As Cassini’s tour of Saturn draws to a close, a look back at postcards from the probe

NASA's veteran spacecraft has revealed a lot about Saturn in its more than 20 years in space

Take a bow, Cassini. It’s been a marathon performance: 20 years in space, more than 200 orbits around Saturn, and hundreds of thousands of images of the giant planet, its splashy rings and its many moons. On September 15, the veteran spacecraft will use its last burst of fuel to plunge into the sixth planet from the sun. Scientists and space enthusiasts around the world will watch it go with awe and nostalgia.

“It’s hard not to anthropomorphize the spacecraft,” says Matthew Tiscareno of the SETI Institute in Mountain View, Calif., who has been working on Cassini since it entered Saturn’s orbit in 2004. “We’ve been riding on its back for these 13 years, and it’s done everything we’ve asked. I think it’s the most spectacularly successful mission that NASA has ever run.”

Cassini was designed to train its 12 scientific instruments on the Saturn system for a short four years, but NASA extended the mission twice. Even with the extra time, Cassini’s 13-year run is less than half of a year on Saturn, where a year lasts 29 Earth years.

Gas swirl

Saturn’s north pole was dark when Cassini arrived in 2004. But as the seasons changed, light illuminated a bizarre six-sided swirl of gases at the pole (shown here in false color). The hexagon, known since the 1980s, is about 30,000 kilometers wide with a massive hurricane centered on the north pole (SN: 1/11/14, p. 10).

After all this time, we’ve witnessed only the transitions to Saturnian spring and summer, the equivalent of January to June on Earth. And yet we’ve seen so much.

Cassini has revealed massive churning storms that rage for decades, rings that may be the best laboratory for studying how planets form and details of some of Saturn’s more than 60 moons. Two of those satellites, Titan and Enceladus, surprised Cassini scientists by having many of the right ingredients for life (SN: 9/2/17, p. 12). The craft has revamped our picture of Saturn and its celestial family.

Saturn’s potentially habitable moons are the reason Cassini must meet a dramatic end. The Cassini mission team decided it was safer to crash the craft into Saturn itself than to risk the craft wandering off and brushing up against Enceladus or Titan, spreading its earthly germs to any nascent ecosystems there.

But the craft will be busy until the very end. Since April, Cassini has been making weekly dives into the possibly rubble-strewn region between Saturn and its rings, a zone the team hadn’t dared explore before. Plus, the craft will collect data during its last hurtle into the gas giant’s atmosphere. Those final measurements should help solve some of the most basic mysteries about the planet, including when it got its iconic rings.

“Cassini data,” says team member Ralph Lorenz of the Applied Physics Lab, “is going to keep us busy for decades.”