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NASA Sets Mercury Mission Launch for Aug. 2

Posted on: Monday, 26 July 2004, 06:00 CDT

Jul. 26--NASA and a team from Johns Hopkins University are preparing to launch a $426 million mission to Mercury -- the ugly little planet where it is hotter than a pizza oven.

Messenger is to lift off atop a Boeing Delta 2 rocket from Cape Canaveral Air Force Station, Fla., in the predawn of Aug. 2. The launch will kick off a seven-year journey to Mercury.

Scientist hope the spacecraft will help them understand subtle differences among the terrestrial planets -- the rocky worlds that orbit closest to the sun.

"Understanding Mercury, how it formed and evolved, is essential to the understanding of the terrestrial planets, Venus, Earth and Mars and of course understanding their unique histories," said Orlando Figueroa, director of NASA's solar system exploration division.

Of all the solar system's planets, only distant Pluto has received less scrutiny than Mercury, which is slightly larger than the Earth's moon. And now, many astronomers believe Pluto is more rock and icy waste left over from the solar system's assembly processes than a bona fide planet.

Launched in 1973, NASA's Mariner 10 was the first and so far the only spacecraft to visit Mercury.

Mariner was capable only of three brief photo passes in the two years that followed.

The imagery captured a little less than half of the planet, revealing a scalding terrain pummeled by impacts from meteorites.

"Mariner 10 left us with more questions than it answered," said Sean Solomon, of the Carnegie Institution in Washington, who serves as the Messenger mission's chief investigator.

"Now, 30 years later, advances in technology, flight design and materials are enabling us to go back with a more capable mission."

Messenger is equipped to orbit Mercury for at least a year, long enough to examine all of the terrain with its cameras and other instruments.

Mariner's discoveries and those from pinging Mercury with powerful radar signals from Earth reveal the possibility that large craters at the south and north poles may hold deposits of ice left from collisions with comets.

Even with surface temperatures that reach 840 degrees Fahrenheit, conditions deep in those craters may be freezerlike.

Messenger will peer into the recesses to confirm the presence of ice, or identify other deposits of sulphur or silicate minerals.

Another of Mercury's mysteries is its high abundance of iron, the dense metal that forms the Earth's core and contributes to the presence of a strong magnetic field.

With the instruments carried by Messenger, scientists expect to examine several explanations for the abundance of iron.

--Theorists believe a vast dust and gas disk that surrounded a young sun condensed into planets 4.6 billion years ago. Perhaps the disk was iron-rich closest to the sun.

--Maybe Mercury was more like Earth in its early era. Powerful impacts from large meteorites smacked the planet's outer layers away. Or the sun's heatmay have baked the layering away.

"Of the questions we are going after, the most fundamental is how Mercury is put together," Solomon said.

Messenger's unusual trajectory will swing it by Earth next year and close to Venus twice. Each pass will increase the probe's velocity enough to reach Mercury with just the right momentum to maneuver into orbit in March 2011.

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