Mercury 2010 Photo Compilation by Messenger

As 2010 comes to a close, the MESSENGER spacecraft is less than three months from becoming the first ever to enter orbit about Mercury. The coming year 2011 promises to be a historic one for the MESSENGER mission and for the exploration of the Solar System more generally. As we await turning the page on the calendar, let's look back at 12 image highlights from this year:

* January: Honoring Haitian Painter Benoit and American Photographer Lange
* February: Spectacular Color... with Better Yet to Come
* March: Rachmaninoff in Concert with Recently Named Craters on Mercury
* April: How Mercury's Copland Received Its Name
* May: Painting a Wave of Rays
* June: The Complex Geology of Geddes Crater
* July: Debussy and Its Hundreds of Miles of Rays
* August: Earth and Moon from 114 Million Miles
* September: Young Volcanism on Mercury
* October: Looking Toward Mercury's Horizon
* November: Mercury's Vast Expanses of Smooth Plains
* December: The Impressive Rays of Hokusai

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The Rays of Hokusai Crater

This mosaic of NAC images shows the impact crater Hokusai, located on Mercury at a latitude of 58° North. The crater has an impressive system of rays, which extend as much as a thousand kilometers (more than 600 miles) across the planet and are the longest that have yet been identified on Mercury.

Such rays are formed when an impact excavates material from beneath the surface and throws that material outward from the crater. These bright rays, consisting of both ejecta and secondary craters that 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, producing an effect known as space weathering. Craters with bright rays are thought to be relatively young because the rays are still visible, indicating that they have had less exposure to such weathering processes than craters that lack rays.

Although the extent of some of Hokusai's rays have been determined, images acquired during MESSENGER's three Mercury flybys have not yet shown all of Hokusai's rays. During MESSENGER's orbital observations, which will begin in March 2011, MDIS will acquire high-resolution color images of Mercury's entire surface. This global color map will allow the full extent of the extensive systems of rays emanating from Hokusai and other young craters to be mapped for the first time.

Date Acquired: October 6, 2008
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Scale: The diameter of Mercury is 4,880 kilometers (3030 miles). Hokusai has a diameter of 95 kilometers (59 miles)

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Long Scarp

Extending from the left edge of this image diagonally toward the lower right corner is a long scarp (cliff) face. This scarp runs through a large ancient crater in the center of the frame and was seen for the first time during MESSENGER's second Mercury flyby. Planetary geologists use the Latin term "rupes" for scarps on Mercury. Scarps such as this one have been identified all over the planet. The presence of many long and high scarps suggests a history for Mercury that is unlike that of any of the other planets in the Solar System. These giant scarps are believed to have formed when Mercury's interior cooled and the entire planet contracted slightly as a result, causing the surface rocks to fracture and some blocks of crust to thrust over others along great faults. Determining the geometry of such scarps on Mercury and information on the times that deformation occurred can thus be used to understand the thermal history of the planet. Next year, when the MESSENGER spacecraft is in orbit around Mercury, MDIS will acquire for the first time global imaging coverage of Mercury's surface with lighting conditions optimal for identifying such scarps.

Date Acquired: October 6, 2008
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Scale: The large crater crosscut by the scarp is approximately 110 kilometers (70 miles) in diameter.

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington