Moons around ‘rogue planets’ could sustain life – no solar system required


Rogue planets are the wanderers of the galaxy, wandering alone in interstellar space. Now, it turns out they could have companionship in the form of moons – and possibly even support the life that came with them.

New simulations show giant planets driven from their solar system could cling to nearly half of their moons during the ejection process and potentially maintain living conditions for billions of years.

The work, which will be published in the Monthly notices from the Royal Astronomical Society, suggests that life may be more prevalent in the galaxy than we thought, said astrophysicist and study co-author Jason Steffen of the University of Nevada in Las Vegas.

“Let’s say there’s one star in a million that ejects a planet that looks like Jupiter, with its conditions.

“It’s 300,000 rogue planets [in our galaxy] who could have life on their moons. “

That’s a conservative estimate, he added: “We think it’s closer to 1%, rather than one in a million.”

Seek life in probable places

When it comes to looking for life as we know it, it’s hard to get past the “Goldilocks Zone” of a solar system, a region around a star where it is neither too hot nor too hot. cold so that liquid water exists.

But in recent years, astrobiologists have turned their gaze to less intuitive targets: giant planets drift away into the frozen confines of a solar system – or rather their moons.

There, far from the heating rays of the sun, the water remains liquid thanks to the heat generated by friction, when a moon is deformed by the gravitational attraction of its planet, as well as that of the other moons.

We see this “tidal bending” in our solar system with Jupiter’s moons suite, Dr Steffen said.

The three innermost moons, Io, Europe and Ganymede, revolve around Jupiter in what is called a resonant frequency: in the time it takes Ganymede to orbit once, Europe orbit twice and Io does so. about four times.


When Europe is directly between Jupiter and Ganymede, for example, it is pulled in two directions.

But when Ganymede is on the other side of Jupiter, Europe pulls harder in one direction.

All of that regular stretching and squashing causes enough heat to build up inside Europe and, planetary scientists suspect, maintains a liquid ocean under its icy crust – an ingredient of life.

And with the relatively recent discovery of rogue planets – huge Jupiter-like gaseous objects that roam the galaxy, not attached to a star – Dr Steffen and his student Ian Rabago asked: could they also harbor and sustain life? on their moons?

The moons that remain when the planets are ejected

To find out if the moons could survive a planetary ejection – or if they would be ripped off their planet – Mr. Rabago and Dr. Steffen performed 77 simulations of a planetary system with three Jupiter-like gas giants, each with moons.

To their surprise, they saw that almost half of the moons had survived.

“My hunch was that it would be less than that, maybe 10 percent,” Dr Steffen said.

“I certainly didn’t expect to have so many systems capable of keeping moons.”

About 22% of the moons remained in the solar system, while the rest were blasted into space, free of any stars or planets.

Simulations show that about a quarter of ejected planets retain most or all of their moons.(Provided: University of Nevada, Las Vegas)

The most gratifying result, Dr Steffen said, was that the simulated lunar systems with the same orbital resonance as Io, Europa and Ganymede were among those that survived.

“You could take Jupiter, you could kick it out of the solar system by natural processes, and these resonant conditions, and the potential for life, can survive.”

Aditya Chopra, an astrobiologist at Australian National University who was not involved in the study, said life on a rogue planet’s moon would likely be much more difficult to survive than if it stayed in a solar system. .

“Even though Europa is so far away, the sun’s UV rays break down chemicals on its surface, which could be useful for life,” he said.

“Rogue planets don’t get a lot of photons.

“And in the solar system you have this constant influx of matter, like comets, but you don’t have so much with rogue planets.”

And while spotting rogue planets isn’t an easy task at the moment – let alone any life that might linger on their moons – there is an advantage.

“The great thing about rogue planets and their moons is that they can visit us,” Dr. Chopra said.

He pointed to ‘Oumuamua, a comet from interstellar space that passed through our solar system last year.

“Maybe in the future we will find one of these rogue planets approaching us and we can test some of these ideas.”


Arline J. Mercier

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