January 31, 2008—A color image taken by the MESENGER spacecraft shows the side of Mercury previously unseen by human eyes.

The shot, released yesterday, is a mosaic of images from the craft's 11 narrow-band color filters.

Subtle patterns revealed by the filters—which can capture light in wavelengths invisible to the naked eye—will help astronomers determine the mineral composition of the planet's surface.

The bright spots with a bluish tinge are relatively recent impact craters. Some of these have bright streaks, called “rays.” The streaks are made from crushed rock that was blasted outward during an impact.

The large, light-colored circle in the upper right of the image is the inside of the Caloris Basin. The only previous mission to Mercury, Mariner 10, viewed only the eastern (right) portion of this enormous impact crater.

MESSENGER has now shown that Caloris is filled with smooth plains that are brighter than the surrounding terrain—the opposite of the shading differences on Earth's moon.

—Anne Minard

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