NASA said its Cassini mission is set to begin on November 30 a daring set of “ring-grazing” orbits, during which it will fly closer to Saturns rings than it has since its 2004 arrival. On November 30, following a gravitational nudge from Saturn’s moon Titan, Cassini will enter the first phase of the mission’s dramatic endgame, NASA said.
“We’re calling this phase of the mission Cassini’s Ring-Grazing Orbits, because we’ll be skimming past the outer edge of the rings,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.
“In addition, we have two instruments that can sample particles and gases as we cross the ringplane, so in a sense Cassini is also ‘grazing’ on the rings,” Spilker said.
Launched in 1997, Cassini has been touring the Saturn system since arriving there in 2004 for an up-close study of the planet, its rings and moons. During its journey, Cassini has made numerous dramatic discoveries, including a global ocean within Enceladus and liquid methane seas on Titan.
Between November 30 and April 22, Cassini will circle high over and under the poles of Saturn, diving every seven days — a total of 20 times — through the unexplored region at the outer edge of the main rings. On many of these passes, Cassini’s instruments will attempt to directly sample ring particles and molecules of faint gases that are found close to the rings.
During the first two orbits, the spacecraft will pass directly through an extremely faint ring produced by tiny meteors striking the two small moons Janus and Epimetheus. Ring crossings in March and April will send the spacecraft through the dusty outer reaches of the F ring. The F ring marks the outer boundary of the main ring system. Saturn has several other, much fainter rings that lie farther from the planet.
During these orbits, Cassini will pass as close as about 90,000 kilometres above Saturn’s cloud tops. But even with all their exciting science, these orbits are merely a prelude to the planet-grazing passes that lie ahead.
In April 2017, the spacecraft will begin its “Grand Finale” phase. After nearly 20 years in space, the mission is drawing near its end because the spacecraft is running low on fuel, NASA said.
During its grand finale, Cassini will pass as close as 1,628 kilometres above the clouds as it dives repeatedly through the narrow gap between Saturn and its rings, before making its mission-ending plunge into the planet’s atmosphere on September 15, 2017.
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