Saturn probe spies 'cheese' moon

Epimetheus orbits about 91,000km from the top of Saturn's clouds Enlarge Image

The international Cassini spacecraft has obtained the closest picture yet of Saturn's small moon Epimetheus.

At just 116km (72 miles) across, the satellite is slightly smaller than its companion moon, Janus, which orbits at much the same distance from Saturn.

Looking not unlike a large lump of cheese, Epimetheus sports many craters.

One large impact site featured in the new picture is known as Hilairea, and appears as a deep hole with a diameter of about 33km (21 miles). The Joint US-European-Italian space agency mission continues to chalk up new findings.

Earth clues

Recent observations have shown large hydrocarbons exist high up in the atmosphere of Saturn's largest moon, Titan.

On its most recent flyby on 16 April, the spacecraft's ion and neutral mass spectrometer was able to get a good look at the range of complex molecules that hang many tens of kilometres above the surface.

Hydrocarbons, containing as many as seven carbon atoms were observed, as well as nitrogen-containing hydrocarbons (nitriles).

Cassini continues to return exceptional views of Titan More details

Titan's atmosphere is composed primarily of nitrogen, followed by methane, the simplest hydrocarbon.

US space agency scientists said nitrogen and methane were expected to form complex hydrocarbons in a process induced by sunlight or energetic particles from Saturn's magnetosphere.

However, it was surprising, they added, to find the plethora of complex hydrocarbon molecules in the upper reaches of the atmosphere.

Titan is very cold, and complex hydrocarbons would be expected to condense and rain down to the surface, the researchers explained.

The moon with its thick atmosphere is a fascinating target for researchers. Its chemistry is believed to resemble that on Earth 4.6 billion years ago.

As such, it may tell scientists more about the kind of reactions that set the scene for the emergence of life on our planet.

Bright target

Mission scientists have also announced the discovery of dust particles around another of Saturn's moons, Enceladus.

The particles might indicate the existence of a dust cloud around the satellite, or they may have originated from Saturn's outermost ring, the E-ring, scientists report.

Certainly, researchers are of the belief that the existence and evolution of the E-ring is intimately tied up with Enceladus.

The moon is rapidly becoming a very interesting target for Cassini.

Enceladus: The target of a very close flyby (Nasa/JPL/SSI)

Already, the probe's magnetometer has revealed the presence of a very thin atmosphere.

Scientists and engineers are planning to revise the altitude of the next Enceladus flyby to get a closer look.

The 14 July encounter was to have been at an altitude of 1,000km (620 miles), but the mission team now plans to lower that altitude to about 175km (109 miles).

This would be Cassini's lowest-altitude flyby of any object during its nominal four-year tour.

Enceladus, which measures 500km (310 miles) in diameter, is the most reflective object in the Solar System, throwing back about 90% of the sunlight that hits it.

Scientists say it is possible the high reflectivity could result from continuous deposition of icy particles originating from volcanoes.

The $3.2bn Cassini-Huygens mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).