It's been a good 19 years, but now Cassini must die.
This week, the NASA spacecraft will hurl itself into the atmosphere of the planet it's spent over a decade circling in search of solar system secrets hidden from human view until the orbiter arrived on the scene.
Cassini will enter Saturn's atmosphere on Friday for the first time, firing its thrusters until it gets tumbled around by the increasing density of the gas giant's outer layers. At that point the spacecraft, which is roughly the size and weight of a school bus, will likely lose its communications link with NASA and begin burning up.
The decision to destroy the probe has to do with. Thanks to the epic Cassini mission, we now know that some of those . We wouldn't want to mess with the first aliens we may find by leaving our out-of-control space junk careening around the neighborhood, especially Cassini with its onboard nuclear-powered generator.
"Cassini's grand finale is both exciting and bittersweet," Planetary Society CEO and famed "science guy" Bill Nye said in a statement. "Rest assured, the mission's science will carry on long after the spacecraft's farewell crash and end."
When Cassini launched from Cape Canaveral, Florida, on Oct. 15, 1997, use of the words "Tubthumping" and "Chumbawumba" was at an all-time high, a youth named Harry Potter, and the domain name for a website with the weird name "Google" had just been registered.
Over the course of its 20-year mission, the craft has made 294 orbits of the ringed planet, taking almost half a million images and collecting over 600GB of data. The information Cassini gleaned contributed to nearly 4,000 published scientific papers. Some 5,000 people have worked on the mission over the years, according to NASA.
"I think Cassini will mostly be remembered for broadening our thinking about what habitability means in the solar system," Cassini's lead propulsion engineer Todd Barber said. "The entire concept of 'ocean worlds' as revealed by Cassini and [earlier NASA probe] Galileo may well drive future outer planet exploration. In fact, it's possible the most promising place to look for life in the solar system outside of Earth is among these oceans worlds in the outer solar system."
Cassini discovered oceans on Saturn's moons Titan and Enceladus, as well as six new named moons. The craft alsoshooting out of the icy crust of Enceladus and detected evidence of the building blocks of life in a sample of the spray.
But now, as anticipated, the fuel for the nuclear reactor is almost spent and there's no way to refuel.
You might point out that slamming a spacecraft into Saturn doesn't seem like the best way to protect potential Saturnian life, but NASA says it's got that covered. According to the NASA's end-of-mission FAQ:
"Any spacecraft material that survives atmospheric entry, potentially including its radioisotope fuel, will sink deep into the planet where it will melt and become completely diluted as it mixes with the hot, high-pressure atmosphere of the giant planet."
So that's how Cassini will end, but here's how the well-traveled robot will spend its final two days in this universe.
The beginning of the end started Tuesday when Cassini sent back data from its final pass by.
On Thursday afternoon, just before 1 p.m. PT, the ship will take what might be its final goodbye images. About 25 minutes later, it will turn its antenna toward Earth and start sending back its last shipment of data. NASA says the communications link with Cassini will stay open continuously for the remaining 14 or so hours of its mission, right up until it goes dark.
Among the data that mission controllers plan to receive through this channel is information about Saturn's atmosphere, gathered by pointing Cassini's ion and neutral mass spectrometer at the planet on close approach, just before it passes the planet's famous rings. This could determine the composition of Saturn's outer atmosphere and offer at least a digital taste of what it might be like to crash headlong into arguably the most beautiful planet we know of (so far).
At roughly 3:30 a.m. PT Friday, Cassini should begin entering Saturn's atmosphere. At this point, the probe will execute a command from the Cassini flight team at NASA's Jet Propulsion Laboratory in Pasadena, California.
But unlike the more than 2.5 million commands that preceded it, this final directive will instruct the craft to charge ahead into oblivion. It will turn its thrusters on full blast until Earth loses the craft's signal and it presumably burns up like a meteor well over 700 million miles away.
A finely engineered metal meteor, that is, that changed how humanity looks at this surprisingly bizarre solar system we live in: whether it's theor the enticing plumes of Enceladus, Cassini showed us there's still much to discover about our corner of the galaxy.
Enjoy that final blaze of glory, you resilient little robot.
Below, you can watch NASA's live coverage of Cassini's end to catch its final images, which are expected to come through later Thursday, and follow it right up to the moment its signal goes quiet Friday morning.
First published Sept. 13, 7 a.m. PT.
Update, Sept. 14 at 11 a.m. PT: Adds information on how to watch NASA's stream live.
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