The Cassini spacecraft between Saturn's rings and atmosphere
An artists rendering of the Cassini spacecraft between the rings of Saturn and the planet’s atmosphere. Courtesy JPL

Scientists at the Jet Propulsion Laboratory in Pasadena will send the Cassini spacecraft on the final phase of its 20-year mission Sunday when it begins a series of “ultra-close” passes through Saturn’s upper atmosphere, followed by a final plunge into the planet.

Cassini will make the first of five close flybys of Saturn at 9:22 p.m. Sunday, bringing the spacecraft to within 1,010 to 1,060 miles of the ringed planet’s cloud tops. The close orbit is expected to plunge the spacecraft into atmospheric conditions dense enough to require the use of rocket thrusters to keep the ship stable.

The conditions are expected to rival those experienced when Cassini made a series of close passes by the Saturn moon Titan.

“Cassini’s Titan flybys prepared us for these rapid passes through Saturn’s upper atmosphere,” said Earl Maize, Cassini project manager at JPL. “Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict.”

If Saturn’s atmosphere is too dense, mission managers may be forced to increase the altitude of the craft’s subsequent orbits. But if it is less dense, they may actually fly Cassini even closer to the planet on its final two passes, allowing it to collect close-up data on the atmospheric conditions.

“It’s long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we’re laying the groundwork for future exploration with this first foray,” said Linda Spilker, Cassini project scientist at JPL.

During the close flybys, Cassini is expected to take high-resolution images and collect data on Saturn’s auroras, temperature and vortexes at the planet’s poles.

The flybys will be a lead-in to Cassini’s dramatic finale, which will begin Sept. 11 with a pass by Titan that will bend the ship’s orbit. Cassini will plunge into the planet four days later.

The ship’s scientific instruments will be operating, but once it gets close to the planet, the atmospheric density will be so intense that Cassini’s rockets won’t be able to point the antenna toward Earth, cutting off communication. Moments later, the ship will break apart “like a meteor,” according to JPL.

Cassini was launched in 1997 and arrived at Saturn in 2004. It began the “Grand Finale” of its mission in late April with a close flyby of Titan, followed by a series of dives between the planet and its famous rings.

— City News Service

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Chris Jennewein

Chris Jennewein is Editor & Publisher of Times of San Diego.