Astronomy Picture of the Day
February 9, 2014

Volcanism on the Limb
Volcanism on the Limb

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 almost countless gray/whitish bright spots that stand out against the dark Southern Lower Reflectance Plains of Mercury, as they appear in this suggestive image-mosaic made out of three frames taken  by the NASA - MESSENGER Spacecraft on August, 2, 2013 - and approx. 725 Km (such as about 450,225 miles) wide at the top - are a series of Pyroclastic Vents stretching from roughly 60° South Latitude, within the Impact Crater Hesiod, to about 51° South Latitude.

These Vents are believed to have been the points of origin of powerful Explosive Volcanic Eruptions, driven (---> caused) by the action (---> high pressure) of a number of Volcanic Gases - which were trapped, possibly with other molten Materials in the Mercurian Sub-Surface - at the time when they came out. Even though these Features can be found all across Mercury, this specific Region contains one of the largest and known Clusters of Vents of the whole Planet.

Date acquired: August, 2nd, 2013
Images Mission Elapsed Time (MET): 17789351, 17789371, 17789355
Images ID: 4558440, 4558445, 4558441
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 52,65° South
Center Longitude: 329,50° East
Solar Incidence Angle (at the center of the frame): 58,9° (meaning that the Sun, at the time that the picture was taken, was about 31,1° above the center of the imaged Local Mercurian Horizon)
Emission Angle: 59,2°
Sun-Mercury-Messenger (or "Phase") Angle: 28,0°

This picture (which is an Original NASA - MESSENGER Spacecraft's false colors and NON-Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 17973) has been additionally processed, contrast enhanced, Gamma corrected, magnified to aid the visibility of the details and then re-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 outside, towards the Southern Limb 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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