Hot as a pizza oven on one side and colder than an Antarctic winter on the other, the planet Mercury isn't a place most people would spend good money to visit.
But scientists and engineers in Maryland and across the country are as happy as tourists queued for a flight to the tropics as they await the planned Aug. 2 launch of the first mission in 31 years to the sun's nearest neighbor.
Called Messenger, the unmanned, desk-sized spacecraft was designed and built at the Johns Hopkins University's Applied Physics Laboratory near Laurel. Its scientific instruments were built at NASA's Goddard Space Flight Center in Greenbelt, the University of Colorado and the University of Michigan.
Messenger's 7 1/2 -year mission: to go where only NASA's Mariner 10 has gone before, to answer questions that have lingered since Mariner's flybys in 1973 and 1974.
"Messenger will help us understand the forces that have shaped the least-explored and innermost of the terrestrial planets," said Orlando Figueroa, NASA's director of solar system exploration. "Mariner left us with even more questions than answers."
The most fundamental is "how Mercury got put together," said the Carnegie Institution's Sean C. Solomon, principal investigator on the Mariner team.
"The [four] inner planets are litter-mates, if you will, products of a single early stage in the evolution of a star and its planetary system," he said. "And yet the siblings turned out very different."
Composed mostly of metal rather than lighter rocks, Mercury is denser than Venus, Earth and Mars. It's also the only one of the four with no significant atmosphere, and one of two with a magnetic field. (Earth is the other.)
"In order to understand what processes most control the differences in outcome, we really have to study and learn about the most extreme of these outcomes," Solomon said.
$426 million mission
The $426 million Messenger mission is set to begin shortly after 2 a.m. Aug. 2 with liftoff atop a Delta 2 rocket from the Cape Canaveral Air Force Station in Florida. If there are delays, the launch window reopens each night until Aug. 14.
If all goes well, the 1.2-ton craft will make 15 loops around the sun. It will swing by Earth again in August 2005, past Venus twice (October 2006 and June 2007) and by Mercury three times in 2008 and 2009.
In March 2011, after a circuitous journey of 4.9 billion miles, it will slip into a nearly polar orbit of Mercury, swooping as low as 125 miles from the surface.
