Astronomy Picture of the Day
September 18, 2014

Double Impact on the Northern Plains of Mercury
Double Impact on 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.

The Surface of Mercury, as you know, is dominated by Impact Craters, so it is not surprising that every so often one Crater forms atop another. In this image, taken by the NASA - MESSENGER Spacecraft on July, 10, 2014, a small and very old Unnamed Crater formed close to the Southern Margin of Mercury's Northern Volcanic Plains, before being superposed by a slightly larger and deeper Crater (approx. 10 Km - such as about 6,21 miles - across). and this second Impact removed over a third of the smaller, pre-existing Crater.

Yet both Impact Craters show evidence of post-formation modification, notably where their Walls meet their Floors. For example, a Hill lies at the base of the right-hand-side Wall of the larger Unnamed Impact Crater. This Surface Feature is, most likely, a Landslide Deposit that formed when some Material (Rocks and Dust) slumped off the Wall (possibly because of the occurrence of a phenomenon of Gravity Wasting or, maybe, when the Shock Waves coming from another Impact which occurred nearby passed through these two Craters). Out of curiosity, a small and white Surface Feature with a set of whitish Striations above it - most likely a Boulder that rolled down the Western Slopes of the larger Impact Crater -, is clearly visible at about 8 o'clock of the Crater itself. This interpretation, in our opinion, as IPF, seems to be confirmed by the very clear - and easy to see - Surface Features that are visible near and right on the Edge of the larger Crater, still at about 8 'o clock of its Rim.

Date acquired: July, 10th, 2014
Image Mission Elapsed Time (MET): 47351839
Image ID: 6659618
InstrumentNarrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 52,30° North
Center Longitude: 31,60° East
Solar Incidence Angle (at center frame): 54,1° (meaning that the Sun, at the time that the pictures were taken, was about 35,9° above the imaged Local Mercurian Horizon)
Emission Angle (at center frame): 28,3° (meaning that the Spacecraft was far away from being - even just almost - perpendicular to the imaged Surface at the time when the picture was taken)
Sun-Mercury-Messenger (or "Phase") Angle (at center frame): 45,2°

This picture (which is a crop taken from an Original NASA - MESSENGER Spacecraft's b/w and NON Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 18708) 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 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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