Astronomy Picture of the Day
February 5, 2014

Approaching Xiao Zhao (Part II)
Approaching Xiao Zhao (Part II)

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.

Once again, we are taking a look at the Mercurian Impact Crater called Xiao Zhao (whose diameter is approx. 24 Km - such as about 14,9 miles). Xiao Zhao Crater is a relatively young Impact Crater with, as you can very well see here, a prominent Complex Central Peak and a huge System of Hollows (the Bright Rays' System cannot be seen in this picture). This image is pretty similar to the one that we showed you in yesterday's APOD as well as to a few other ones acquired by the NASA - MESSENGER Spacecraft in the past.

The reason of photographing several times the same Feature is in the fact that certain Mercurian Impact Locations (just like Xiao Zhao Crater - and many other Mercurian Craters, all characterized by the presence of Bright Hollows) could slightly change, in time. Given that, through the aforementioned repeated imaging (consider that these kind of pictures are taken months away from one another), the Planetary Scientists that study these frames may be able to identify any (even) extremely slight hint of change, if it has actually occurred, in the Features themselves (in other words: the repeated images of Xiao Zhao and other Mercurian 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 about 9 o'clock of the Crater's Floor.

Date acquired: December, 4th, 2013
Image Mission Elapsed Time (MET): 28472584
Image ID: 5318200
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 10,65° North
Center Longitude: 123,94° East
Solar Incidence Angle: 24,9° (meaning that the Sun, at the time that the picture was taken, was about 65,1° above the imaged Local Mercurian Horizon)
Emission Angle: 32,4°
Sun-Mercury-Messenger (or "Phase") Angle: 44,7°

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 17925) 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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