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• THE LUNAR EXPLORER ARCHIVES
• MOON
• MARS
• SOLAR SYSTEM
• DEEP SKY

A R C H I V E S

This mosaic of NAC images shows the Impact Crater Hokusai, located on the Planet Mercury at a Latitude of approx. 58° North. Hokusai (that here is visible near the Upper Limb of Mercury, at about one o' clock), shows an impressive System of Rays, which extend as much as a thousand kilometers (such as more than 600 miles) across the entire Planet and are they are the longest that have yet been identified on Mercury.
These Rays are formed when an Impact excavates Material from beneath the Surface and then throws it outward from the newly created Crater. These Bright Rays, consisting of both Ejecta and Secondary Craters (which form when the ejected material re-impacts the Surface), slowly begin to fade as they are exposed to the harsh Space Environment. Mercury and other airless Planetary Bodies are being constantly bombarded with Micrometeoroids and Energetic Ions (think about, for instance, to the Energetic Particles forming the Solar Wind), both concurring to produce an effect known as "Space Weathering".

Craters with Bright Rays are thought to be relatively young, because the Rays are still visible, and this fact indicates that they have suffered less exposure to the aformentioned Space Weathering Processes than Impact Craters which lack Rays; well, such a consideration is basically correct BUT, as IPF, we have to say and underline, however (and just for the sake of clarity), that it should also be considered the fact that the creation of a System of Rays emanating from a certain (given) Impact Crater depends, among other things, on the existence (and simultaneous concurrence) of a number of additional circumstances, whose lack may very well lead to the formation of a "Rayless" (or an almost "Rayless") Impact Crater.

In other words: the lack of Rays IS NOT (and CANNOT be considered) a 100% reliable indicator that a specific Impact Crater is "old"!.

Although the extent of some of Hokusai's Rays has been determined, the images acquired during the NASA - MESSENGER Spacecraft's 3rd Fly-By of Planet Mercury were not good enough to show all of them. However, during the NASA - MESSENGER Spacecraft's Orbital Observations, which have started in March 2011, the Mercury Dual Imaging System (MDIS) has already acquired high-resolution color images that are fit to cover almost the entire Surface of Mercury. Afterwards, when the Global Color Map of Planet Mercury is complete, then Scientists shall finally be able to better understand the effective extent of the unbelievable Systems of Rays emanating from Hokusai Crater, as well as the characteristics and extent of other System of Rays emanating from quite a few other young Mercurian Impact Craters, which are now going to be mapped for the first time in History.

Date Acquired: October, 6th, 2008
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Scale: the diameter of the Planet Mercury is of about 4880 Km (such as approx. 3030,48 miles) and Hokusai Crater has a diameter of approx. 95 Km (such as about 58,995 miles)