September 26, 2017

Cassini survives closest brush with Saturn’s inner ring

This unprocessed image from Cassini’s camera taken Sunday shows Saturn (upper right) and a portion of the planet’s rings refracted through Saturn’s atmosphere. Credit: NASA/JPL-Caltech/Space Science Institute

Barreling through space near the inner edge of Saturn’s wispy D ring, NASA’s Cassini spacecraft shielded itself from bits of ice and dust Sunday as the probe made its most dangerous plunge close to the planet, collecting spectacular edge-on views of Saturn’s rings with an on-board camera.

The raw images returned during Sunday’s encounter show new close-up angles of the structure of Saturn’s rings, and Cassini also turned its radar instrument to scan the rings in a first-of-its-kind experiment.

Cassini’s closest approach to Saturn occurred at 1422 GMT (10:22 a.m. EDT) Sunday, but the spacecraft was out of radio contact with Earth at the time. Engineers uplinked commands for Cassini to turn its high-gain communications antenna to point in its direction of travel, protecting the probe from any incoming microscopic ice particles.

Officials confirmed a few hours later that Cassini re-established contact with controllers at NASA’s Jet Propulsion Laboratory in California. Images from the flyby began arriving on Earth on Monday.

Cassini captured this image of Saturn’s rings Sunday. The unprocessed image has been rotated to view on this page. Credit: NASA/JPL-Caltech/Space Science Institute

Sunday’s flyby was the closest Cassini will come to Saturn’s D ring, the innermost of the planet’s rings. It was the sixth time Cassini has sailed through the gap between Saturn and its rings after the spacecraft reshaped its orbit in April with the mission’s final close-range flyby the Saturn’s largest moon Titan.

Running low on fuel, the plutonium-powered spacecraft is in its final months, with its orbit around Saturn now taking it on weekly plunges through the ring gap. Cassini will fall into Saturn’s atmosphere and be crushed Sept. 15.

Cautious managers directed the antenna to point forward — in its so-called “ram” position — during Cassini’s first flight through the ring gap last month. But scientists detected fewer impacts from ice particles than predicted, allowing later flybys to forego the safeguard.

Artist’s concept of the Cassini spacecraft at Saturn. Credit: NASA/JPL-Caltech

The passage Sunday, along with three more in June and July, will place Cassini much closer to the D ring, and controllers will again turn the craft’s antenna into a shield for those encounters. Cassini’s next visit to the ring gap on June 3, U.S. time, will be its second-closest brush with the D ring, again requiring the use of the antenna for protection.

Scientists say Cassini’s “grand finale” will help them learn about Saturn’s atmosphere, interior and magnetic field. Another prime objective of the flybys is to measure the mass and estimate the age of Saturn’s rings, which will tell scientists about their origin.

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