Page last updated at 17:47 GMT, Wednesday, 13 August 2008 18:47 UK

Probe gets close up to Enceladus

Enceladus (image taken at a distance of about 2,600km)
The tiger stripe named Cairo is the deep feature at bottom right

The Cassini spacecraft has returned some remarkable new close-up images of the Saturnian moon Enceladus.

They were captured during a flyby on 11 August, with the probe passing above the icy terrain at a distance of just 50km at closest approach.

The pictures show previously unseen detail in the so-called tiger stripes that mark the south pole of Enceladus.

These cracks run across a "hot-spot" region that is hurling plumes of ice particles into space.

Scientists are intrigued by what might be driving this activity; and some have suggested the mechanisms involved could be sufficient to maintain a mass of liquid water below the moon's surface.

The flyby follows a similar close pass made in March, although on that occasion Cassini was turned to give the prime view to its Ion and Neutral Mass Spectrometer (INMS) and its Cosmic Dust Analyzer (CDA) - to allow them to "taste" the plumes.

Closer still

On this occasion, Cassini gave primacy to its cameras - its Imaging Science Subsystem - and the rest of its optical remote sensing instruments.

With the probe moving across the surface of Enceladus at 18 km/sec (about 40,000 mph), obtaining good pictures proved to be quite a challenge for the imaging team.

"The challenge is equivalent to trying to capture a sharp, unsmeared picture of a roadside billboard about a mile away with a 2,000mm telephoto lens held out the window of a car moving at 50mph," they reported on their blog.

Two more Enceladus flybys are planned for October, the first of which will go even closer - to an astonishing 25km from the surface.

Enceladus measures about 500km in diameter, just one-seventh the diameter of Earth's moon.

Cassini's manoeuvres are being commanded from Earth, at distance of more than one billion km.

The Cassini-Huygens mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (ASI).

An artist's impression of a sunset on Enceladus. The plumes have been one of the great discoveries of the Cassini mission

Saturn moon 'once had ocean'
14 Mar 08 |  Science/Nature
Cassini makes audacious flyby
11 Mar 08 |  Science/Nature
Sodium issue clouds Enceladus
16 Dec 07 |  Science/Nature
Moon jets pinned on 'tiger stripes'
11 Oct 07 |  Science/Nature

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