Astronomy Picture of the Day
January 9, 2016

Between Arabia Terra and Terra Meridiani
Between Arabia Terra and Terra Meridiani

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

In this really interesting and also suggestive VIS image, taken by the NASA - Mars Odyssey Orbiter on May, 4th, 2006, and during its 19.458th orbit around the Red Planet, we can see, once again, a small part of the Dusty Plains of the Martian Region known as Arabia Terra, in a peri-Equatorial Area located near the Margin of Terra Meridiani.

Arabia Terra is a large Upland Region, densely cratered, dusty, and heavily eroded, which is located in the Northern Hemisphere of Mars (mostly in the so-called Arabian Quadrangle). This battered Topography (not very well visible here) indicates a great age, and, in fact, Arabia Terra is presumed to be one of the oldest Terrains of Mars. It covers as much as 4500 Km at its longest extent, and it is centered roughly at 19° 79' North Lat. and 30° 00' East Long., with its Eastern and Southern Regions rising higher than (approx.) 4 Km as to the North/Western ones. 

Arabia Terra contains many interesting Surface Features and, for instance, there are some good examples of olda and Unnamed Impact Craters and at least one Winstreak in the area. Quite a lot of Mounds and Buttes can be found on the Floor of many Unnamed Impact Craters and all these Surface Features (such as the Mounds and Buttes, which are basically small and flat-topped Hills - not visible here) show the existence of Layers. The cause, for these Layers, is still unknown, but we do know that Layering can be caused, among other things, by Volcanic and/or Aeolian Processes as well as by the occurrence of a phenomenon of Underwater Deposition of Materials (i.e.: sediments).

Talking about other interesting Surface Features of this Region, we have to notice that Dark Slope Streaks (of course not visible here) have been observed inside the Tikhonravov Basin: a large and widely eroded Impact Crater located, obviously, in the Arabian Quadrangle. These (sometime even multicolored) Streaks usually appear on steep Slopes and (let's say often, but NOT always!) they can change their shape, texture and color over time. At first (such as when they are recent/just formed) they appear like Dark Striations (mostly dark brown and black); then, in time, they may turn to a lighter (i.e.: light brown-yellow /orange) color, probably because of the deposition, all over them, of fine, light orange-colored Dust that falls, like rain, from the lower strata of the Martian Atmosphere.

These Streaks, like some Planetary Scientists say, may also form because of Dust that rapidly moves Downslope (just like Snow Avalanches do on Earth) because of the occurrence, for instance, of slight to moderate vibrations of the Surface (perhaps due to Residual Seismic Activity or to the occurrence of a - relatively close - Meteor Impact) as well as to the verification of a phenomenon known as Gravity Wasting. Last, but not least, the occurrence of a powerful Aeolian Action, as the cause of Dust Avalanches (and Windstreaks, like we can see here) that, afterwards, ends up by forming the Slope Streaks, cannot be axcluded.

Just out of curiosity, Arabia Terra was so officially named after a corresponding Albedo Feature seen on a map of Mars made by the Italian Astronomer Giovanni Schiaparelli (who named this Region after the Earthly Arabian Peninsula). A deeper research about Arabia Terra was undertaken in the AD 1997 and one of its early steps was made by better defining the individuality of the whole Arabian Province as to the other surroundings Regions.

Latitude (centered): 1,40553° North
Longitude (centered): 1,88038° East
Instrument: VIS

This image (which is an Original Mars Odyssey Orbiter falsely colored and Map-Projected frame published on the NASA - Planetary Photojournal with the ID n. PIA 20232) has been additionally processed, magnified to aid the visibility of the details, contrast enhanced an sharpened, Gamma corrected and then re-colorized in Absolute Natural Colors (such as the colors that a normal human eye would actually perceive if someone were onboard the NASA - Mars Odyssey 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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