Astronomy Picture of the Day
April 21, 2014

Fonteyn Crater
Fonteyn Crater

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.

Most Meteorites, as you know, are pieces (---> fragments) derived from a larger Asteroid that disintegrated in the Atmosphere during the fall, or when it still was in Space (maybe because it unsuccessfully crossed the Roche Limit of a given Celestial Body), or - last but not least - because it impacted another Celestial Body; on Earth, about 130 Meteorites have been linked to an origin from impacts which have occurred on the Planet Mars, and nearly 200 of them are believed to have originated from impacts occurred on our Moon. However, no Meteorite - so far - has been convincingly shown to have come from Mercury. Impact Cratering Events on Mercury may actually blast large quantities of Material off the Surface and then into Space, but it is much more difficult for such Material to move into an orbit that could intersect the one of Earth. In 1992, Stan Love and Klaus Keil published a study describing the likely characteristics of a Mercurian Meteorite and a recent re-look at the topic of Meteorites from Mercury, by Drr Will Vaughan and Jim Head, pointed out that the dynamics of ejection are such that the most likely locations for Source Craters (---> source of Impacts which might have been powerful enough to launch Material into Space and towards other Celestial Bodies) on Mercury are in Regions centered in between 90° and 270° East Longitude.


Fonteyn Crater, shown in today's APOD, is a relatively fresh and approx. 29-Km (such as a little more than 18 miles) diameter Impact Structure centered at about 33° North Latitude and 95° East Longitude, such as within the probable zone noted by Vaughan and Head. Fonteyn Impact Crater has a somewhat asymmetrical pattern of Bright Rays, suggesting that it formed in an Oblique Impact, which may favor the ejection of Material at speeds greater than the Escape Velocity. Could the Fonteyn Impact have launched Material that has already fallen on Earth, or is on its way? Maybe. And maybe not. But, sometime in the Future (probably a very distant one), we could find a believable and fairly convincing answer even to this hard and intriguing question...


This mosaic (which is approx. 730 Km - such as about 453,33 miles - wide) is a portion of the MDIS's High-Resolution Surface Morphology Base Map. The Surface Morphology Base Map covers more than 99% of Mercury's Surface with an average resolution of 200 meters/pixel. Images acquired for the Surface Morphology Base Map typically are obtained at off-vertical Sun Angles (i.e., High Incidence Angles) and have visible shadows so as to reveal clearly the Topographic Form of Geologic Surface Features.


Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)


This picture (which is an Original NASA - MESSENGER Spacecraft's b/w and NON Map-Projected image-mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 18212) 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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