Last days: Saturn will keep its remaining secrets after Cassini’s death plunge NASA/JPL-Caltech/SSI

In a few days, we will receive our last signal from the Cassini spacecraft. But for a few of hours before that, the spacecraft will live-stream a deluge of data to Earth in its last hurrah before burning up in Saturn’s atmosphere.

Over the past month, Cassini has been dipping into the very top of the Saturn’s atmosphere on its last few passes by the planet. It has measured the particles, radiation and magnetic field there. Now, it’s diving right in and capturing data deeper in Saturn’s atmosphere than any spacecraft has ever ventured.

Cassini’s grand finale: Join us as we count down to the fiery end of the Cassini spacecraft’s mission to Saturn

“We’ll be about 2000 kilometres lower than we’ve ever been, and then the atmosphere will eventually swamp us and overcome us and the spacecraft will melt,” says Julie Webster, Cassini’s manager of spacecraft operations at NASA’s Jet Propulsion Laboratory.

Typically, Cassini stores data from its instruments on a hard drive for at least a few hours before transmitting it back to Earth. But since the spacecraft will only survive a few minutes after it begins its final fiery plunge, it will stream the data from its last few hours in real time.

Mission improbable



There won’t be any more pictures, though, since they take up too much bandwidth and would take too long to send home. Instead, the live stream will consist of information about the makeup of the dust and gas in Saturn’s atmosphere, measurements of the planet’s magnetic field, and data in radio, infrared, and ultraviolet wavelengths.

“As we fly through the atmosphere, we are able to literally scoop up some molecules, and from those we can figure out the ground truth in Saturn’s atmosphere,” says Scott Edgington, a Cassini project scientist. “Just like almost everything else in this mission, I expect to be completely surprised.”

While many of Cassini’s most unexpected discoveries were related to Saturn’s moons, especially the water worlds Enceladus and Titan, it has also unveiled some mysteries on the ringed planet itself.

Saturn’s stormy nature



In 2007, images from Cassini revealed a colossal hexagonal feature at Saturn’s north pole which had only been partially glimpsed by the Voyager 1 and 2 spacecraft. They also showed hurricanes thousands of kilometres across at both poles, but it’s not yet clear what powers those huge storms.

The mission also found strangeness in Saturn’s magnetic and gravitational fields that nobody has yet been able to explain. “We’re finding that Saturn is complicated on the inside, and to date the leading models have been shown to be wrong,” says Edgington.

More recently, as the craft swooped between Saturn’s rings and the planet for the first time, it found a surprising lack of large ice particles in the gap. Some particles do fall from the rings into the atmosphere in a phenomenon called ring-rain, though, and researchers hope that Cassini may be able to learn more about the interactions between the rings and the planet during its final descent.