NASA's Saturn-orbiting Cassini spacecraft faces fiery finish

After a 20-year voyage, NASA's Cassini spacecraft is poised to dive into Saturn this week to become forever one with the exquisite planet.

There's no turning back: Friday it careens through the atmosphere and burns up like a meteor in the sky over Saturn.

NASA is hoping for scientific dividends up until the end. Every tidbit of data radioed back from Cassini will help astronomers better understand the entire Saturnian system — rings, moons and all.

FILE - In this Friday Sept. 20, 1996 file photo, NASA's Jet Propulsion Laboratory engineers and technicians lower the 3,420-pound Cassini Spacecraft into the Launch-Vehicle-Adapter at JPL in Pasadena, Calif. After a 20-year voyage, the spacecraft is poised to dive into Saturn on Friday, Sept. 15, 2016. (AP Photo/Frank Wiese)

The only spacecraft ever to orbit Saturn, Cassini spent the past five months exploring the uncharted territory between the gaseous planet and its dazzling rings. It's darted 22 times between that gap, sending back ever more wondrous photos.

On Monday, Cassini flew past jumbo moon Titan one last time for a gravity assist— a final kiss goodbye, as NASA calls it, nudging the spacecraft into a deliberate, no-way-out path.

During its final plunge early Friday morning, Cassini will keep sampling Saturn's atmosphere and beaming back data, until the spacecraft loses control and its antenna no longer points toward Earth. Descending at a scorching 76,000 mph (122,000 kph), Cassini will melt and then vaporize. It should be all over in a minute.

This Feb. 3, 2017 image made available by NASA shows Saturn's shadow on its rings as seen from the Cassini spacecraft. (NASA/JPL-Caltech/Space Science Institute via AP)

"The mission has been insanely, wildly, beautifully successful, and it's coming to an end," said NASA program scientist Curt Niebur. "I find great comfort in the fact that Cassini will continue teaching us up to the very last second."

Telescopes on Earth will watch for Cassini's burnout nearly a billion miles (1.6 billion kilometers) away. But any flashes will be hard to see given the time — close to high noon at Saturn — and Cassini's minuscule size against the solar system's second largest planet.

The plutonium on board will be the last thing to go. The dangerous substance was encased in super-dense iridium as a safeguard for Cassini's 1997 launch and has been used for electric power to run its instruments. Project officials said once the iridium melts, the plutonium will be dispersed into the atmosphere. Nothing — not even traces of plutonium — should escape Saturn's deep gravity well.

The whole point of this one last exercise — dubbed the Grand Finale — is to prevent the spacecraft from crashing into the moons of Enceladus (ehn-SEHL'-uh-duhs) or Titan. NASA wants future robotic explorers to find pristine worlds where life might possibly exist, free of Earthly contamination.

It's inevitable that the $3.9 billion U.S.-European mission is winding down. Cassini's fuel tank is almost empty, and its objectives have been accomplished many times over since its 2004 arrival at Saturn following a seven-year journey.

The leader of Cassini's imaging team, planetary scientist Carolyn Porco, already feels the loss.

"There's another part of me that's just, 'It's time. We did it.' Cassini was so profoundly, scientifically successful," said Porco, a visiting scholar at the University of California, Berkeley. "It's amazing to me even, what we were able to do right up until the end."

Until Cassini, only three spacecraft had ventured into Saturn's neighborhood: NASA's Pioneer 11 in 1979 and Voyager 1 and 2 in the early 1980s. Those were just flybys, though, and offered fleeting glances. And so Cassini and its traveling companion, the Huygens (HOY'-gens) lander, actually provided the first hard look at Saturn, its rings and moons. They are named for 17th-century astronomers, Italian Giovanni Domenico Cassini and Dutch Christiaan Huygens, who spotted Saturn's first moon, Titan. The current count is 62.

Cassini discovered six moons — some barely a mile or two across — as well as swarms of moonlets that are still part of Saturn's rings.

All told, Cassini has traveled 4.9 billion miles (7.9 billion kilometers) since launch, orbited Saturn nearly 300 times and collected more than 453,000 pictures and 635 gigabytes of scientific data.

The European Space Agency's Huygens lander — which hitchhiked all the way to Saturn aboard Cassini — still rests on Titan. It parachuted down in 2005, about six months after Cassini arrived at Saturn, and relayed data for more than an hour from the moon's frigid surface.

Still believed intact, Huygens remains the only spacecraft to actually land in one of our outer planetary systems.

This July 23, 2008 image made available by NASA shows the planet Saturn, as seen from the Cassini spacecraft. After a 20-year voyage, Cassini is poised to dive into Saturn on Friday, Sept. 15, 2016. (NASA/JPL/Space Science Institute via AP)

Other than Titan's size — about as big as Mercury — little was known about Saturn's biggest and haze-covered moon before Cassini and Huygens showed up. They revealed seas and lakes of methane and ethane at Titan — the result of rainfall — and provided evidence of an underground ocean, quite possibly a brew of water and ammonia.

Over at the little moon Enceladus, Cassini unveiled plumes of water vapor spewing from cracks at the south pole. These geysers are so tall and forceful that they actually blast icy particles into one of Saturn's rings. Thanks to Cassini, scientists believe water lies beneath the icy surface of Enceladus, making it a prime spot to look for traces of potential life.

"Enceladus has no business existing and yet there it is, practically screaming at us, 'Look at me. I completely invalidate all of your assumptions about the solar system.'" Niebur said. "It's an amazing destination."

That's precisely why scientists didn't want to risk Cassini crashing into it, said program manager Earl Maize at NASA's Jet Propulsion Laboratory in Pasadena, California.

"The book is not complete. There's more to come" from exploring the planets, Maize said. "But this has been a marvelous ride."

UNITED NATIONS (AP) — Russia and Ukraine on Monday traded blame before the United Nations Security Council for the attacks on Europe’s largest nuclear power plant, which the head of the International Atomic Energy Agency said have put the world “dangerously close to a nuclear accident.”

Without attributing blame, IAEA Director General Rafael Mariano Grossi said his agency has been able to confirm three attacks against the Zaporizhzhia Nuclear Power Plant since April 7.

“These reckless attacks must cease immediately,” he told the Security Council. “Though, fortunately, they have not led to a radiological incident this time, they significantly increase the risk … where nuclear safety is already compromised.”

The remote-controlled nature of the drones that have attacked the plant means that it is impossible to definitively determine who launched them, Grossi told reporters after the meeting.

“In order to say something like that, we must have proof,” he said. “These attacks have been performed with a multitude of drones.”

Zaporizhzhia sits in Russian-controlled territory in southeastern Ukraine and has six nuclear reactors.

Fears of a nuclear catastrophe have been at the forefront since Russian troops occupied the plant shortly after invading in February 2022. Continued fighting between Russian and Ukrainian forces — as well as the tense supply situation at the plant — have raised the specter of a disaster.

Ukraine and its allies on Monday again blamed Russia for dangers at the site, with the United States saying, “Russia does not care about these risks.”

“If it did, it would not continue to forcibly control the plant,” U.S. deputy ambassador Robert Wood told the Security Council, which met at the initiative of the U.S. and Slovenia.

Russia, for its part, said Ukraine was to blame for the attacks.

“The IAEA’s report does not pinpoint which side is behind the attacks,” Russia’s U.N. Ambassador Vassily Nebenzia said. “We know full well who it is.”

“Over the last few months, such attacks not only resumed,” Nebenzia said, “they significantly intensified.”

Ukraine’s ambassador to the U.N., Sergiy Kyslytsya, called the attacks “a well-planned false flag operation by the Russian Federation,” which he alleged Russia had designed to distract the world from its invasion of its neighbor.

The Zaporizhzhia facility is one of the 10 biggest nuclear plants in the world. Fighting in the southern part of Ukraine where it is located has raised the specter of a potential nuclear disaster like the one at Chernobyl in 1986, where a reactor exploded and blew deadly radiation across a vast area.

Neither Russia nor Ukraine in recent months has been able to make significant advances along the 1,000-kilometer (620-mile) front line crossing eastern and southern Ukraine. Drones, artillery and missiles have featured heavily in what has become a war of attrition.

Russia and Ukraine have frequently traded accusations over the Zaporizhzhia plant.

The most recent strikes did not compromise the facility, which is designed to withstand a commercial airliner crashing into it, the IAEA said.

The plant’s six reactors have been shut down for months, but it still needs power and qualified staff to operate crucial cooling systems and other safety features.

FILE - The Zaporizhzhia nuclear power plant, Europe's largest, is seen in the background of the shallow Kakhovka Reservoir after the dam collapse, in Energodar, Russian-occupied Ukraine, Tuesday, June 27, 2023. Officials at the Russian-controlled Zaporizhzhia Nuclear Power Plant said that the site was attacked Sunday April 7, 2024, by Ukrainian military drones, including a strike on the dome of the plant’s sixth power unit. (AP Photo/Libkos, File)

IAEA warns that attacks on a nuclear plant in Russian-controlled Ukraine put the world at risk

IAEA warns that attacks on a nuclear plant in Russian-controlled Ukraine put the world at risk