The European Space Agency will make another attempt on Friday to launch its Jupiter Icy Moons Explorer (Juice).

Thursday’s bid was stymied by concerns about lightning over the Kourou spaceport in French Guiana.

Juice is sent to the largest planet in the solar system to study its major moons – Callisto, Ganymede and Europa – all of which are believed to hold vast reservoirs of liquid water.

Scientists are intrigued whether moons could also harbor life.

It may sound fancy. Jupiter sits in the cold, outer reaches of the solar system, far from the Sun and receiving only one-twenty-fifth of the light falling on Earth.

But the gravitational squeeze the gas giant planet exerts on its moons means they potentially have the energy and heat to power simple ecosystems – much like those that exist around volcanic vents on Earth’s ocean floor.

“In the case of Europa, there is thought to be a deep ocean, possibly 100 km deep, beneath its ice crust,” said mission scientist Professor Emma Bunce of the University. from Leicester, UK.

“That ocean depth is 10 times the deepest ocean on Earth, and the ocean is in contact, we think, with a rocky bottom. So that provides a scenario where there’s mixing and interesting chemistry,” the researcher told the BBC. News.

Liftoff of the six-tonne Juice spacecraft is scheduled for 09:14 a.m. local time in Kourou (1:14 p.m. BST).

The Ariane rocket that will take the mission to the skies has an instantaneous launch window, which means it must take off in the second required by the computers.

The precision will help keep the mission on track as it heads on the long journey to Jupiter.

Ariane doesn’t have the clout to send Juice straight to her destination, at least not in a timely manner.

Instead, the rocket will send the spacecraft on a path around the inner solar system. A series of flybys of Venus and Earth will then gravitationally launch the mission to its intended destination.

It is a journey of 6.6 billion km that lasts 8.5 years. Arrival in the Jovian system is scheduled for July 2031.

The ice-covered moons Callisto, Ganymede and Europa were discovered by Italian astronomer Galileo Galilei in 1610, using the recently invented telescope. He could see them as little dots revolving around Jupiter. (He could also see a fourth body that we now know as Io, a much smaller world covered in volcanoes).

The ice trio has a diameter of 4,800 km to 5,300 km. To put that into context, Earth’s natural satellite is about 3,500 km in diameter.

Juice will study the moons remotely. That is, it will fly over their surfaces; it won’t land. Ganymede – the largest moon in the solar system – is the satellite’s ultimate target. It will end its tour by orbiting this world in 2034.

The radar will be used to see into the moons; lidar, a laser measuring device, will be used to create 3D maps of their surfaces; magnetometers will explore their complex electrical and magnetic environments; and other sensors will collect data on the swirling particles that surround the moons. The cameras, of course, will return countless images.

Juice won’t be looking for particular “biomarkers” or trying to find alien fish in the depths of the ocean.

Its task is to gather more information about potential habitability so that subsequent missions can more directly address the question of life.

Scientists are already considering how they could place landers on one of Jupiter’s frozen moons to drill through its crust to the water below.

In terrestrial Antarctica, researchers are using heat to drill hundreds of meters through the ice cap to deploy submersibles in places where the local ocean is frozen.

It’s hard work and would be an even bigger task on a Jovian moon where the ice crust could be tens of kilometers thick.

Juice will not be alone in his work.

The American space agency Nasa sends its own satellite called Clipper.

Although he will leave Earth after Juice, next year he is expected to arrive just before his European sibling. It has the advantage of a more powerful launch rocket.

Clipper will focus its investigations on Europa, but will do much the same work.

“There is great complementarity and the teams are very keen to collaborate,” said Professor Carole Mundell, scientific director of the European Space Agency.

“Certainly there will be a wealth of data. But, first, we need to make sure our missions get to Jupiter and operate safely,” she told BBC News.