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Far more NASA probes

Posted on: Sunday, 21 March 2004, 06:00 CST

Far more NASA probes

Itinerary includes Mercury, Venus, Jupiter and Saturn

By ROBERT S. BOYD Knight Ridder News Service

Sunday, March 21, 2004

Washington -- Mars is getting all the attention right now, but five other members of the solar system will be getting close-up examinations this year. Mercury, Venus, Jupiter, Saturn and Titan, Saturn's planet-sized moon, are slated for visits by spaceships bristling with scientific instruments.

Astronomers say these missions through the solar system could shed new light on the origin, development and fate of our planet.

"We use these planets as laboratories for understanding how things work here on Earth," said Torrence Johnson, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"We need to understand the overall system, not just Mars," said Carle Peters, a solar system expert at Brown University in Providence, R.I. "The story is different for each body in the solar system."

For example, scientists still don't know how life began on Earth or where the water in our oceans came from.

"By looking at worlds with different environments, we can get a better idea of how these processes work on Earth," said Ralph Lorenz, a researcher at the University of Arizona in Tucson.

Exploring the solar system with unmanned spaceships is much cheaper than sending humans to the moon and Mars, as President Bush has proposed. NASA's budget for these robotic missions is $629 million for the next fiscal year, compared with $6.7 billion for manned spaceflight involving shuttles and the International Space Station. The eventual cost of putting people on the moon and Mars, starting in the next decade, is likely to be a hundred billion dollars or more.

Mercury, Venus mission

Coming up in May is a mission to Mercury and Venus scheduled for launch from Florida's Cape Canaveral. A spacecraft named Messenger will loop three times around Venus, gathering data as it goes. Afterward, it will pass Mercury twice before settling into a yearlong orbit around the broiling little planet closest to the sun in July 2009. Its total cost will be $358 million.

Although 20 missions have visited, orbited and landed on Venus, only one other spaceship has flown by Mercury. NASA's Mariner 10 made three flybys 30 years ago, but it was able to take pictures of only half the planet. Messenger's assignment is to produce a color map of Mercury's entire surface.

Mercury is one of the most peculiar objects in the solar system. Barely a third the size of Earth, it's basically a big lump of iron, covered by a layer of rock. Huge craters and mile-high cliffs stretching as far as 100 miles mark the surface.

To screen itself from the sun's searing heat, Messenger will carry a sunshade shaped like half a parasol. Temperatures on Mercury's day side reach 870 degrees Fahrenheit, then plunge to minus 350 degrees at night. Ice may exist in dark craters at the north and south poles.

Cassini headed for Saturn

Meanwhile, Cassini, an American-European spaceship, will enter orbit around Saturn on July 1, completing a seven-year voyage past the inner planets. Cassini will spend four years studying Saturn, its spectacular rings and some of its 31 moons.

On its first orbit, Cassini will pass over Titan, Saturn's biggest moon. Titan is "the largest single piece of unexplored real estate in the solar system," said Lorenz.

This December, Cassini will eject a scientific lander -- not a mobile rover as on Mars -- called Huygens, after the Dutch astronomer Christiaan Huygens, who discovered Titan in 1655.

Huygens will coast for 22 days down through Titan's hazy atmosphere to make a parachute landing on its surface. During its descent and perhaps for 30 minutes after landing, the probe will relay data via Cassini to eager scientists on Earth.

Astronomers are fascinated by Titan because its thick atmosphere, composed mostly of nitrogen and methane, may resemble what existed on Earth when life began nearly 4 billion years ago.

Scientists don't believe any known form of life, even microorganisms, can exist on the hostile surface of the moon. "We don't expect to find a living Titan," Lorenz said. But the mission "may help us understand the first steps toward life."

Meanwhile, Ulysses, a spaceship that has been studying the sun since 1994, is swinging around Jupiter this month to gain new energy for its return to the sun and to gather data about the giant planet.

Mercury-Messenger: messenger.jhuapl.edu Cassini-Huygens: saturn.jpl.nasa.gov

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