Delighted with the success of its Cassini spacecraft, NASA has approved a two-year extension to the mission. The spacecraft will investigate hints that there is liquid water inside Saturn's moon Enceladus and explore uncharted territory on its exotic sibling Titan.

Cassini will also witness a dramatic alignment of Saturn's rings with the Sun. "It's going to look infinitely cool," says Carolyn Porco, who heads the spacecraft's imaging team. "This is something humans have never seen before."

Cassini has orbited Saturn since July 2004. Its original four-year mission was scheduled to end in July this year but, as expected, NASA announced on Tuesday that the healthy spacecraft's mission will continue. It should run until July 2010 or later.

Anticipating the decision, the mission team has drawn up a packed schedule of observations and moon flybys for the spacecraft.

Underground life

One of the most exciting targets is Enceladus, a 500-kilometre ball of ice and rock that astonished scientists with jets of water vapour spewing from hot spots at its south pole. The discovery hinted that liquid water might be present beneath the moon's icy surface, perhaps allowing life to have gained a foothold there.

But some scientists argue that the water vapour is merely due to warm ice sublimating – changing directly from solid to gas. "We're desperate to know whether the jetting activity that we see at the south pole is arising from bodies of liquid water," Porco told New Scientist.

Future observations by Cassini will help distinguish between the two possibilities. The team also plans to take the most detailed pictures yet of the source regions for the jets at the south pole, showing features as small as 8 metres across. Altogether, Cassini will make seven flybys of Enceladus during the extended mission.

Cassini has also observed an unexpectedly large stream of charged particles coming from the 1120-kilometre-wide moon Dione, which hints that it may power jets too. Cassini will fly by Dione during the extended mission to find out. It will also visit Rhea and the mini moon Helene.

Methane lakes

Mission scientists will continue peeling back the atmospheric haze that shrouds Saturn's largest moon, Titan, in mystery. Titan is slightly larger than the planet Mercury. Cassini has used radar to peer through the haze and map the moon's exotic surface, which appears to host lakes of liquid methane.

"We've found both dried and very likely liquid-filled lakes at the polar regions – who knows what else we're going to find," says Porco. Cassini will fly past Titan 26 more times during the extended mission, increasing the mapped area of its surface from 22% to 30%.

The spacecraft may also have the opportunity to beam back the most extraordinary images of Saturn's rings ever seen. On 11 August 2009, the rings will be aligned exactly edge-on to the Sun. Porco says this should allow Cassini to see subtle features like corrugations in the rings more clearly than ever before.

The Cassini team hopes the spacecraft will operate for several years even after the extended mission, if it remains healthy. When it eventually runs out of fuel, there is talk of intentionally flying the probe into Saturn's atmosphere, where it could make some unique measurements before burning up.

Cassini: Mission to Saturn - Learn more in our continually updated special report.

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