Astronomy Picture of the Day
May 5, 2013

Around Caloris Basin...
Around Caloris Basin...

Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington and Dr Paolo C. Fienga/LXTT/IPF for the additional process. and color.

The Plains that encircle the huge Caloris Basin on Mercury, are, from a geological point of view, extremely complex, and today's APOD tries to highlight some of the kilometer-scale Knobs that surround much of the Basin and which are thought to be, by Planetary Scientists, Blocks of Material ejected during the Caloris Basin-forming Event. This area, which is located within Tir Planitia, has also been subjected to the so-called "Compressional Stress" (*), which resulted in the formation of Scarps that cut across the whole scene. Unraveling the complex sequence of Events that occurred in this Region (which includes, among others, the deposition of Ejecta, the verification of possible Volcanic-related Resurfacing and Tectonic Deformation), will be aided by the High-Resolution Targeted Images to be collected during the NASA - MESSENGER Spacecraft second Extended Mission.

(*): in Geology, the term Compression refers to a Set of Stresses directed toward the center of a Rock Mass. Compressive Strength refers to the Maximum Compressive Stress that can be applied to a certain Material before its failure occurs. When the Maximum Compressive Stress is in an Horizontal Orientation, then Thrust Faulting can occur, resulting in the shortening and thickening of that portion of the Crust that was involved by the stressing action. On the other hand, when the Maximum Compressive Stress is in a Vertical Orientation, a section of Rock will often fail in Normal Faults, horizontally extending and vertically thinning a given Layer of Rock. Sometimes, extremely powerful Compressive Stresses can also result in the Folding of Rocks. However, because of the large magnitudes of Lithostatic Stress present in Tectonic Plates, the Tectonic-scale Deformation is always subjected to Net Compressive Stress.

Date acquired: April 5th, 2013
Image Mission Elapsed Time (MET): 7472448
Image ID: 3825184
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 4,31° North
Center Longitude: 185,60° East
Resolution: 61 meters/pixel
Solar Incidence Angle: 73,6° (meaning that the Sun, at the time that the picture was taken, was about 16,4° above the imaged Local Mercurian Horizon)
Emission Angle: 40,8°
Sun-Mercury-Messenger (or "Phase") Angle: 114,1°

This picture (which has been cropped from an Original NASA - MESSENGER Spacecraft b/w frame published on the NASA - Planetary Photojournal with the ID n. PIA 17025) 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 - MESSENGER Spacecraft and then looked down, towards the Surface of Mercury), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among other things, the existence of different Elements (Minerals) present on the Surface of Mercury, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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