NASA’s Cassini probe has been studying Saturn and its moons since 2005, and it’s almost time for the spacecraft to call it a day. The probe is running low on fuel, but scientists intend to get the most out of Cassini before it’s no longer capable of doing science. Earlier this year, mission managers at NASA’s Jet Propulsion Laboratory (JPL) kicked off the Grand Finale, which will eventually send Cassini spiraling into the clouds of Saturn. We’re about to get a little preview of that event as Cassini’s most recent dive at the gas giant sent it through the upper atmosphere, by far the closest it’s ever been to the planet.
Cassini has dropped into a lower orbit than its other recent passes, which were aimed as the gap between the innermost ring and the planet’s atmosphere. This is the first of five ultra-close orbits, which will eventually end in the satellite falling into the clouds, never to be seen again. The satellite skimmed just 1,600km (1,000 miles) above the cloud tops in the early morning Monday (GMT), giving it a taste of Saturn’s atmosphere.
Scientists believe about 75 percent of Saturn’s mass is hydrogen, with most of the remainder helium. Saturn is known to radiate more energy than it absorbs from the sun, so there’s a net loss of gravitational energy. Getting a more accurate measurement of gases in Saturn’s upper atmosphere by flying through it could help improve measurements of the planet’s inner composition. The data could also help to pin down the exact length of Saturn’s day.
In each successive pass, drag will pull Cassini further down into Saturn’s gravity well. That means it will need to run its thrusters to maintain a stable trajectory. When the data from its most recent pass is analyzed, JPL mission managers believe they will have the necessary data to send the probe lower on its next four orbits.
On September 15th, NASA expects the probe to crash into the atmosphere. For the time being, Cassini is still alive and sending back images. However, we’ll have to wait another day or two for the latest images to be sent back, as the probe makes another loop around the planet and gets its antenna oriented at Earth. The plan for Cassini’s final dive is to use what little fuel is left at that time to keep the antenna pointed at Earth for as long as possible. Hopefully, we’ll continue receiving data from the spacecraft right up until the end. Not only does this get us more data, but it also ensures that Cassini doesn’t one day crash-land on a moon like Enceladus, which some speculate could be home to microbial life.
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