Jupiter's moon, Europa, has been described as one of the most likely places in the solar system for life to thrive. 

The moon, which lies 500 million miles from the sun, has an ocean lying beneath its surface that could host microbes.

Now, Nasa says it has taken a small step to sending a robotic landing craft and underwater robots to Europa to search for life.  In a report this week, the space agency revealed its three goals for the upcoming search for life.

It wrote: 'The primary goal is to search for evidence of life on Europa.

'The other goals are to assess the habitability of Europa by directly analysing material from the surface, and to characterise the surface and subsurface to support future robotic exploration of Europa and its ocean.' 

Roughly the size of Earth's moon, Europa is structurally like a liquor-filled chocolate, with a ocean that could be 62 miles (100 kilometres) deep. 

Scientists have long thought that the sea is one of the best potential alien incubators in our solar system.

A Europa Lander would be the first Nasa mission dedicated to the search for aliens since the Viking Mars spacecraft in the 1970s. 

Nasa believes any alien life on Europa  will likely be in the form of microbial cells. 

'The science return possible from the model payload is such that if life is present in Europa's ice at a level comparable to one of the most extreme and desolate of environments on Earth (Lake Vostok ice) then this mission could detect life in Europa's icy surface,' it said. 

'The initial search for signs of life on Europa will largely take the form of a biochemical search.'  

Europa has no atmosphere so they would not be able to land the robot using heat shields or parachutes. 

The lander could work for roughly 20 days before it ran out of batteries, and the earliest touchdown date is expected to be April of 2031. 

If the lander reconnaissance mission is successful, Nasa may send underwater robots to explore the oceans beneath the surface.   

'Depending on the exact mission concept under consideration, autonomous underwater vehicles exploring ocean worlds will need to operate autonomously for days to months,' Steve Chien of NASA's Jet Propulsion Laboratory told Astrowatch.net. 

'Within this time frame, they must manage their own resources, explore a largely unknown environment, including navigating to and from a single point of insertion which also serves as a communications link to the outside world', he said.  

Nasa will be working closely with engineers to design a system that will allow the robot to land on the surface. 

The space agency is currently planning a flyby mission of Europa that will launch in the early 2020s. 

The flyby is expected to help scientists map its composition and work out the make up of its icy shell and ocean.

The space agency is now planning two meetings to discuss the Europa Lander report, which will take place on 19 March and 23 April.