It is regarded as the most probable place in the solar system to host alien life.
And now Jupiter’s moon Europa has been found to have tectonic activity like Earth.
It is also the first time this specific type of geological activity has been observed in the solar system other than on our planet.
Scientists have found evidence of plate tectonics on Jupiter's moon Europa (pictured) – the first sign of this geologic activity on a solar system world other than Earth, raising hopes that life could one day be found there
Less than a year ago, scientists discovered plumes of water vapour erupting from Jupiter's moon’s south polar region, so it may be possible for a robotic probe to sample Europa’s liquid water at a distance without landing on it.
The latest find appears to solve a puzzle that has perplexed planetary scientists for years.
Until now, researchers have had visual evidence of Europa’s icy crust expanding, but they could never find areas where the old crust was being destroyed to make room for the new.
Examining images of the moon taken by Nasa’s Galileo orbiter in the early 2000s, planetary geologists Simon Kattenhorn of the University of Idaho and Louise Prockter of the Johns Hopkins University Applied Physics Laboratory in Maryland, discovered some unusual geological boundaries.
The surface of Europa is slightly smaller than the Earth’s moon and is riddled with cracks and ridges. Blocks on the surface are known to have shifted in the same way blocks on either side of the San Andreas Fault move past each other on Earth.
The surface of Europa is slightly smaller than the Earth’s moon and is riddled with cracks and ridges. Blocks on the surface are known to have shifted in the same way blocks on either side of the San Andreas Fault move past each other on Earth
JUPITER'S MOON EUROPA: THE 'MOST LIKELY PLACE IN THE SOLAR SYSTEM TO SUPPORT LIFE'
Europa is the sixth closest moon to Jupiter and the smallest of the four Galilean satellites that belong to the planet.
It was discovered by Galileo Galilei in January 1610 and is named after a Phoenician noblewoman in Greek mythology who was courted by Zeus and became the Queen of Crete.
Europa orbits Jupiter in around three-and-a-half days with an orbital radius of 670,900km.
It is slightly smaller than the Earth's moon, but at 3,100km in diameter it is the sixth largest moon and 15th largest object in the entire solar system.
It is likely to have an outer layer of water, some 100km thick.
The outer layer of the water is believed to be frozen with a liquid ocean underneath.
The moon has plate tectonics like on Earth.
It is one of the smoothest objects in the solar system with few craters on its surface, which is tectonically active and relatively young.
Many parts of Europa’s surface show evidence of extension, where wide bands - up to tens of miles wide - formed as the surface ripped apart, and fresh icy material from the underlying shell moved into the newly created gap, a process akin to terrestrial seafloor spreading, according to the study published in the journal Nature Geoscience.
‘We have been puzzled for years as to how all this new terrain could be formed, but we couldn’t figure out how it was accommodated. We finally think we’ve found the answer,’ Dr Prockter said.
Scientists studying Europa often reconstruct the moon’s blocks into their original configuration to get a picture of what the surface looked like before disruption occurred.
It was when they were rearranging the terrain that the two experts discovered that more than 12,000 square miles (nearly 20,000 square km) of the surface in the moon’s high northern latitudes was missing.
Further evidence suggested that the missing terrain had moved under a second surface plate - a scenario commonly seen on Earth at plate-tectonic boundaries.
The two scientists said that ice volcanoes on the overriding plate possibly formed through melting and absorption of the slab as it moved below the surface, while a lack of mountains at the subduction zone, implies that material was pushed into the interior rather than crumpled up as the two plates mashed against each other.
The surface of Europa is slightly smaller than the Earth's moon and is riddled with cracks and ridges. Blocks on the surface are known to have shifted in the same way blocks on either side of the San Andreas Fault (pictured in San Luis Obispo in California) move past each other on Earth
Less than a year ago, scientists discovered plumes of water vapour erupting from the moon’s south polar region (illustrated), so it may be possible for a robotic probe to sample Europa’s liquid water at a distance without landing on it
They believe the subducted slab has been absorbed into Europa's ice shell – which may be up to 20 miles (about 30 kilometers) thick - rather than diving through it into the moon’s underlying ocean.
Europa’s surface is considered to be relatively young at between 40 and 90 millions of years old, which can perhaps now be explained by plate tectonics as older material was destroyed.
Scientists have previously seen evidence of material moving up from under the shell, but until now, no mechanism had been found for moving material back into the shell, and possibly into the large ocean below the ice.
‘Europa may be more Earthlike than we imagined if it has a global plate tectonic system,’ Dr Kattenhorn said.
He told Space.com: ‘Earth may not be alone. There may be another body out there that has plate tectonics. And not only that, it's ice!’
There have been various proposals to explore Europa over the years, such as the Cryobot (pictured) which would be taken underground by a larger drill before it was then released into the ocean, searching for signs of past or present alien life
‘Not only does this discovery make it one of the most geologically interesting bodies in the solar system, it also implies two-way communication between the exterior and interior – a way to move material from the surface into the subsurface – a process which has significant implications for Europa’s potential as a habitable world.’
Some scientists said that plate tectonics were essential to how life evolved on Earth. The theory goes that tectonics replenished nutrients and helped to stabilise the Earth’s climate.
Jupiter's moon’s shell is thought to be 12 to 19 miles (20 to 30 kilometres) thick to subducting plates probably plunge a mile below the surface, so it is unlikely that nutrients from the surface are carried down to the ocean quickly. But Dr Kattenhorn said that this could possibly happen over time.
NASA SETS ASIDE $25 MILLION TO PROBE EUROPA
Nasa has set aside £14.6 million ($25 million) to design probes that could reveal whether Europa is habitable.
In July, the agency asked scientists to come forward with potential experiments for a Europa probe that could be launched in the 2020s and arrive at the icy satellite within three years of take-off.
It said that next year, about 20 proposals will be chosen to receive shares of the £14.6 million ($25 million) for further study.
The mission is designed to characterise the extent of Europa's ocean and its relation to the deeper interior.
It will also look at the ice shell and determine global surface, compositions and chemistry, especially related to whether life could survive in that environment.
Previous scientific findings point to the existence of a liquid water ocean located under the moon's icy crust.
This ocean covers Europa entirely and contains more liquid water than all of Earth's oceans combined.
Although Europa and Jupiter's other moons have been visited by other spacecraft, they were each limited to a single distant flyby of these satellites.
Nasa’s Galileo spacecraft, launched in 1989 by the space shuttle, was the only mission to make repeated visits to Europa, passing close by the moon fewer than a dozen times.
In December 2013, Nasa’s Hubble Space Telescope observed water vapour above the moon's frigid south polar region.
This provided the first strong evidence of water plumes erupting off the moon's surface, and a spacecraft could even be designed to fly through the plumes to make measurements of the composition of the underground ocean.