Astronomy Picture of the Day
November 17, 2013

Bright Crater, Dark Surface (EDM)
Bright Crater, Dark Surface (EDM)

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.

Today's APOD is an Extra Detail Magnification (or "EDM" for short) which has been taken from image-mosaic obtained by putting together 3 (three) NASA - MESSENGER Spacecraft's frames; it shows us, with remarkable detail, an interesting Unnamed Impact Crater which is located to the North of the Mercurian Impact Crater Couperin. Although this specific Unnamed Impact Crater is relatively small - consider that its only about 6 Km (such as about 3,72 miles) in diameter -, its bright  Rays' System cause it to stand out prominently in the context of a Local (or even Regional) view of the Planet Mercury.

In other words, this Unnamed Imapact Crater its quite peculiar - in a way - not just because its Interior (---> Floor) and its Rays are particularly bright (which is a fact), but rhather because its bright Rays's System, tends to fade (actually, it does fade and quickly disappers) into the very dark background of the Crater's Surroundings; Surroundings which, as you might have already imagined, are mostly made of (or even covered by) the so-called "Low Reflectance Material" (or "LRM" for short).

One possible explanation of the LRM can be found, in our opinion, as IPF, in the fact that (almost) the whole Surface of Mercury has been litterally "cooked", in a few billions of years, as a consequence of the so-called "Space Weathering", such as the darkening - which goes, in time, from a very dark red, to a deep black color - of the Surface of a Celestial Body that is caused by a continuous "rain" of charged particles (like the ones forming, for instance, the Solar Wind). If this hypothesis - and no matter how unlikely it could sound to you at first - were even just partially correct, we should then assume that the heavy meteoritic bombardment that Mercury has suffered in its History, could and should have taken place quite a long time (and we are talking about, again, of some billions of years) after the formation of the Planet itself. And this circumstance, if proven to be correct, would also change the entire History of the Solar System, as we know it.

In the future, maybe, we shall learn more about this and we will discuss the subject again. Now, this is just "Food for Thoughts", for you all... 

Date acquired: October, 19th, 2013
Images Mission Elapsed Time (MET): 24470528, 24470520, 24470516
Images ID: 5033545, 5033543, 5033542
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 35,86° North
Center Longitude: 207,90° East
Solar Incidence Angle: 37,1° (meaning that the Sun, at the time that the picture was taken, was about 52,9° above the imaged Local Mercurian Horizon)
Emission Angle: 9,1°
Sun-Mercury-Messenger (or "Phase") Angle: 41,6°

This frame (which is a crop taken from an Original NASA - MESSENGER Spacecraft's false-colors and Map-Projected image-mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 17678) has been additionally processed, contrast enhanced, magnified to aid the visibility of the details, Gamma corrected 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 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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