spaceSpace and Physics

Cassini Is About To Brush Saturn’s Atmosphere For The First Time


Jonathan O'Callaghan

Senior Staff Writer


If you weren’t enjoying 2017 already, things are about to get a lot worse. The Cassini spacecraft will orbit Saturn just five more times before the mission ends in September.

The first of these final five passes begins this Sunday, August 13. Cassini will fly just 1,700 kilometers (1,050 miles) from the cloud tops of Saturn, getting closer to the atmosphere than ever before.


During this fly past, it’s expected to pass through enough of the atmosphere that it’ll need to use its small thrusters to prevent atmospheric drag. This also happened during flybys of Saturn’s moon Titan, the last of which was in April.

This is the first time Cassini, which entered orbit around Saturn in 2004, will brush the atmosphere of Saturn. Getting so close, it will perform the first ever direct sample of Saturn’s atmosphere, using its Ion and Neutral Mass Spectrometer (INMS). This will measure the density of molecular hydrogen, helium, and various ions. Yes, that’s awesome.

On this orbit, number 288, Cassini will also use its Composite Infrared Spectrometer (CIRS) to observe the edge of Saturn’s atmosphere and work out the different temperatures at different heights. It will also use its camera to try and spot mysterious “streaks” in Saturn’s C ring.

"As it makes these five dips into Saturn, followed by its final plunge, Cassini will become the first Saturn atmospheric probe," said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL), in a statement. "It's long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we're laying the groundwork for future exploration with this first foray."


The team will use this flyby to plan the final four orbits. If the atmosphere is more dense than expected, and the thrusters have to work harder, then the height of each subsequent orbit will be increased by about 200 kilometers (120 miles). This is known as a “pop-up maneuver”.

If it’s less dense than expected, then the team will do an opposite maneuver – a pop-down. This will see Cassini’s orbit lowered by 200 kilometers (120 miles), letting it get even more data on the atmosphere.

Ultimately, the mission will come to an end on September 15. Using Titan’s gravity to alter its trajectory, Cassini’s path will be bent to plunge more directly into the atmosphere.

It will continue sending data until the struggle of pointing its antenna towards Earth against the pressure of the atmosphere becomes too great. Then it will break apart, and the 20-year mission that launched in 1997 will be over.


I’m not crying. You’re crying.


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