Astronomy Picture of the Day
April 24, 2013

Snorri Crater
Snorri Crater

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 bright, Rayed Impact Crater visible in this image taken by the NASA - MESSENGER Spacecraft, is one of the most prominent that we can find on the Planet Mercury. Named Snorri, after an Icelandic writer and poet, this Impact Crater is approx. 21 Km (such as a little more than 13 miles) in diameter and it was, in fact, discovered after the examination of the images returned by the NASA  - Mariner 10 Spacecraft when it flew by Mercury on September, 21, 1974.

This frame was acquired as part of MDIS's High-Resolution Surface Morphology Base Map. The Surface Morphology Base Map covers more than 99% of Mercury's Surface with an Average Resolution of 200 meters/pixel. Images acquired for the Surface Morphology Base Map typically are obtained at off-vertical Sun Angles (---> high Solar Incidence Angles) and have visible Shadows so to clearly reveal the actual topographic forms/shapes of the imaged Geologic Features.

Date acquired: October, 14th, 2011
Image Mission Elapsed Time (MET): 227045180
Image ID882221
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 9,42° South
Center Longitude: 277,10° East
Resolution: 195 meters/pixel
Solar Incidence Angle: 22,4° (meaning that the Sun, at the time that the picture was taken, was about 67,6° above the imaged Local Mercurian Horizon)
Emission Angle: 51,0°
Sun-Mercury-Messenger (or "Phase") Angle: 73,4°

This image (which is an Original NASA - MESSENGER Spacecraft Map Projected b/w frame published on the NASA - Planetary Photojournal with the ID n. PIA 16993) 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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