Farewell to the Cassini probe, America's emissary to Saturn


NASA flight planners have a long history of murdering their favorite space probes. They plan the ships, they build the ships — and at some point they wind up killing the ships.

The Ranger probes — the first NASA spacecraft to touch the moon—were crash-landers. They were designed for one job: to fly straight toward the lunar face, switch on their cameras in the final 14 minutes of their journey, when they were just 1,500 miles from the surface, and then capture as many pictures as they could before vaporizing themselves in a violent, fireless crash on the moon’s airless surface. The Messenger probe, which circled Mercury for four years from 2011 to 2015, met a similarly nasty end, sent to a deliberate crash landing when it was almost out of fuel so it could collect the most close-up data possible before it became a drifting piece of space junk.

On Sept. 15, at 7:55 AM EDT, the Cassini Saturn probe will follow its sisters into history, plunging to its end in Saturn’s atmosphere. But in this case, the death of the ship might actually save lives — Saturnian lives.

Long before Cassini left Earth on October 15, 1997, astronomers knew that Saturn’s largest moon, Titan, was probably rich in liquid methane and ethane — hydrocarbons essential for life as we know it. Cassini confirmed that. The spacecraft also discovered that Enceladus, a smaller, ice-covered moon, emits periodic water geysers from its south pole. That almost certainly means a comparatively warm, salty ocean just beneath the moon’s frozen rind. Where there is salty, liquid water, there could be living things.

As an emissary from Earth, however, Cassini could be carrying trace organisms — or at least organic material. And since the ship, like Messenger, is running out of fuel, there is always a chance it could eventually crash into one of those promising worlds, contaminating an alien ecosystem with residue from the Earthly one. So the ship instead will give itself up to the crushing pressure and annihilating winds of the atmosphere of Saturn, the lifeless mother of those potentially living moons.

MORE: These Stunning Photos of Saturn Are a Beautiful Goodbye From NASA’s Cassini Probe

Cassini’s 20-year career will have been exceedingly well-spent. In an era of tight NASA budgets, it was one of the space agency’s rare Cadillac probes — a six-ton, 22-ft.-long, $3.25 billion beast of a thing, muscled off the pad by a Titan IV heavy-lift rocket. The ship took seven…


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