Planetary experts say they're "jazzed up" for a potential scientific bonanza today as a spacecraft from Earth flies within 125 miles of the planet Mercury.
The Maryland-built Messenger spacecraft, launched by NASA in 2004, will buzz the planet nearest the sun about 2 p.m. today, providing mankind's first close-up look in 33 years.
Today's visit is only a prologue. In 2011, Messenger is to begin a year in orbit around Mercury. But researchers say they hope the craft will start today to answer some of the vexing questions that arose after Mariner 10 flew past the bizarre little world in 1974 and 1975.
One puzzler: Just how did tiny Mercury, with its big, dense metal core and strong magnetic field, evolve just 30 million miles from the sun? Some theorists say they believe the planet might have formed much farther from the sun and migrated later to its present orbit.
"I think we're in for some big surprises," said Faith Vilas, a scientist with the mission and director of the MMT Observatory at Mount Hopkins, Ariz. She has been studying Mercury since the days before Mariner 10 photographed 45 percent of its surface.
"The first thing most of us want to see is what the other 55 percent of Mercury's surface looks like," she said.
Marilyn Lindstrom, Messenger program scientist at NASA headquarters, said it was like waiting 30 years to decide a Super Bowl matchup.
"We've been waiting to go back to Mercury that long, and people are that jazzed up," she said. "Not just the science team, but the entire planetary science community."
Eight years in development, the $446 million Messenger mission was designed and is managed by the Johns Hopkins University's Applied Physics Lab near Laurel. Engineers control the craft from an operations center on the APL campus.
After a 3 1/2 -year, 4.9 billion-mile journey, Messenger will zip past Mercury today at a relative speed of 16,000 mph, passing within 124 miles of the planet's surface at 2:04 p.m.
During 55 hours of flyby operations, the spacecraft is taking 1,300 pre-programmed photos and spectroscopic observations. Its seven instruments will map Mercury's surface chemistry and mineralogy, its magnetic field and tenuous atmosphere - all clues to its evolution, structure and natural environment.
Mercury is currently in the Earth's daytime sky, just east of the sun. After sunset, it is faintly visible low in the western sky, setting about 5:30 p.m. Messenger is passing from west to east behind the planet as seen from Earth.
