NASA's Cassini probe is about to plunge to its doom — and its fiery death may be visible to telescopes on Earth

NASA's Cassini probe has orbited Saturn for over a decade. This Friday, scientists will steer it into the gas giant's atmosphere.

NASA/JPL-Caltech/Space Science Institute

After 13 years in orbit around Saturn, NASA's Cassini spacecraft is about to plunge itself into the planet's atmosphere and disintegrate. NASA decided to put an end to the mission on Friday because the probe is almost out of fuel.
Cassini has provided exquisite details about the second-largest planet in our solar system.
Take the hurricanes at Saturn's poles, for example. "These hurricanes are large enough they'd cover about half the continental United States, about 50 times larger than a typical Earth hurricane," says Cassini project scientist Linda Spilker of NASA's Jet Propulsion Laboratory.
Then there are the remarkable, hexagonal-shaped jet streams at the north pole. They've been there since before Cassini arrived in 2004.
"We have jet streams here on the Earth, but they change almost daily," Spilker says. "So we're really puzzled. It's the only place we know of in our solar system that has a long-lived hexagonal jet stream."

Cassini has observed a strange, hexagonal jet stream at Saturn's north pole.

NASA/JPL-Caltech/Space Science Institute

Spilker's special interest is Saturn's rings, and she says Cassini has revealed some unexpected things about them. There are places, for example, where the particles that form the rings clump together.
"The clumpiness has a unique character. Sometimes it looks kinda clumpy and speckly, other times it looks streaky," she says. And in other places, the particles float freely and don't appear to have any structure.

"How you can keep those areas separated?" she says. "That's an interesting and curious puzzle."
For all that Cassini has revealed about Saturn, there are still plenty of mysteries.
"It's a little bit embarrassing to confess, but we don't know how long a day is on Saturn," says Michele Dougherty of Imperial College in London. She's the scientist in charge of Cassini's magnetometer, an instrument that measures Saturn's magnetic field.
"In some ways," she says, "you can almost use a magnetometer to see inside a planet and get a better understanding of its internal structure."
Cassini's final orbits are taking it closer to the planet than ever before. Dougherty is hoping this will let her instrument see a telltale tilt in the magnetic field that should resolve the uncertainty over the length of a Saturnian day. "If we don't, we might not be able to work out the exact length of a day is on Saturn," she says.
Some of Cassini's most interesting discoveries involve Saturn's moons.
Take Enceladus.