Astronomy Picture of the Day
September 8, 2014

Fresh Crater and Crater Chains in the Northern Plains of Mercury
Fresh Crater and Crater Chains in the Northern Plains of Mercury

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.

This small, bright Impact Crater (see the lower left - Sx - side of the image-mosaic) is located in the Northern Plains of Mercury, to the South/East of the large Impact Crater Stieglitz. Even though this Impact Crater it is just one of the many found in the approx. 2-to-5 Km (such as about 1,242-to 3,105 miles) size range in this picture, most of the others clearly belong to (---> are members of) a Surface Feature commonly known as "Crater Chains".

The Crater Chains are made by Impact Craters which were created in quick succession because, for instance, the Impactor was fragmented, or, maybe, because they simply were the result of Sequentially-aligned Secondary Impacts. However, the bright Impact Crater visible in the Western portion of the image-mosaic stands out from its surroundings for two reasons: first, its (kind of bizarre-looking) Morphology and, second, to its (always relatively speaking) freshness.

The three images forming this mosaic were acquired by the NASA - MESSENGER Spacecraft on July, 4, 2014, as part of the so-called MDIS's Minimum-Phase-Angle Color Campaign. Near the North Polar Regions of Mercury, the Solar Incidence Angle is always fairly high, because the Sun is, on the other hand, always quite low on the Local Horizon. The Minimum-Phase-Angle Color Campaign acquires images under conditions that tend to minimize the Shadows cominf from the Vertical Reliefs by looking at the Surface as nearly as possible from the same direction as the Sun's illumination comes from (thus reducing the Phase Angle to a very minimum). The images forming the mosaic were acquired through five of the WAC's Narrow-Band Color Filters (like it is done for all the Regions located at Latitudes that are higher than 60° North) and at an average Resolution of 500 meters/pixel. The Minimum-Phase-Angle Color Campaign began, just out of curiosity, in March 2013.

Date acquired: July, 4th, 2014
Images Mission Elapsed Time (MET): 46773193, 46773184, 46773190
Images ID: 6618773, 6618770, 6618772
InstrumentWide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 68,82° North
Center Longitude: 71,79° East
Solar Incidence Angle (at center frame): 73,9° (meaning that the Sun, at the time that the pictures were taken, was about 16,1° above the imaged Local Mercurian Horizon)
Emission Angle (at center frame): 45,8° (meaning that the Spacecraft was far from being perpendicular to the imaged Surface at the time when the picture was taken)
Sun-Mercury-Messenger (or "Phase") Angle (at center frame): 28,0°

This picture (which is an Original NASA - MESSENGER Spacecraft's false colors and Map-Projected image-mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 18701) 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 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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