Astronomy Picture of the Day
February 4, 2014

Approaching Xiao Zhao (Part I)
Approaching Xiao Zhao (Part I)

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 Mercurian Impact Crater shown in today's APOD is called Xiao Zhao (whose diameter is approx. 24 Km - such as about 14,9 miles), and it is a relatively young Impact Crater, with a prominent Complex Central Peak and a huge System of Hollows and Bright Rays (barely visible here).

This image is extremely similar to a few other ones acquired by the NASA - MESSENGER Spacecraft in the past, and the reason is in the fact that certain Surface Impact Features, just like Xiao Zhao Crater - as well as many other similar Mercurian (Impact) Locations, all characterized by the presence of Bright Hollows - are and will be repeatedly imaged by the MESSENGER Spaceraft to look for any (even) extremely slight hint of change (in other words: the repeated images of Xiao Zhao and other Impact Craters, are and will be taken in order to verify if the process that leads to the creation of the Hollows is - or is not - still ongoing on Mercury).

Just out of curiosity, please note the extremely dark "Spot" (which is NOT a shadow, but - maybe - a relatively large area covered by Low Reflectance Material) that is located to the South/West of Zhao's Complex Central Peak, and going from about 6 to 9 o'clock of the Crater's Floor.

Date acquired: December, 19th, 2012
Image Mission Elapsed Time (MET): 264389643
Image ID: 3167776
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 10,64° North
Center Longitude: 123,90° East
Solar Incidence Angle: 20,3° (meaning that the Sun, at the time that the picture was taken, was about 69,7° above the imaged Local Mercurian Horizon)
Emission Angle: 40,8°
Sun-Mercury-Messenger (or "Phase") Angle: 58,5°

This picture (which is a crop taken from an Original NASA - MESSENGER Spacecraft's b/w and Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 16856) has been additionally processed, contrast enhanced, Gamma corrected, magnified to aid the visibility of the details 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 outside, towards the 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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