A selection of photographs taken by Cassini. Photos: NASA/JPL-Caltech/Space Science Institute
The Cassini spacecraft has been in orbit around Saturn for 13 years, beaming data and photographs back to Earth. When it deliberately dove into Saturn's atmosphere today, it marked the end of one of our most in-depth looks at an alien planet to date and our only link to the Saturnian system. There are no plans to return.
The mission might be over, but there are discoveries yet to come as scientists sift through over 635 gigabytes of data sent back to Earth. Although we're certainly leaving out some (shoutout to Pan, the ravioli-shaped moon that took the internet by storm), here are three top findings so far.
1. Moons that could harbor life
Enceladus, the icy ocean moon. Cassini revealed that under Enceladus' icy surface there is a vast salty ocean, and plumes of it erupt from the South Pole like geysers. This discovery "changed almost the entire focus of the mission," writes JoAnna Wendel for Eos, because liquid water could mean life.
- When Cassini flew through the plume, scientists detected molecular hydrogen, which means there are probably hydrothermal vents at the bottom of Enceladus' sea. Some scientists think life on Earth began on vents like those.
Titan, the gassy moon. A previous flyby from the Voyager spacecraft had shown that Titan had an atmosphere, so European Space Agency scientists created Huygens, a probe delivered by Cassini and dropped on Titan to sample the surroundings. It found vinyl cyanide, a complex molecule that some think could be a building block for alien life, as well as methane clouds, lakes and rivers: something akin to the water cycle on earth, but with methane instead of water.
And possibly more. Not all of Cassini's data has been analyzed, but there's some evidence that the tiny moon Dione has an internal ocean.
Why it matters: Along with Jupiter's Europa, Titan and Enceladus have redefined where we might find life beyond Earth.
2. Details about Saturn's rings
Once thought to be flat, Cassini's pictures revealed the dynamic landscape of Saturn's rings. There are dramatic spikes a mile and a half tall. Density waves form ripples in the rings, which come from the same processes that make the spirals in our own galaxy. And there's an empty gap between the rings and Saturn that Cassini dove through to record what it sounds like.
Why it matters: Tiny, propeller-like moons-to-be are scattered throughout these structures. They provide a glimpse into the early days of our solar system, when planets may have been propellers in a dustcloud around our Sun.
3. Some mind-blowing pictures
- Incredible images of Jupiter.
- Half-blue Saturn, a startling image that revealed how the planet's color changes with the seasons.
- A massive storm forming in the planet's tumultuous atmosphere
- Saturn backlit by the sun.
- And of course, this iconic photograph of The Day The Earth Smiled.
What's next: As Cassini falls towards Saturn, it'll sample the planet's atmosphere and take a few key readings. So far, scientists have struggled to get the magnetic measurements necessary to determine the length of a Saturnian day — but Cassini's last transmissions might contain that key data.
Go deeper:
- Shannon Stirone explains what it takes to kill a spacecraft for The Atlantic. "Thousands will gather at JPL and wait until the early morning hours for Cassini's final orbit to begin. They'll share stories of a lifetime of work, as that effort culminates in fireworks 800 million miles away."
- At the LA Times, Linda Netburn writes about how Cassini came to be. "This is the story of how it got off the ground, told by the people who were there."
- Science News' Lisa Grossman highlights some of the best 'postcards' Cassini sent back to Earth: "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."