Flyby details mercury's unobserved terrain.

Flying within 228 kilometers of Mercury's surface on September 29, the MESSENGER spacecraft snapped portraits of a portion of the planet that had never before been imaged close up. The encounter was the mission's third and last flyby and gave the craft the gravitational assistance it needs to settle in March 2011 into a year-long orbit around Mercury, the solar system's innermost and least explored planet. Images from the latest encounter (one shown here) detailed 5 percent of the planet that had never been examined by spacecraft before.

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