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A Stellar Year in Space
Unmanned spacecraft probe new limits

As 2004 ends, NASA's Voyager 1 spacecraft is approaching the boundary of our solar system. After a 27-year, eight-billion-mile (thirteen-billion-kilometer) journey, it's reached the place where the outer wisps of the sun's atmosphere collide with interstellar gas. Now the spacecraft is poised to enter the great void between the stars, becoming humanity's first interstellar probe.
From the inner solar system to its outer limits, NASA's unmanned explorations this year rival science fiction. "There's been nothing like this in the 30 years I've been in the business," says Jay Bergstralh, NASA's senior scientist for space science research. In January two rovers landed on Mars, finding evidence the red planet once had water. June's arrival of the Cassini spacecraft at Saturn may lead to revelations about conditions in our solar system billions of years ago. And the tireless Hubble continues to churn out dazzling images.

In the decade between 1979 and 1989, Bergstralh says, NASA launched no interplanetary explorations. But since then new technologies and approaches have spawned a fleet of lightweight, lower-cost unmanned craft. NASA is even considering a plan to service Hubble with missions manned by humanoid "robonauts."
Trips to Mars now occur with amazing frequency. In the past decade, the United States, Europe, Russia, and Japan have launched ten missions to the red planet. But none matched the spectacular achievements of Mars rovers Opportunity and Spirit. Opportunity's landing in a crater with exposed layers of rock "was a bonanza moment," says Bergstralh. "The rock showed signs of wave action. That meant there were once standing bodies of water on the Mars surface. Liquid water means life is possible." Future missions, Bergstralh says, will dig deeper into rock to try to determine how long Mars had surface water and whether life ever evolved there.
In August a lightweight spacecraft named Messenger lifted off for Mercury, a planet visited once before in the mid-1970s, when the Mariner 10 probe made three flybys and imaged almost half the planet. Messenger will orbit the sunbaked planet in 2011, mapping its cratered surface. With no atmosphere, weather, or geologic processes churning up that surface, Mercury may still bear the imprint of what happened when the solar system was formed.
One disappointment this year occurred in September, when the parachutes that should have floated the spacecraft Genesis to a safe landing back on Earth failed to open. For nearly two years Genesis had hung in space a million miles (two million kilometers) away, capturing the solar wind—particles propelled from the sun at supersonic speed. Scientists are extracting atomic particles from the shattered debris. "We expect to find the original atomic recipe that went into the formation of the solar system," says Bergstralh.
One of the year's biggest thrills was the arrival of Cassini at Saturn after a seven-year flight. The spacecraft made a daring final approach through the outermost of Saturn's spectacular rings. Traveling at a top speed of nearly 70,000 mph (110,000 kph),  Cassini passed just 12,000 miles (19,000 kilometers) above Saturn's cloud tops as its engine fired, slowing it into orbit. "It was white-knuckle time," says Robert Mitchell, Cassini's project manager. Though the flight path through the rings had been carefully surveyed, even a pebble could have crippled the high-speed spacecraft, Mitchell says.
It will no doubt be white-knuckle time again on December 25, when Cassini—a joint effort by the European and Italian Space Agencies and NASA—launches Huygens to probe Saturn's moon Titan. Resembling a much younger and far colder Earth, Titan has large regions that may be oceans of liquid hydrocarbons such as methane and ethane. What Huygens finds on Titan could open a new chapter in understanding how our solar system—and life—originated.

—Bill Douthitt

Web Links

NASA Space Sciences Missions
To learn more about all the missions mentioned in this article as well as other past and future missions visit this site. On each mission page you will find information on the mission, science objectives, spacecraft specifics, and images, as well as special links for kids and educators.

This website is a great starting place to learn more about NASA.


Leverington, David. Babylon to Voyager and Beyond: A History of Planetary Astronomy.  Cambridge University Press, 2003.
Verger, Fernand, and others.  The Cambridge Encyclopedia of Space: Missions, Applications and Explorations. Trans. Stephen Lyle and Paul Reilly. Cambridge University Press, 2003.


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