Date: Friday, 30-September-2016, 1:08 AM | Message # 1
Since NASA’s Cassini spacecraft arrived at Saturn, the planet’s appearance has changed greatly. This view shows Saturn’s northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017.
After over 12 years at Saturn, studying the planet and its rings and moons, NASA’s Cassini spacecraft has entered the final year of its mission. Before the spacecraft’s long journey ends in September 2017, Cassini will complete a daring two-part endgame that will take it close to Saturn’s F ring, and finally into the gap between the rings and Saturn itself.
Starting on November 30, Cassini’s orbit will send it just past the edge of Saturn’s main rings. The spacecraft will perform a series of 20 of these orbits, called F-ring orbits. Cassini will approach to within 4,850 miles (7,800 kilometers) of the center of the narrow F ring, with its odd kinked and braided structure.
“During the F-ring orbits we expect to see the rings, along with the small moons and other structures embedded in them, as never before,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “The last time we got this close to the rings was during arrival at Saturn in 2004, and we saw only their backlit side. Now we have dozens of opportunities to examine their structure at extremely high resolution on both sides.”
The final phase of Cassini’s mission, called the Grand Finale, will begin in April 2017. A close approach of Saturn’s giant moon Titan will alter the spacecraft’s orbit so that it passes through the gap between Saturn and its rings, an unexplored space about 1,500 miles (2,400 kilometers) wide. Cassini is expected to make 22 plunges through this gap, starting with its first dive on April 27.
During the Grand Finale, Cassini will make its closest-ever observations of Saturn, mapping the planet’s magnetic and gravity fields, and capturing ultra-close views of the atmosphere. Researchers hope to gain insights into Saturn’s internal structure, the exact length of a Saturnian day, and the total mass of the rings, which may help determine their age. Cassini will also directly analyze dust-sized particles in the main rings and sample the outermost regions of Saturn’s atmosphere.
“It’s like getting a whole new mission,” said Spilker. “The scientific value of the F ring and Grand Finale orbits is so compelling that you could imagine a whole mission to Saturn designed around what we’re about to do.”
Since the beginning of this year, mission engineers have been adjusting Cassini’s orbit around Saturn to ready the spacecraft for the final phase of its mission. They have sent the spacecraft on a series of flybys of Titan that are gradually raising the tilt of Cassini’s orbit in respect Saturn’s equator and rings. This will enable the spacecraft to leap over the rings with a final flyby of Titan in April 2017, to begin the Grand Finale.
The Grand Finale will come to a dramatic conclusion on September 15, 2017. Cassini will dive into Saturn’s atmosphere, transmitting data about the planet’s chemical composition until the signal is lost. Friction with the atmosphere will cause the spacecraft to burn up like a meteor a short time afterward.