Saturn, with its glorious rings, is the most operatic of all the planets. So what could be more fitting than for the Cassini spaceship, after more than a decade of exploring Saturn, its moons and its rings, to go out with a final, spectacular swan dive into the clouds of Saturn?
Every space mission must come to an end, including this 20-year mission to explore Saturn and its moons. The guidance system keeps the ship oriented so that its instruments can explore, while its radio antenna relays its findings back to Earth. But keeping the ship in position takes fuel — and Cassini’s fuel supply is running out.
Other interplanetary space missions have ended with the spacecraft drifting on into the depths of interstellar space. But Cassini is gravitationally bound to Saturn and would continue to orbit it indefinitely — or until the complex gravity field of Saturn and its dozens of moons perturbed its orbit so that it crashed into one of those moons.
Environmental Protection for Two Moons
This is something that NASA was determined should never happen, not even centuries into the future. Which is the real reason for Cassini’s swan dive into Saturn next month.
In its years exploring Saturn’s moons, Cassini found reason to suspect that two of Saturn’s moons, Titan and Enceladus, may harbor “prebiotic” chemical activity, complex thermal reactions that produce the building blocks of life. Or, Titan or Enceladus might be home to full-blown living organisms and ecosystems.
If there is even a chance of life, or almost-life, on these distant worlds, it is crucial to protect them against biological contamination originating from Earth.
Cassini carried a robotic passenger, Huygens, that landed on Titan in 2005. While Huygens was especially sterilized for its landing mission, no one yet realized when the mission was first designed that the Cassini spacecraft might also become an eventual contamination threat. So microbes might have slipped aboard as stowaways.
To present a risk, these stowaways would need to survive not only years in space but the bullet-speed impact of a collision.
But one thing we have learned is that life is both fantastically delicate and fantastically rugged. So to ensure that Saturn’s moons are protected from contamination, NASA mission commanders decided to plunge Cassini into Saturn itself.
Saturn has no solid surface, so there is nothing to crash into but an atmosphere that grows denser as you descend. Due to Saturn’s intense gravity, however, Cassini’s final dive will reach a much higher speed than a collision with a mere moon. The ship will burn up in the atmosphere like a meteor, vaporizing any stowaway microbes so that Saturn is safe from contamination.
Because the Cassini spaceship was not originally designed for this plunge, it will not be able to transmit data as far down into the atmosphere as the Galileo probe did when it took a pre-planned plunge into Jupiter in 1995. And the cameras will not record Cassini’s final moments — they require too much bandwidth for real-time transmission of images. But other instruments aboard Cassini will send back a stream of data until atmospheric drag sends the ship into a final tumble before it burns up.
What a gloriously operatic way to go!
This article was originally published on September 8, 2017.