The 3-body Problem: a study shows that an inhabited exoplanet like in Liu Cixin's trilogy would be improbable

What bad news for Trisolarians! In Liu Cixin's excellent novels and the series that were adapted from it, a civilization develops on an exoplanet in the triple star system Alpha Centauri. But because of the chaotic orbits generated by their three suns, these extraterrestrials are forced to come and colonize the Earth.

Do civilizations observe magnificent triple sunrises somewhere in the Milky Way? Nothing prohibits it. However, astronomers found that of 26 triple star systems housing exoplanets, the majority of them were much younger than the average age of stars in the Galaxy. This means that in a fairly short (galactic) time, their planets are ejected due to gravitational interactions and the instability of their orbits.

Indeed, when a cloud of dust and gas, called nebulacollapses under its own weight to give birth to one or more stars, it also gives birth to planets with the residual material. However, the orbits of the planets will be more or less stable depending on the different massive components of the system, a bit like a class with several turbulent students will be more complicated to manage than another with only one or two strong heads. We already knew that the majority of orbits generated by a three-body system are unstable over time and strongly dependent on what physicists call their initial conditions.

Cuntz and Patel, the authors of the study published on arXivtherefore wanted to examine more precisely the systems of this type that we know. First observation: these triple systems rarely host several exoplanets, and when they do, it is often only one. First clue!

Once we establish the age of the stars, we notice that about half are younger than our Sun and 75% are younger than the average age of stars in our galactic neighborhood. Another important indicator: with the notable exception of the Kepler-444 system and its venerable 11 billion years, old triple stars have no or no more planets around them! It is as if, from a certain age, star parents said to their planet children: “Okay, you're grown up, go visit the vast Galaxy now!”

If the slow evolution of terrestrial life is a rule, then civilizations observing triple sunrises are rare in the Galaxy!

In the end, of the 26 triple systems with exoplanets, the authors obtained an average age of around 3 billion years. The Earth has blown out 4.5 billion candles and animal life as we know it has only existed for around 450 million years. The lineage Homo to which Humanity belongs, capable of manufacturing rockets and inventing constellations by wondering under the starry sky, has existed for only 2 to 3 million years. Life takes a rather long time to evolve on Earth, which is a planet in a very stable system. Of course, during brief and violent natural disasters, natural selection can act more quickly… So? Are the Trisolarians eyeing our blue planet?

As a gift for our readers, here is the Chinese version of the serial adaptation of 3 body problem. You can get French subtitles by setting to Automatic translation and choosing French: