The outer solar system is like the last frontier of the wilderness. It’s so far from the Sun that our telescopes can’t easily see what’s there; One can only guess what strange objects are hiding in the far corners of the planetary disk.

We know that there is an area of ​​small icy rocks beyond the orbit of Neptune. This is the Kuiper belt, where the dwarf planets Pluto, Eris and Haumea are located. Far beyond this is the hypothetical Oort Cloud, a vast spherical area of ​​small rocks surrounding the entire Solar System, whose actual size is unknown.

The Solar System’s long-period comets are believed to originate from here; But what else could be hiding there? One exciting possibility is the existence of planets; the existence of not only ancient planets but also planets of alien stars.

Theoretical astrophysicist Amir Siraj of Princeton University has determined how many alien planets may now be hidden from our view. According to his calculations on a purely mathematical level, there may be 1.2 planets with a mass greater than Mars; It has a mass comparable to the mass of Mars, 2.7; and 5.2, which has a mass comparable to that of Mercury.

These are just educated guesses based on other informed guesses, but the idea that there could be a single secret world drifting from a distant star is absolutely fascinating.

This question arose after the discovery of free-floating or roving planets, first published in 2000. These are planets that have broken away from their stars and left their home systems to wander the galaxy. It is believed that gravitational interaction creates the necessary instability quite easily, causing a bunch of planets to move rapidly through space.

It’s unclear how common this phenomenon is, but we’re getting better at spotting these solitary individuals, which means abundance estimates are becoming more accurate.

Even more interesting is the idea that these planets will not necessarily remain free. If they pass too close to the star, they will be captured by gravity. We know this can happen on a smaller scale; Jupiter looks like a rock-stealing space bandit.

Siraj wanted to know the probability of this happening to Sun. So he started by estimating the number of stray planets in the Milky Way and estimating the percentage of stars likely to be captured by stray planets. He used this information to calculate the probability that these planets would pass close enough to the Solar System to be captured by the Sun’s gravity.

Their calculations showed that there was a very high probability of a planet hanging out in the cold and dark, somewhere between the mass of Mercury and Earth.

“Based on a simple theoretical argument, we show that captured terrestrial planets probably exist in the outer solar system,” he writes in his paper.

“Future studies should include simulations that look more closely at the capture and eclipse of free-floating planets as well as planets bound to other stars. Additionally, simulations may shed light on probability distributions for captured planets’ orbital plane and positions in the sky.” “Future studies should also examine other observational tests for the existence of captured planets.”

He adds that if one were in a good enough position in the sky, we could detect it at the Vera K. Rubin Observatory, currently under construction in Chile and expected to begin scientific studies in 2025.