: 89° (meaning that the Sun was about above the Local Horizon at the time the picture was taken)
Solar Longitude: 173,7° (Northern Summer - Southern Winter)
Credits: NASA/JPL/University of Arizona
Additional process. and coloring: Lunar Explorer Italia

This picture (which is a NASA - Original Mars Reconnaissance Orbiter b/w and NON Map-Projected frame identified by the serial n. ESP_037626_0985) has been additionally processed, reduced in size to fit the page, contrast enhanced, Gamma corrected, 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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