The European Space Agency (Esa) is preparing to launch a satellite on the planet Jupiter, one of the organization’s most ambitious missions.

The satellite will leave Earth on Thursday for an eight-year journey to reach the giant planet’s major moons.

There is good evidence that these icy worlds – Callisto, Europa and Ganymede – contain oceans of liquid water at depth.

The Esa mission aims to establish whether the moons might also have the conditions necessary to sustain life.

The project is known as Jupiter Icy Moons Explorer, or Juice for short.

Juice isn’t looking to detect life – it won’t return images of alien fish. But it could help determine whether conditions in the moons’ hidden oceans have at least a chance to support simple microbial organisms.

It’s not a crazy idea, says Professor Carole Mundell, scientific director at Esa.

“In every extreme environment on Earth, whether it’s high acidity, high radioactivity, low or high temperature – we find microbial life in one form or another.” she told BBC News.

“If you look at the (volcanic) vents at the bottom of Earth’s oceans, they even look like alien worlds. There’s no reason why this microbial life can’t exist elsewhere, if we have conditions similar. And those are the conditions that we want to study with Juice.”

The €1.6bn (£1.4bn; $1.7bn) mission is set to launch on an Ariane-5 rocket from Kourou, French Guiana at 09.15am local time (1.15pm BST) .

The Ariane doesn’t have the energy to send Juice directly to Jupiter, certainly not in a useful time frame.

Instead, it 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.

Arrival in the Jovian system is scheduled for July 2031.

Juice will make 35 close passes of the moons – sometimes approaching within 400 km of their surface – before orbiting Ganymede.

The spacecraft carries a total of 10 instruments. There are various cameras, particle detectors, radar to map the features of the subsoil; there’s even lidar, which is used to make 3D maps of the surface terrain.

But it is the magnetometer provided by the UK that could provide some of the most influential data. The experiment built by Imperial College London will tell us about the properties of the hidden oceans of the moons. And in Ganymede, in particular, the information should be quite detailed.

“We will know the depth of the ocean, its salt content, the depth of the crust above the ocean and whether the ocean is in contact with the rocky mantle,” explained lead researcher Professor Michele Dougherty. Imperial’s magnetometer.

“Thus, we will understand the interior structure of the moon, and from observations of other instruments looking at the surface, we will be able to determine if there is organic matter on this surface.”

The Earth has taught us that life needs four essential inputs: liquid water, some kind of nutrient, a source of energy, and time – a long period of stability in which biology can gain a foothold and establish itself. .

We have long considered Mars to be the most likely candidate to host extraterrestrial life, if not today, then at least in its distant past.

But for astrobiologists – scientists who study the possibility of life elsewhere in the Universe – the ice-covered moons of Jupiter and also Saturn are really starting to pique their interest.

These worlds may be in the cold, outer reaches of the solar system, far from the Sun, but they might just be able to satisfy all four inputs – even for an energy supply. It is not the light and heat of a star, but the constant gravitational pressure and pull that the giant planets exert on the moons.

It is this bending that provides the means to hold water in liquid form and could also result in the type of volcanic vent systems on the ocean floors mentioned by Professor Mundell and which some scientists believe may have been at the bottom. origin of life on Earth.

“If I was a bettor, I would probably bet that Europa has living life, which exists today,” says Professor Lewis Dartnell, an astrobiologist at the University of Westminster. “The odds of that being much higher than finding extant (living) life on Mars today.”

The United States will launch its companion mission, known as Clipper, next year. It will focus on Europa, making 50 flybys, some as low as 25 km.

The close pass of a planetary destination is usually followed by a subsequent spacecraft going into orbit and then another mission attempting to land.

This is how exploration has progressed on Mars, where we are about to take the next step – that of trying to bring material back to Earth to study in the laboratory.

Investigations of Jupiter’s and Saturn’s moons aren’t as far along in the sequence, but it’s possible to envision projects later this century that could land on these fascinating outer solar system bodies and seek to breach their icy crusts. and sample the waters below.

“If we find evidence of life on the moons of Saturn or Jupiter, then it would almost certainly be of independent origin,” says Astronomer Royal Professor Sir Martin Rees.

“It would then carry a momentous message that life – if it had started twice, independently, in our solar system – cannot be a rare happenstance, and almost certainly exists in a billion places in our galaxy, and that transforms completely the way we look at the sky.”