But what is exciting scientists is that they are increasingly confident that there is life among the sediment at the bottom of that water ocean.
New pictures of the surface of Europa, which is slightly smaller than Earth's moon, were taken by the Galileo spacecraft and released yesterday by the US space agency Nasa. They back up the theory that undersea volcanic activity is going on near the moon's core - while separate research published today in the journal Science suggests that undersea volcanic vents provide ideal conditions for chemical reactions leading to organic life.
At a Nasa news conference yesterday John Delaney, of the University of Washington, said: "I am sure there's life out there." Richard Terrile, of Nasa's Jet Propulsion Laboratory, said added that he thinks there is organic matter at the bottom of Europa's ocean. "On Earth, these same ingredients gave rise to life."
While the scientists caution-ed that they have no direct evidence that there are living organisms at the bottom of Europa's ocean, they called the latest photos - which show a surface composed of ice "rafts" comparable to icebergs on Earth, and smaller meteor impact craters than a rock-solid surface would have - a "smoking gun".
The implication is that Europa may have a thin ice crust covering either liquid water or slush. "We're intrigued by those blocks of ice, which are like those seen on Earth's polar seas during springtime thaws," said Ronald Greeley, of Arizona State University, who is working with the Nasa team. "Their size and geometry leads us to believe there was a thin icy layer over water or slush, and that some motion caused these crustal plates to break up."
Other research published today in Science demonstrates that undersea volcanic vents, which are often too far down in the ocean to receive sunlight, do provide the chemical conditions needed to form molecules which are precursors of life. Other research has also shown that life can arise in environments which are completely cut off from sunlight.
This means that lack of sunlight at the bottom of Europa's ocean would not prevent life arising in the right conditions. Europa is slightly smaller than the Earth's moon, but has an ice crust. Calculations of its orbit around Jupiter have suggested that its solid core is warmed by tidal forces - which could in turn lead to volcanic activity near the core, and form an ocean of melted ice beneath the crust.
The solar flare thrown off from the Sun on Monday will not seriously affect the Earth, scientists said yesterday. Fears that the cloud of charged particles could disrupt power grids and satellites receded following new observations of the flare, expected to reach us today, after travelling through space at up to three million miles per hour.Reuse content