Although the existence of roving exoplanets, which float in interstellar space without orbiting a star, has been known for several decades, the James Webb Space Telescope recently identified more than 500 of them, leading to renewed interest in these lone stars. According to a new study, our solar system may have acquired some of it during its 4.5 billion years of existence. Based on their simulations, scientists estimate that a Mars-sized planet could orbit our Sun at a distance of approximately 1,400 AU… even though it formed around another star!
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[EN VIDÉO] The ninth planet in the solar system? Astronomers are convinced of this. It is possible that there is a ninth planet at the far end of the Earth…
Wandering planets – or nomads, also called “free planetary mass objects” – are objects that have planetary mass, but do not orbit a star. Therefore, they travel freely in interstellar space and are therefore not bound by the gravity of another star. This is also what makes them so difficult to spot: they appear very dark in the planetarium, because there is no star to illuminate them. Therefore, commonly used exoplanet detection methods, such as the transit method (which consists of observing a periodic change in the brightness of a star, indicating the passage of an object in front of it), cannot be applied to detect exoplanets. Nomadic planets. Thus, rare roving planets have been observed using the gravitational lensing method, or by direct imaging when they are massive and hot enough. A recent study published in the journal arksifFor example, more than 500 roving planets have been identified, discovered using data collected by the James Webb Space Telescope. Astronomers estimate the number of nomadic planets in our galaxy alone at several billion, and some suggest they may be even more numerous than the “classical” planets orbiting a star.
Noticeable interest in these orphan planets
These planets are of great interest to scientists, because of their number: if they are indeed more numerous than the planets orbiting a star, then the search for habitable worlds, where life could develop, should include them. According to astronomers, some of them can actually provide temperature conditions that allow water to exist in a liquid state. On the other hand, they must have enough geological activity to produce the required amount of heat, and an atmosphere dense enough to produce global warming, preventing the heat produced by the planet from escaping into space. But scientists also want to know more about these wandering planets in order to better understand how planetary systems form: If they are byproducts of the planetary system formation process, studying them could help shed light on how planetary systems like ours emerge.
This animation shows a wandering planet, drifting alone through interstellar space. © NASA, JPL-Caltech, R. Hurt (Caltech-IPAC)
Scientists have not yet been able to decide on the processes that lead to the formation of a wandering planet, and generally vacillate between two hypotheses. The first suggests that these planets could form in the same way as stars, after the gravitational collapse of a molecular cloud; According to this idea, only the amount of material available would prevent a planet from becoming a star. This hypothesis tends to scientists use the term “brown dwarf” to refer to these nomadic planets. The second hypothesis suggests that rovers will form inside a protoplanetary disk, like other “classical” planets, before being ejected from it. According to this idea, it is also possible that our solar system contains more planets today than it would have been ejected at the beginning of its history. Either way, these wandering planets can produce interactions with stars or planets they may encounter during their journey through interstellar space. Although this phenomenon has not yet been observed, astronomers point to the possibility of capturing wandering planets within planetary systems that they may encounter.
A wandering planet captured by our solar system?
The motivation behind this idea is that a researcher at Princeton University wondered whether our solar system could have captured such planets during its 4.5 billion years of existence. He presents his work in the magazine Astrophysical Journal Letters. According to hundreds of millions of numerical simulations performed, it is possible that our solar system has captured one or even several wandering planets. The author indicates, according to the simulations he conducted, that one or more of the rocky planets with a mass greater than the mass of Mars could have fallen into the grip of our sun's gravity, and settled in an orbit ranging between 600 and 3,500 astronomical units from the sun. (For comparison, the distance between Earth and the Sun is one astronomical unit, and Pluto orbits about 39 astronomical units from our star.)
If the existence of wandering planets in our solar system is still theoretical, this new work tends to show that it is still very likely. Studying such a planet could be a veritable goldmine for scientists seeking to better understand planetary formation processes (whatever hypothesis is considered). Additionally, if our solar system has a rocky planet, studying its surface could help us learn more about the habitability of terrestrial exoplanets in general. Until such a planet is discovered in our solar system, the author suggests future studies to investigate the processes that would allow a wandering planet to be captured in a star system.
