Exploring the Evolution of the Caloris Basin
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Exploring the Evolution of the Caloris Basin

August 18, 2008

The Caloris basin on Mercury is one of the youngest large impact basins in the Solar System, and MESSENGER images are enabling scientists to study it in ways not previously possible. This image, acquired by the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS), was taken on January 14, 2008, and shows an area that is about 280 kilometers across (about 170 miles) on the floor of the basin. Bright rays from a young impact crater extend into the image from the top right corner. This bright-rayed crater is located slightly left of the center of the basin and is easily spotted on the previously released image that shows the entire Caloris basin.

The spectacular fractures seen cutting the floor of the basin, as visible in this image, show that extensional (pull-apart) forces deformed Mercury's crust in the ancient past. Impact craters can be observed on top of the fractures and the fractures do not deform the craters, indicating that the fractures are ancient. The fractures are observed in the smooth plains material that fills the Caloris basin, are found near the outer edges of the basin, and are oriented roughly concentric with the basin's rim. This orientation is in contrast to a series of radial fractures located in the center of the Caloris basin. The fractures were likely formed when the floor of the basin was uplifted, causing horizontal stretching and breaking apart of the material that filled the basin. Similar concentric fractures were observed on the eastern side of the basin that was photographed by Mariner 10. By mapping out the extent of these fractures and other tectonic features, MESSENGER scientists are exploring how Mercury's great Caloris basin evolved after it formed.

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