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by Staff Writers Laurel MD (SPX) Jun 17, 2011
After nearly three months in orbit about Mercury, MESSENGER's payload is providing a wealth of new information about the planet closest to the Sun, as well as a few surprises. The spacecraft entered orbit around Mercury on March 18, 2011 UTC, becoming the first spacecraft ever to do so. Tens of thousands of images of major features on the planet - previously seen only at comparatively low resolution - are now available in sharp focus. Measurements of the chemical composition of Mercury's surface are providing important clues to the origin of the planet and its geological history. Maps of the planet's topography and magnetic field are revealing new clues to Mercury's interior dynamical processes. And scientists now know that bursts of energetic particles in Mercury's magnetosphere are a continuing product of the interaction of Mercury's magnetic field with the solar wind. This week, MESSENGER completed is first perihelion passage from orbit, its first superior solar conjunction from orbit, and its first orbit-correction maneuver. "Those milestones provide important context to the continuing feast of new observations that MESSENGER has been sending home on nearly a daily basis," offers MESSENGER Principal investigator Sean Solomon of the Carnegie Institution of Washington.
A Surface Revealed in Unprecedented Detail New targeted Mercury Dual Imaging System images at up to 10 meters per pixel reveal these patchy deposits to be clusters of rimless, irregular pits varying in size from hundreds of meters to several kilometers. These pits are often surrounded by diffuse halos of higher-reflectance material, and they are found associated with 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," says Brett Denevi, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and a member of the MESSENGER imaging team. "We are still debating their origin, but they appear to have a relatively young age and may suggest a more abundant than expected volatile component in Mercury's crust."
Mercury's Surface Composition XRS observations have also revealed substantial amounts of sulfur at Mercury's surface, lending support to prior suggestions from ground-based telescopic spectral observations that sulfide minerals are present. This discovery suggests that the original building blocks from which Mercury was assembled may have been less oxidized than those that formed the other terrestrial planets, and it has potentially important implications for understanding the nature of volcanism on Mercury.
Mapping of Mercury's Topography and Magnetic Field Two decades ago, Earth-based radar images showed that around both Mercury's north and south poles are deposits characterized by high radar backscatter. These polar deposits are thought to consist of water ice and perhaps other ices preserved on the cold, permanently shadowed floors of high-latitude impact craters. MESSENGER's altimeter is testing this idea by measuring the floor depths of craters near Mercury's north pole. To date, the depths of craters hosting polar deposits are consistent with the idea that those deposits occupy areas in permanent shadow.
Energetic Particle Events at Mercury "We are assembling a global overview of the nature and workings of Mercury for the first time," adds Solomon, "and 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."
Related Links Johns Hopkins University Applied Physics Laboratory (APL) News Flash at Mercury Mars News and Information at MarsDaily.com Lunar Dreams and more
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