MESSENGER Revealing Mercury’s Secrets

June 17, 2011 — Mercury is finally revealing its long-held secrets, thanks to a NASA spacecraft that has been orbiting the planet since March 18. NASA's MESSENGER, or MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, is giving scientists important clues about the planet’s origin and geological history, as well as helping them better understand its interior and exterior processes. "We are assembling a global overview of the nature and workings of Mercury for the first time," said MESSENGER principal investigator Sean Solomon of the Carnegie Institution for Science. "Many of our earlier ideas are being cast aside as new observations lead to new insights. Our primary mission has another three Mercury years to run, and we can expect more surprises as our solar system's innermost planet reveals its long-held secrets." The spacecraft has already provided tens of thousands of images showing detailed planetary features. The planet's surface previously had been seen only at comparatively low resolution but is now in sharper focus. The spacecraft has also collected extensive measurements of the chemical composition of Mercury's surface and topography and gathered global observations of the planet's magnetic field. Flyby images of Mercury had detected bright, patchy deposits on some crater floors. But new detailed images have revealed these patchy deposits to be clusters of rimless, irregular pits varying in size from several hundred feet to a few miles wide. These pits are often surrounded by diffuse halos of more reflective material and are found on central peaks, peak rings, and rims of craters. "The etched appearance of these landforms is unlike anything we've seen before on Mercury or the moon," said Brett Denevi, a staff scientist at the Johns Hopkins University Applied Physics Laboratory and a member of the MESSENGER imaging team. "We are still debating their origin, but they appear to be relatively young and may suggest a more abundant than expected volatile component in Mercury's crust." One of two instruments on the spacecraft designed to measure the quantity of key chemical elements on Mercury has made several important discoveries since the orbital mission began. Elemental ratios averaged over large areas of the planet's surface show that Mercury's surface differs markedly in composition from that of our Moon. Observations have revealed substantial amounts of sulfur at Mercury's surface, lending support to prior suggestions from ground-based telescopic observations that sulfide minerals are present. This discovery suggests that the original building blocks from which Mercury formed may have been less oxidized than those that formed the other terrestrial planets.

NASA’s MESSENGER spacecraft is giving scientists important clues to the origin of Mercury. Image credit: NASA This image, taken with the MDIS Narrow Angle Camera (NAC), shows two named craters imaged by both MESSENGER and Mariner 10. Date acquired: May 3, 2011. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington This image, taken with the Wide Angle Camera (WAC), shows a close-up of an unnamed crater. Date acquired: May 3, 2011. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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