After a seven-year, 3.5-billion-km journey, NASA’s Cassini spacecraft fired its engine for 96 minutes on July 1, changed course-and became the first man-made object in orbit around Saturn. Over the next four years, the spacecraft will circle the planet 76 times, sending back data about its composition, its rings and its satellites, including the giant moon Titan, where Cassini will drop a probe in January. Deputy project scientist Linda Spilker was at the Jet Propulsion Laboratory in Pasadena, Calif., along with many of the 250 scientists involved, at the historic moment. She describes their reaction-and why the mission matters.
It was a euphoric feeling. I could feel the excitement building, knowing that we’d
made it into orbit and that we’d be getting our highest resolution images ever of the rings. There was lots of hugging and shouts of hurray and high-fiving.
The spacecraft was going in very close to the planet. We pointed the high-gain antenna in the direction of any incoming particles, and we knew that small dust-sized particles would hit the antenna and vaporize. It was the bigger, marble-sized particles we were worried about-they could do substantial damage.
We have 45 flybys of Titan, and then seven of Saturn’s other icy moons. With Enceladus
we may get as close as 100 or 200 km. The part that will be very exciting is the end of the tour, where the spacecraft’s orbit will be almost over the poles of Saturn, which means the rings will be opened right up and we’ll get some good close views.
Saturn’s rings appear to be quite young relative to the age of the solar systemmaybe only a few hundred million years old. So you have to ask, how did the ring system form? It could have been an object that was going through the system and got too close and was just torn apart, and then those particles ended up circling the planet. We think the planets formed from a disk of gas and dust around the sun, so if you can understand Saturn you can get some clues as to how our solar system may have formed. □
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