• Oceans have been detected on the moons Europa, Ganymede, Enceladus and Titan.

  • These oceans can reach enormous depths compared to terrestrial oceans.

  • They offer the potential for an extraterrestrial life form.

The presence of water in our solar system, in the form of vapor or ice, has long been demonstrated and communicated by scientists.

But did you know that there is also liquid water?

And even downright oceans?

The research carried out by the space expeditions Galileo, around Jupiter, and Cassini, around Saturn, have indeed made it possible to make great progress on the subject.

Christophe Sotin, professor at the Planetology and Geosciences Laboratory in Nantes, is holding a public conference on this topic this Thursday evening*.

Interview with this planetary scientist also renowned for having been scientific director for the exploration of the solar system in the service of NASA.


You explain that there are hidden oceans on the moons of Jupiter and Saturn.

What are we talking about exactly?

We are talking about oceans of liquid water covered by an envelope of ice of several kilometres, even several tens of kilometres.

They are invisible but they are there.

They are even much larger than the Earth's oceans.

They can be up to 100 kilometers thick, compared to the average depth of our terrestrial oceans which is about 3 kilometers.

On which moons are these oceans located?

They have been detected on Europa, a natural satellite of Jupiter, thanks to the Galileo mission which, from the end of the 1990s, detected induced magnetic fields there.

The best explanation for these induced magnetic fields, which are also found in the terrestrial oceans, is the presence of a deep salty ocean.

The same observation was made on Ganymede, Jupiter's moon and the largest moon in the solar system.

Oceans have also been detected on Enceladus, a small moon of Saturn, thanks to the Cassini mission which revealed the presence of geysers there.

This is a real surprise because we thought that Enceladus was only a ball of ice cream.

Finally, the other moon where the presence of oceans is corroborated, with different methods, is Titan, the largest moon of Saturn.

Are these oceans conducive to life?

Yes, completely.

This is called habitable territories.

They are habitable places for simple lifestyles.

Which does not mean that they are inhabited.

For Enceladus and Europa, there is a strong resemblance to the bottoms of the terrestrial oceans.

Could we imagine finding plants or animals there?

No.

We rather think of single-celled organisms: bacteria, microbes… The same first forms of life that were on Earth 4 billion years ago.


How to know more now?

Going to look!

There is the

Europa Clipper

mission which will be launched in 2024 by NASA for the study of Europe.

There is a European mission which will be interested in Ganymede.

There is also the

Dragonfly

mission to go to Titan in 2028. And a project to go and study Enceladus in more detail.

The discovery of the oceans has generated great interest in the planetary community.

It involves people from all disciplines, biology, organic chemistry, not necessarily astrophysicists.

Why are these discoveries so fascinating?

Because water is an essential ingredient for life.

And that there is a link between the existence of extraterrestrial life and the emergence of life on Earth, a question that has still not been resolved.

There is also the question of whether life is unique to Earth or whether it can develop on other planets.

This subject is indeed fascinating, I see it with my students or the public attending conferences.

Can we think that there would be other oceans elsewhere in the solar system?

Yes !

There is a lot of talk about an ocean inside Pluto, another inside Triton [Neptune's moon].

There is Callisto, a moon of Jupiter, where it also seems possible.

And there are oceans that arguably once existed inside Ceres, which is now a dwarf planet but was previously known as the largest asteroid between Mars and Jupiter.

There is still a lot of exploration to be done!

* At 7 p.m., this Thursday, at the Nantes Natural History Museum.

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