Nov 3 2009
From The Space Library
NASA announced that its MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft had performed its third and final Mercury flyby on 29 September, giving scientists a nearly complete view of the planet’s surface for the first time. While completing a critical gravity-assist maneuver, which would keep the spacecraft on course for entering into orbit around Mercury in 2011, MESSENGER’s cameras and instruments collected high-resolution and color images. These images unveiled an additional 6 percent of the planet’s surface that NASA had never imaged at close range, bringing the total amount of Mercury’s surface imaged by NASA spacecraft to 98 percent. The flyby revealed new features of Mercury, including a region with a bright sea, surrounding an irregular depression that scientists suspected was volcanic in origin. The flyby also revealed a double-ring impact basin approximately 180 miles (290 kilometers) across, similar to the so-called Raditladi basin, which scientists had first viewed during MESSENGER’s initial flyby in January 2008. Another instrument on board the craft carried out the most extensive observations to date of Mercury’s exosphere. The flyby enabled MESSENGER to carry out the first detailed scans over Mercury’s north and south poles and to capture data that would begin to reveal how Mercury’s atmosphere varies with its distance from the Sun. Ronald J. Vervack, a participating scientist affiliated with the Johns Hopkins University Applied Physics Laboratory, remarked on the presence of seasonal effects in Mercury’s exosphere, stating that the planet’s exosphere was one of the most dynamic in the solar system. Scientists intended to study the seasonal changes in all exospheric constituents, including sodium, calcium, and magnesium, to understand the processes that generate, sustain, and modify Mercury’s atmosphere. Finally, the flyby revealed that Mercury’s surface contains more iron and titanium than previously thought. This finding reversed scientists’ earlier idea that, despite Mercury’s iron-titanium core, its surface is composed almost entirely of silicate-based materials.
NASA, “MESSENGER Spacecraft Reveals More Hidden Territory on Mercury,” news release 09-257, 3 November 2009, http://www.nasa.gov/home/hqnews/2009/nov/HQ_09-257_Messenger.html (accessed 18 November 2011); Peter N. Spotts, “NASA’s Messenger Probe Reveals New Clues About Mercury,” Christian Science Monitor, 4 November 2009.
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