Artist's conception of NASA's Cassini spacecraft releasing the European Huygens probe toward Saturn's moon Titan. Photo: NASA

With its odometer marking some 2 billion kilometers (about 1.25 billion miles) of space travel, the Saturn-bound Cassini spacecraft has just entered the solar system's asteroid belt, the seldom-traversed ring of small rocky bodies that exists between Mars and Jupiter.

The Cassini flight team at NASA's Jet Propulsion Laboratory, Pasadena, Calif., reports that the spacecraft remains in excellent health and on track for its arrival at Saturn in July 2004. The mission is a joint effort of NASA, the European Space Agency and the Italian Space Agency. Telecommunications with the spacecraft are conducted through NASA's Deep Space Network of large, sensitive antennas located at stations in Spain, Australia and California.

Cassini, launched Oct. 15, 1997, passed by Earth in late August, using the pull of Earth's gravity to boost the spacecraft's speed and direct it toward the outer planets on its journey. Several of the spacecraft's science instruments recorded data during the Earth flyby, and preliminary results were presented by investigators last week at the American Geophysical Union's fall meeting in San Francisco.

The mission and science teams are busy preparing plans for Cassini's four-year orbital tour of Saturn. They are also working on additional opportunities to make observations and test out Cassini's science instruments during the spacecraft's flyby of Jupiter on Dec. 30, 2000, from a distance of approximately 10 million kilometers (6.2 million miles).

Cassini, carrying 12 scientific experiments, will enter orbit around the ringed planet in July 2004, and in November of that year, release the European Space Agency's Huygens probe to descend to the surface of Saturn's moon Titan.