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MESSENGER Approaches Two Billion Miles!
MESSENGER Approaches Two Billion Miles!
12 Sep 2007
(Source: Johns Hopkins University Applied Physics Laboratory)

On September 13, MESSENGER will reach the two billion-mile mark, placing the spacecraft about two-fifths of the way toward its destination to orbit Mercury. "This type of milestone is an impressive measure of how far we've traveled," says MESSENGER Principal Investigator Sean Solomon. "We can't take our craft into the shop for its two billion-mile check-up, but our experienced team is doing everything we can to ensure that at the end our journey our mission will be accomplished in full."

Mercury orbits deep within the well of the Sun's gravity. So, even though the closest planet to the Sun can be as close as 82 million kilometers (51 million miles) from Earth, getting the one-ton MESSENGER probe into orbit around Mercury is an extraordinarily difficult undertaking. The mission depends on the use of compact scientific instruments, lightweight materials, and an innovative trajectory using the gravity of Earth, Venus and Mercury itself to slow and shape the probe's descent into the inner solar system.

On its 4.9 billion-mile journey to becoming the first spacecraft to orbit the planet Mercury, MESSENGER has flown by Earth once and Venus twice to pick up gravity assists that are propelling it deeper into the inner solar system. Still to come are three flybys of Mercury.

Up next is an October 17 course correction event that will adjust MESSENGER's orbit in preparation for an encounter on January 14, 2008, that will bring it 200 kilometers (124 miles) above the surface of Mercury. Even though the MESSENGER spacecraft is three and a half years from reaching its final destination, the mission Science Team has been collecting data and sharing it with the larger scientific community. Those plans and results are available online at

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Last Updated: 12 Sep 2007