Astronomy Picture of the Day - powered by LUNEXIT.IT

This image, taken with the Narrow Angle Camera (NAC) onboard NASA - MESSENGER Spacecraft, now orbiting the Planet Mercury, shows a pair of (possibly Secondary) Crater Chains. These kind of Surface Features are formed, for instance (and like our NASA Friends suggest for the case in point), when Ejecta (meaning rocks and boulders belonging to the Impacted Celestial Body) deriving from a Primary Impact, are thrown up and outward from the Growing Cater Cavity; as the Ejecta fall back onto the Surface, they can form Chains of Secondary Craters that - sometimes - may also overlap.

However, another possibility for these specific Surface Features to form, is when a flock of Meteorites (or maybe just a huge one that broke into pieces during the fall, or right before the impact) strikes the Surface of a Celestial Body according to a so-called Straight Sequential Impact Line (in other words, just imagine a series of Impactors striking the Surface of Mercury in sequence, one after the other, with all of them having almost identical Impact Angles and all of them impacting in accordance to a - relatively - straight line). One last (but certainly not the least...) possibility for a Crater Chain (like the one we are showing you in today's APOD) to form, is because of a Cometary Impact. In this specific case, as we have said hereabove, our NASA Friends, once all the above possibilities were given, opted for a Secondary Craters Chain, and we, as IPF, may also agree with that (even though that option is certainly NOT our first choice). Anyway, what was the exact scientific reason that the decision made by the NASA Scientists for this case was based on, unfortunately, it is impossible for us to say.

This image was acquired as part of MDIS's High-Resolution Surface Morphology Base Map. The Surface Morphology Base Map will cover more than 90% of Mercury's Surface with an average resolution of approx. 250 meters/pixel (0,16 miles/pixel or 820 feet/pixel).
Images acquired for the Surface Morphology Base Map typically have off-vertical Sun Angles (such as High Solar Incidence Angles, meaning low Sun over the Local Horizon ) and visible shadows, so as to reveal clearly the topographic form of the photographed Geologic Features.

Date acquired: October 28, 2011
Image Mission Elapsed Time (MET): 228324766
Image ID: 943677
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 2,94° North
Center Longitude: 160,5° East
Resolution: 193 meters/pixel
Scale: this frame is about 100 Km (approx. 62 miles) across
Solar Incidence Angle: 87,3° (meaning that the Sun is about 2,7° above the Local Horizon)
Emission Angle: 17,3°
Sun-Mercury-MESSENGER (or "Phase") Angle: 104,7°

This frame has been 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.