With just two days before it nose-dives into Saturn and burns up in the giant planet's atmosphere, Nasa's Cassini spacecraft is being given something of a hero's farewell by the astronomy community and space fans everywhere.

In the final months of its 20 year journey - most of that mission time having been spent orbiting Saturn - the schoolbus-sized craft has treated scientists to incredible insights into the Solar System's second-largest planet.

With propellant running low, Nasa scientists are concerned that the probe might accidentally crash into one of Saturn's nearby moons, which could contaminate it with Earthling bacteria stuck to the spacecraft.

Instead, the spacecraft will be safely "disposed" in Saturn's atmosphere.

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The spinning vortex of Saturn's north polar storm has an eye measured at a staggering 2000km across. Photo / Nasa
The spinning vortex of Saturn's north polar storm has an eye measured at a staggering 2000km across. Photo / Nasa

"Cassini's spectacular finale is, in part, a tribute to its success," University of Auckland cosmologist Professor Richard Easther told the New Zealand Science Media Centre.

"All spacecraft carry stowaways: bacterial spores which can, remarkably, remain viable in the vacuum of space.

"And one of Cassini's many discoveries was that three of Saturn's moons appear to have oceans of water beneath their solid crusts."

Another University of Auckland physics lecturer, Dr Nick Rattenbury, said the images relayed back helped scientists understand that world and the forces that governed its extensive atmosphere - and its orbiting disk of ring material.

This near-infrared, color view from Cassini shows the sun glinting off Titan's north polar seas. Photo / Nasa, JPL-Caltech, Univ. Arizona, Univ. Idaho.
This near-infrared, color view from Cassini shows the sun glinting off Titan's north polar seas. Photo / Nasa, JPL-Caltech, Univ. Arizona, Univ. Idaho.

"Apart from the planet itself, the mission made sensational discoveries on the moons of Titan and Enceladus," Rattenbury said.

"We've long known that Titan has an extensive atmosphere, thick and opaque, hiding that moon's surface from us here on Earth.

"The Cassini mission revealed surface lakes and rivers on Titan's surface, the first clear evidence of a liquid present on the surface of a world other than our own Earth."

Cassini's Huygens probe descended into the thick atmosphere of Titan, recording and transmitting data as it descended and even after landing on the surface.

"Our new knowledge of these alien surface lakes and Titan's thick atmosphere adds vital fuel to the debate on how and where life could catch a hold on alien worlds.

This stunning false-colour view of Hyperion reveals crisp details across the strange, tumbling moon's surface. Photo / Nasa
This stunning false-colour view of Hyperion reveals crisp details across the strange, tumbling moon's surface. Photo / Nasa

"Enceladus, another moon of Saturn, had plumes of material jetting out into space.

The Cassini mission captured high-resolution images of these remarkable geyser-like jets, which contain water.

"To those of us interested in finding alien worlds on which life could emerge, water is considered as - almost certainly - the most likely medium in which life could emerge

"However, Cassini wasn't finished there, collecting evidence that in addition to water, there was a source of energy - methane - that could be used by life."

The wavemaker moon, Daphnis, is featured in this view, taken as NASA's Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn's rings on Jan. 16, 2017. Photo / Nasa
The wavemaker moon, Daphnis, is featured in this view, taken as NASA's Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn's rings on Jan. 16, 2017. Photo / Nasa

But leaving the spacecraft to wander unguided around the Saturnian system would have risked a collision with one of these moons, Easther explained.

"So, rather than let its microbial hitchhikers disembark onto a pristine world, Cassini will not 'go gentle into the good night' as its propellant runs low, but has been steered towards a fiery demise."

While Nasa had an undoubted ability to sell a story, in this case, the hype is not misplaced, Easther said.

Saturn had a key place in the evolving human understanding of the cosmos.

The most distant planet easily visible to the naked eye, Saturn once marked the apparent edge of our solar system.

A giant of a moon appears before a giant of a planet undergoing seasonal changes in this natural color view of Titan and Saturn from Nasa's Cassini spacecraft. Photo / Nasa
A giant of a moon appears before a giant of a planet undergoing seasonal changes in this natural color view of Titan and Saturn from Nasa's Cassini spacecraft. Photo / Nasa

"Its rings are visible through even the smallest of telescopes, and seeing them this way still takes your breath away," Easther said."Cassini has shown us Saturn with its rings and its moons up close and personal, with astonishing clarity and precision.

"The spacecraft and the team of scientists responsible for it have written themselves into the history books."

The F ring shepherd Pandora is captured here along with other well-known examples of how Saturn's moons shape the rings. Photo / Nasa
The F ring shepherd Pandora is captured here along with other well-known examples of how Saturn's moons shape the rings. Photo / Nasa

Otago Museum director Dr Ian Griffin saw the launch of Cassini in 1997, while working at a planetarium and observatory very close to Cape Canaveral.

"In my opinion, Cassini has done some amazing science, and it has transformed our understanding of the Saturnian system."