This graphic shows the closest approaches of Cassini’s final two orbital phases. Ring-grazing orbits are shown in gray (at left); Grand Finale orbits are shown in blue. The orange line shows the spacecraft’s Sept. 2017 final plunge into Saturn. Image credit: NASA/JPL-Caltech
NASA’s Saturn-orbiting Cassini spacecraft has made its first close dive past the outer edges of Saturn’s rings since beginning its penultimate mission phase on Nov. 30. Cassini crossed through the plane of Saturn’s rings on Dec. 4 at 5:09 a.m. PST at a distance of ~57,000 miles above Saturn’s cloud tops. This is the approximate location of a faint, dusty ring produced by the planet’s small moons Janus and Epimetheus, and just 6,800 miles from the center of Saturn’s F ring.
About an hour prior to the ring-plane crossing, the spacecraft performed a short burn of its main engine that lasted about 6 seconds. About 30 minutes later, as it approached the ring plane, Cassini closed its canopy-like engine cover as a protective measure. “With this small adjustment to the spacecraft’s trajectory, we’re in excellent shape to make the most of this new phase of the mission,” said Earl Maize, Cassini project manager at NASA’s JPL, CA. A few hours after the ring-plane crossing, Cassini began a complete scan across the rings with its radio science experiment to study their structure in great detail.
Cassini’s imaging cameras obtained views of Saturn about 2 days before crossing through the ring plane, but not near the time of closest approach. The focus of this first close pass was the engine maneuver and observations by Cassini’s other science instruments. Future dives past the rings will feature some of the mission’s best views of the outer regions of the rings and small, nearby moons. Each of Cassini’s orbits for the remainder of the mission will last 1 week. The next pass by the rings’ outer edges is planned for Dec. 11. The ring-grazing orbit, 20 in all, will continue until April 22, when the last close flyby of Saturn’s moon Titan will reshape Cassini’s flight path. With that encounter, Cassini will leap over the rings, making the first of 22 plunges through the 1,500-mile-wide gap between Saturn and its innermost ring on April 26.
On Sept. 15, the mission will conclude with a final plunge into Saturn’s atmosphere. During the plunge, Cassini will transmit data on the atmosphere’s composition until its signal is lost. 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 with indications of hydrothermal activity within the moon Enceladus, and liquid methane seas on another moon, Titan.
http://www.jpl.nasa.gov/news/news.php?feature=6690
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