Life may swim within distant moons

Oceans of water beneath the icy surfaces of distant moons may be far more common in the outer Solar System than had been thought, according to new calculations.

Some, in theory, could harbour life, claim scientists.

Until now it was believed that oceans might be found under the icy crust of Jupiter's moons Ganymede, Europa and Callisto.

But new calculations, by Christopher England of Nasa's Jet Propulsion Laboratory (JPL), to be presented at a major astronomy conference, suggest that this may be the case on other moons, such as Titan - which orbits Saturn - and Neptune's large moon Triton.

Even Varuna, the largest so-called Trans-Neptunian object that orbits the Sun in the cold outer reaches of the Solar System, may posses an ocean, they say.

Water water everywhere

For many years Jupiter's ice-encrusted moon Europa has been suspected of harbouring an ocean of water trapped beneath its icy surface.

The evidence for the ocean is threefold - coming from magnetic effects observed by the passing Galileo spacecraft, surface features that suggest there could be an ocean beneath them and calculations of heat flow from Europa's interior.

The possible presence of an ocean hand the possibility of energy sources on the ocean floor, such as hydrothermal vents, has led to widespread speculation about the possibility of life developing in such an environment.

In 2000 the Galileo spacecraft increased the number of Jupiter's moons that could have subsurface oceans to three when magnetic measurements taken as the probe passed Ganymede and Callisto suggested the presence of salty water beneath about 170 kilometres (105 miles) of ice.

In a new study Christopher England of JPL has developed a mathematical model of the icy and rocky world of the outer Solar System.

Making reasonable assumptions about the amount of heat-generating radioactivity in the cores of the moons of Jupiter, Saturn, Uranus, Neptune and Pluto, Dr England is able to determine if enough energy exists to melt a layer of ice beneath the surface to form an enclosed ocean.

Life everywhere?

The calculations confirm that Jupiter's Ganymede, the Solar System's largest moon, as well as Callisto and Europa could well all have substantial subsurface oceans.

Oceans could also be found beneath the surfaces of Saturn's major moon Titan as well as its smaller moon, Rhea.

Titania and Oberon orbiting Uranus could have oceans as could Triton, Neptune's major moon. Even Pluto qualifies.

Intriguingly, some of the larger of the recently discovered Trans-Neptunian objects that circle the Sun beyond Neptune and Pluto may also generate enough internal heat to form a subsurface ocean. Varuna, discovered in 2001, is the prime candidate.

Before this study Europa's ocean was considered to be a prime location for the possibility of life. With so many possible places where liquid water could be present in a confined place exposed to important chemicals and energy sources, scientists will wonder if life could develop elsewhere in our Solar System.