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Saturn’s rings are halfway to their death

A composite image from 2009 made available by NASA shows Saturn in equinox as seen by the approaching Cassini spacecraft. Saturn’s equinox occurs only once in about 15 Earth years. (NASA/JPL/Space Science Institute/AP) (AP)

If dinosaurs had possessed telescopes and the will to gaze skyward 100 million years ago, they might have seen a very different Saturn — one without its iconic rings.

And if humans manage to survive another 100 million years, our descendants may also miss the discs of ice and dust that encircle the golden gas giant.

We live in an extraordinary era, scientists say — the brief blip in the 4.6-billion-year life of our solar system in which Saturn’s rings are visible. According to a study published this week in the planetary science journal Icarus, the material that makes up this feature is “raining” into the planet’s interior at a “worst case scenario” rate. The rings are already halfway to their death.

“We are lucky to be around” right now, the study’s lead author, James O’Donoghue, said in a statement.

Scientists have long debated whether Saturn’s rings were born with the planet or are a relatively new acquisition. Some models suggest that the ring material is debris left over from the planet’s formation more than 4 billion years ago. But others theorize that the rings formed when objects like comets, asteroids or even moons broke apart in orbit around the massive planet.

It’s hard to imagine the sixth planet from the sun without its most famous feature. Though Jupiter, Uranus and Neptune are also banded, Saturn’s adornment is by far the most impressive in the solar system. The planet’s rings span 170,000 miles across and are bright enough to be visible with a child’s telescope.

And although they look solid from Earth, observations by the Voyager and Cassini spacecraft have revealed that the rings are instead made of floating bits of material, ranging in size from as small as specks to larger than the Empire State Building. They stay suspended around the planet’s midsection through a careful balance of gravity, which tries to pull the material inward, and their orbital velocity, which seeks to sling them into space.

But sometimes ring particles get electrically charged by light from the sun or other cosmic phenomena. This makes them susceptible to the siren song of Saturn’s magnetic field, which bends inward at the rings. The particles slide along magnetic field lines into the planet’s atmosphere, where they vaporize, generating glowing, charged hydrogen and droplets of water.

O’Donoghue and his colleagues observed this phenomenon with the huge Keck telescope in Hawaii and concluded that a combination of Saturn’s gravity and magnetism pulls an Olympic-size swimming pool worth of material into the planet every 30 minutes. Combining this analysis with data collected by the departed Cassini spacecraft, which dove through the rings before plunging into Saturn last year, O’Donoghue predicts that the rings have less than 100 million years to live.

Look up while you can.

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