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MESSENGER Mission News
August 17, 2010

Vulcanoid Search Continues as MESSENGER Reaches Orbital Perihelion
Today MESSENGER will pass within 0.308 astronomical units (AU) of the Sun (one AU is Earth’s distance from the Sun, approximately 150 million kilometers or 93 million miles), providing MESSENGER scientists with another opportunity to search for vulcanoids. Named after the hypothetical planet Vulcan, whose existence was disproven in 1915, vulcanoids are asteroids that orbit the Sun inside the orbit of the planet Mercury.

No vulcanoids have yet been discovered, and it is not known if any exist. But should they be found, these small, rocky asteroids may yield insights into the formation and early evolution of the solar system. They might contain material left over from the earliest period of planet formation and help determine the conditions under which the terrestrial planets, particularly Mercury, formed. Vulcanoids would also represent an additional population of impactors that contributed to the cratering history of Mercury much more than that of any other body. Impacts by vulcanoids would make the planet's surface appear older, relative to the surfaces of the Moon and other inner planets, than it actually is.

If they do exist, the vulcanoids would be difficult to spot. First, they would be very small – less than 60 kilometers (37 miles) in diameter (a limit set by Earth-based observations) – and their reflected light would generally be drowned out by the bright glare of the nearby Sun. Because of their proximity to the Sun, searches for vulcanoids from the ground can be carried out only during twilight or or dawn or during solar eclipses.

The mission's imaging team is taking advantage of the probe's proximity to the region of space inside Mercury’s orbit during this perihelion to continue their search for vulcanoids. The latest search started on August 14 and continues through today.

“Our searches for vulcanoids may not turn up any objects,” says MESSENGER principal investigator Sean Solomon, of the Carnegie Institution of Washington, “but a discovery of even one vulcanoid would change our thinking about the evolution of Mercury. The solar system still has many surprises in store for us, so it makes sense for us to be ready for the unexpected.”

Earth and Moon from 114 Million Miles

This image was acquired on May 6, 2010, as part of MESSENGER's campaign to search for vulcanoids. In the lower left portion, the Earth can be seen, as well as the much smaller Moon to Earth’s right. When MESSENGER took this image, a distance of 183 million kilometers (114 million miles) separated the spacecraft and Earth. To provide context for this distance, the average separation between the Earth and the Sun is about 150 million kilometers (93 million miles).

Engineer Helps MESSENGER Maintain Balance Between Staying Cool and Staying Powered

Kim Ord worked on the International Space Station at the NASA Johnson Space Center in Houston, Texas, for ten years. When Houston’s heat became unbearable, she moved to Maryland to work on MESSENGER at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel. Ord is the power and thermal mission operations analyst for MESSENGER’s mission operations team. To learn more about how she helps MESSENGER preserve the delicate balance between maintaining safe temperatures and generating sufficient power, read her profile here: http://messenger.jhuapl.edu/who_we_are/member_focus.html.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

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