
Nasa's Cassini spacecraft is about to begin series of 20 orbits high above and below Saturn's poles.

Plunging just past the outer edge of the main rings, the orbits will mark the last phase of Cassini's mission.

While it passes through Saturn's famous rings, Cassini will collect samples of particles and gases and get the best view yet of the tiny, hard-to-spot moons found near the rings.

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Nasa's Cassini spacecraft is about to begin series of 20 orbits high above and below Saturn's poles. Plunging just past the outer edge of the main rings, the orbits will mark the last phase of Cassini's mission. Saturn's northern hemisphere in 2016 is pictured, taken by Cassini

THE CASSINI MISSION Since it left earth in 1997 and arrived at Saturn in 2004, Cassini has been touring the system with an up-close study of the planet, its rings and moons. During its journey, Cassini has made dramatic discoveries, including a global ocean within Enceladus and liquid methane seas on Titan. After nearly 20 years in space, the mission is drawing near its end because the spacecraft is running low on fuel. Advertisement

On the 30 November, following a gravitational nudge from Saturn's moon Titan, Cassini will enter this new orbiting phase, that will last until 22 April next year.

'We're calling this phase of the mission Cassini's Ring-Grazing Orbits, because we'll be skimming past the outer edge of the rings,' said Linda Spilker, Cassini project scientist at Nasa's Jet Propulsion Laboratory, Pasadena, California.

'In addition, we have two instruments that can sample particles and gases as we cross the ringplane, so in a sense Cassini is also 'grazing' on the rings.'

Instruments on board the spacecraft will take direct samples of particles in the rings and molecules of gases found close by.

In the first two orbits, Cassini will fly through a faint ring, that was produced when a meteor struck two of Saturn's small moons.

Grazing the edges of the rings will provide some of the closest-ever studies of the outer portions of Saturn's main rings - the A, B and F rings.

In March and April next year, the spacecraft will pass through the dusty reaches of the F ring.

'Even though we're flying closer to the F ring than we ever have, we'll still be more than 4,850 miles (7,800 km) distant. There's very little concern over dust hazard at that range,' said Earl Maize, Cassini project manager at JPL.

The F ring marks the outer boundary of the main ring system even though Saturn has several other, much fainter rings that lie further away from the planet.

This distant ring is complex and constantly changing - with Cassini images showing structures like bright streamers, wispy filaments and dark channels appearing and developing over just a matter of hours.

The ring is also quite narrow, only about 500 miles (800 km), wide with a denser region about 30 miles (50 km) wide at its core.

Grazing the edges of the rings will provide some of the closest-ever studies of the outer portions of Saturn's main rings (the A, B and F rings) NASA/JPL-Caltech/Space Science Institute

On the 30 November, following a gravitational nudge from Saturn's moon Titan, Cassini will enter this new orbiting phase, that will last until 22 April next year. Saturn's biggest and brightest moons are visible in this portrait by Cassini released by NASA 14 March, 2005. Titan (5,150 kilometers, or 3,200 miles across) is Saturn's largest moon and appears at the lower left

WHAT'S NEXT FOR CASSINI: THE MOON GRAZING PHASE On the 30 November, following a gravitational nudge from Saturn's moon Titan, Cassini will enter this new orbiting phase, that will last until 22 April next year. While it passes through Saturn's famous rings, Cassini will collect samples of particles and gases and get the best view yet of the tiny, hard-to-spot moons found near the rings. In the first two orbits, Cassini will fly through a faint ring, that was produced when a meteor struck two of Saturn's small moons. Instruments on board the spacecraft will take direct samples of particles in the rings and molecules of gases found close by. In March and April next year, the spacecraft will pass through the dusty reaches of the F ring. The mission will also investigate small-scale features in the A ring called 'propellers,' which reveal the presence of unseen moonlets, or tiny moons. Cassini's ring-grazing orbits will also allow the spacecraft to study the small moons that orbit in or near the edges of the rings including Pandora, Atlas, Pan and Daphnis. On top of this, Cassini will observe Saturn's atmosphere during the ring-grazing phase of the mission to more precisely determine how far it extends above the planet. Advertisement

Since it left earth in 1997 and arrived at Saturn in 2004, Cassini has been touring the system with an up-close study of the planet, its rings and moons. During its journey, Cassini has made dramatic discoveries, including a global ocean within Enceladus and liquid methane seas on Titan. Artist's impression pictured

THE GRAND FINALE After nearly 20 years in space, the mission is drawing near its end because the spacecraft is running low on fuel. The Cassini team carefully designed the finale to conduct an extraordinary science investigation before sending the spacecraft into Saturn, to protect its potentially habitable moons. During its grand finale, Cassini will pass as close as 1,012 miles (1,628 km) above the clouds as it dives repeatedly through the narrow gap between Saturn and its rings, before making its mission-ending plunge into the planet's atmosphere on 15 September next year. Advertisement

The mission will investigate small-scale features in the A ring called 'propellers,' which reveal the presence of unseen moonlets, or tiny moons.

Because of their propeller-like shapes, scientists have given some of the more persistent features informal names inspired by famous aviators, including 'Earhart'.

Observing propellers at high resolution will likely reveal new details about their origin and structure.

Cassini's ring-grazing orbits will also allow the spacecraft to study the small moons that orbit in or near the edges of the rings including Pandora, Atlas, Pan and Daphnis.

The probe will also observe Saturn's atmosphere during the ring-grazing phase of the mission to more precisely determine how far it extends above the planet.

After nearly 20 years in space, the mission is drawing near its end because the spacecraft is running low on fuel.

The Cassini team carefully designed the finale to conduct an extraordinary science investigation before sending the spacecraft into Saturn, to protect its potentially habitable moons.

During its grand finale, Cassini will pass as close as 1,012 miles (1,628 km) above the clouds as it dives repeatedly through the narrow gap between Saturn and its rings, before making its mission-ending plunge into the planet's atmosphere on 15 September next year.