Astronomy Picture of the Day
December 22, 2012

On the Edge of Caloris
On the Edge of Caloris

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.

Today's APOD image highlights the velvety texture that surrounds several Volcanic Vents located near the Rim of the huge Impact Basin known as Caloris Basin, on Mercury. This (apparently) soft texture, like freshly fallen snow, is formed by the emplacement of tiny beads of Lava that were explosively erupted and then quenched and solidified just before they reached the Surface. This diffuse Deposit heavily blankets several Impact Craters and older Vents, while it becomes thinner as long as it goes farther away from the Source of the Eruption. A large amount of the typical Mercurian Surface Features known as "Hollows" is also very well visible on the Rims of a number of Unnamed (and relatively modest in size) Impact Craters. This whole scene is approx. 106 Km across.

Date acquired: November, 17th, 2012
Image Mission Elapsed Time (MET): 261627279
Image ID: 2971208
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 22,03° North
Center Longitude: 146,4° East
Resolution: 54 meters/pixel
Solar Incidence Angle: 39,1° (meaning that the Sun, at the time that the pictures were taken, was about 50,9° above the imaged Local Mercurian Horizon)
Emission Angle: 61,4°
Sun-Mercury-Messenger (or "Phase") Angle: 90,9°

This picture (which is an Original NASA - MESSENGER Spacecraft b/w frame published on the NASA - Planetary Photojournal with the ID n. PIA 16627) 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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