Scientists from NASA have discovered that Saturn's rings are disappearing at a rapid pace.

This is being done through a process called "ring rain" - which means the rings are being pulled into Saturn by gravity as a dusty 'rain' of ice particles under the planet's magnetic field.

James O'Donoghue is from NASA's Goddard Space Flight Centre.

"We estimate that this 'ring rain' drains an amount of water products that could fill an Olympic-sized swimming pool from Saturn's rings in half an hour.

"From this alone, the entire ring system will be gone in 300 million years, but add to this the Cassini-spacecraft measured ring-material detected falling into Saturn's equator, and the rings have less than 100 million years to live.

"This is relatively short, compared to Saturn's age of over four billion years."

The new research suggests the rings were acquired later in life then when the planet formed - they are unlikely to be older than 100 million years.

"We are lucky to be around to see Saturn's ring system, which appears to be in the middle of its lifetime.

"However, if rings are temporary, perhaps we just missed out on seeing giant ring systems of Jupiter, Uranus and Neptune, which have only thin ringlets today" Mr O'Donoghue added.

Various theories have been proposed for the ring's origin.

One is if the planet got them later in life, the rings could have formed when small, icy moons in orbit around Saturn collided, perhaps because their orbits were perturbed by a gravitational tug from a passing asteroid or comet.

The first hints that 'ring rain' existed came from Voyager observations in images of Saturn's upper atmosphere made in 1981.

In 1986, Jack Connerney of NASA Goddard published a paper that linked those narrow dark bands to the shape of Saturn's enormous magnetic field, proposing that electrically charged ice particles from Saturn's rings were flowing down invisible magnetic field lines, dumping water in Saturn's upper atmosphere where these lines emerged from the planet.

The influx of water from the rings, appearing at specific latitudes, washed away the stratospheric haze, making it appear dark in reflected light, producing the narrow dark bands captured in the Voyager images.

Saturn’s moon Enceladus drifts before the rings and the tiny moon Pandora in this view that NASA's Cassini spacecraft captured on November 1st, 2009 | Image: NASA/JPL-Caltech/Space Science Institute

Saturn's rings are mostly chunks of water ice ranging in size from microscopic dust grains to boulders several meters across.

NASA says ring particles are caught "in a balancing act" between the pull of Saturn's gravity, which wants to draw them back into the planet, and their orbital velocity, which wants to fling them outward into space.

Tiny particles can get electrically charged by ultraviolet light from the Sun or by plasma clouds emanating from micrometeoroid bombardment of the rings.

When this happens, the particles can feel the pull of Saturn's magnetic field, which curves inward toward the planet at Saturn's rings.

In some parts of the rings, once charged, the balance of forces on these tiny particles changes dramatically, and Saturn's gravity pulls them in along the magnetic field lines into the upper atmosphere.

Once there, the icy ring particles vaporise and the water can react chemically with Saturn's ionosphere.

Mr O'Donoghue's team also discovered a glowing band at a higher latitude in the southern hemisphere.

This is where Saturn's magnetic field intersects the orbit of Enceladus, a geologically active moon, indicating that some of those particles are raining onto Saturn as well.

"That wasn't a complete surprise," said Connerney.

"We identified Enceladus and the E-ring as a copious source of water as well, based on another narrow dark band in that old Voyager image."

The team would like to see how the ring rain changes with the seasons on Saturn.

As the planet progresses in its 29.4-year orbit, the rings are exposed to the Sun to varying degrees.

Since ultraviolet light from the Sun charges the ice grains and makes them respond to Saturn's magnetic field, varying exposure to sunlight should change the quantity of ring rain.