Astronomy Picture of the Day
August 4, 2014

Mercurian Secondary Craters' Field
Mercurian Secondary Craters' Field

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.

This image is one of the Highest Resolution Images taken by the NASA - MESSENGER Spacecraft to date (---> so far). It features a Field of (mainly) Secondary Complex Craters which are located in Mercury's Northern Smooth Plains. The Secondary Craters are formed by the Re-Impact (---> fall) of Rocky Debris that came (derived) from the formation of one (or more) larger Primary Impact Crater/s. The largest Secondary Craters visible in this image are roughly a few hundred meters across and, if you look closely, you will be able to see some small Impact Craters that are only tens of meters across (and almost all of these ones are just Simple Secondary Impact Craters - with a few tiny Primary ones).

This image was acquired as part of the MDIS Low-Altitude Imaging Campaign. During MESSENGER's Second Extended Mission, the Spacecraft shall make a progressively closer approach to Mercury's Surface than at any previous point in the Mission, thus enabling the acquisition of High-Spatial-Resolution Data. For Spacecraft altitudes below the 350 Km (such as about 217,35 miles), the NAC images are acquired with pixel scales ranging from 20 meters to as little as 2 meters.

On July, 25, 2014, the NASA - MESSENGER Spacecraft moved closer to Mercury than any Spacecraft has ever done before, dropping to an Altitude of only about 100 Km (such as approx. 62,1 miles) above the Planet's Surface. By August, 19, 2014, the Minimum Altitude will be cut in half, to only about 50 Km (such as approx. 31,05 miles). Then, the  NASA - MESSENGER Spacecraft will execute three more Orbit-Correction Maneuvers in order to delay the end of the Mission up to the late March of the AD 2015.

This frame covers an area of approx. 3 Km - such as about 1,863 miles - across.

Date acquired: June, 11th, 2014
Image Mission Elapsed Time (MET): 44779109
Image ID: 6477542
InstrumentNarrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 69,84° North
Center Longitude: 48,47° East
Solar Incidence Angle (at center frame): 79,4° (meaning that the Sun, at the time that the pictures were taken, was about 10,6° above the imaged Local Mercurian Horizon)
Emission Angle (at center frame): 0,1° (meaning that the Spacecraft was almost perpendicular as to the imaged Surface at the time when the picture was taken)
Sun-Mercury-Messenger (or "Phase") Angle (at center frame): 79,6°

This picture (which is an Original NASA - MESSENGER Spacecraft's b/w and NON Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 18630) 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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