On January 14, 2008, MESSENGER's Mercury Laser Altimeter (MLA) became the first instrument to measure the distance between a spacecraft and the surface of Mercury. MLA operates by first firing a brief laser pulse at the surface. It then measures the time for the pulse to reach the surface and return to the spacecraft, thereby providing a precise distance.

This figure shows the distance, or range, from the MESSENGER spacecraft to the surface of Mercury as measured by MLA during the flyby of Mercury. The instrument acquired the surface at a slant range of about 600 kilometers (about 370 miles) and tracked the surface through closest approach near 200 kilometers (about 125 miles) and out to a distance of about 1500 kilometers (about 930 miles). During the Mercury encounter, the instrument met or exceeded all performance specifications. The MESSENGER team is continuing to process the MLA data, and the final results should enable distances to be measured to better than a meter, allowing the profiles of craters and other features to be measured.

The vertical exaggeration in the figure is about 5:1. The MLA was designed and built at the NASA Goddard Space Flight Center.

Credit: NASA/Goddard Space Flight Center/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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