A planet floating in space far from any star appears to be the least likely place for life to emerge. But if such a planet had a moon, with the right orbit and atmosphere, it could provide conditions suitable for life for more than a billion years.
Giulia Rocetti, a doctoral student at the European Southern Observatory, explained how this could be achieved Thursday at a planetary symposium at the European Research Center Estec in Noordwijk.
Although only about 100 of these single planets have been observed, astronomers suspect there are at least as many of them as there are stars. These planets have been expelled from their solar system after the gravitational pull of another planet or passing star. And just like the regular planets in the solar system, they can have moons.
On such a moon, according to Chilean astronomer Patricio Javier Avila in 2021, it can be unexpectedly warm. If its orbit is not perfectly circular, but an ellipse, then the tidal movement of the planet is constantly deforming the rocks that make up the moon, generating friction and, consequently, heat. Planetary scientists see the same thing happening closer to home, with the moons of Jupiter and Saturn.
If such a moon also had sufficiently dense carbon dioxide2The atmosphere – so with a strong greenhouse effect – can get warm enough for water to become liquid. And water can get there, thanks to chemical reactions, which are caused by particles of cosmic rays colliding with particles of the atmosphere.
The heat tap is also closed again
This already satisfies an important condition for the origin of life. Roccetti went one step further. She ran this entire scenario with computer models. In the beginning, you let a small solar system with three planets—the size of Jupiter—evolve until the planet shrank. Then I calculated how many times the moon of such a planet – the size of Earth – remained attached to it. Then I followed them afterwards to see if the condition that Avila had calculated occurred, and above all: how long it would last. Because the heat of friction on the moon is extracted from the movement of the moon around the planet. This movement becomes more and more of a circle, and this slowly closes the heat tap.
“There could be many places in the universe that seem suitable for the emergence of life,” says Roccetti. “What we’re looking for are places where these conditions can persist for hundreds of millions or even billions of years.”
I concluded that an orphan planet’s moon could meet this requirement in her studieswhich was also published this week in International Journal of Astrobiology.
Long molecules are the beginning of life
In her calculations, it would have stayed warm enough for at most 52 million years if such a moon had an atmosphere as dense as Earth’s. With an atmosphere 10 times denser, it is already 276 million years, and 100 times it is 1.6 billion years. That’s fine, it’s the kind of atmosphere Venus has.
Whether life could easily arise on a dark but warmer moon than on a planet lit by a star, no one knows yet. But Roccetti sees the benefits. “There is water, but not much. All sorts of places are likely to experience alternating periods of dryness and wetness. This is conducive to the formation of the long molecules that life must begin with. A star produces solar flares as well as heat. They can steal a planet that would otherwise be just the distance.” suitable to be suitable for life, from its atmosphere.” Lonely Planet Moon is not affected by this.
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