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July 30, 2012
This striking image shows the progression of daylight across the surface of Mercury. This line separating night from day is called the terminator. Scientists have studied interesting phenomena occurring near the terminator of the Moon for years. Such occurrences involve the interaction between lunar dust and charged solar particles. Because Mercury's regolith is exposed to almost ten times as many charged particles as the Moon, it is an excellent place to study the effects of solar radiation on surface materials. In this unprojected image, north is to the right. This image was acquired as part of MDIS's campaign to monitor the south polar region of Mercury. By imaging the polar region approximately every four MESSENGER orbits as illumination conditions change, features that were in shadow on earlier orbits can be discerned and any permanently shadowed areas can be identified after repeated imaging over one solar day. During MESSENGER's one-year primary mission, MDIS's WAC was used to monitor the south polar region for the first Mercury solar day (176 Earth days), and MDIS's NAC made repeated images of the south polar region during the second Mercury solar day. The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury? section of this website to learn more about the key science questions that the MESSENGER mission is addressing. During the one-year primary mission, MESSENGER acquired 88,746 images and extensive other data sets. MESSENGER is now in a yearlong extended mission, during which plans call for the acquisition of more than 80,000 additional images to support MESSENGER's science goals. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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