Besides the eight known major planets, many smaller bodies orbit our sun, including trillions of comets, millions of asteroids, and vast numbers of smaller meteoroids. Most are probably indigenous to our solar system. But astronomers wonder whether a few might be aliens—pieces of debris that came from somewhere else far away.
In the last ten years, researchers have discovered the first two such objects. They could tell they came from beyond our solar system because they were moving too fast to be orbiting the sun. Astronomers wonder whether there might be many other such objects that have been captured into solar orbit.
In 2025, two researchers from Canada took a first step towards finding out. They used theoretical modeling and computer simulation of the gravitational forces involved to estimate how often objects might reach our solar system from its nearest stellar neighbor, Alpha Centauri.
This system of three stars is located about four light years away. A light year is the distance that light travels in a year, or about six trillion miles. The researchers assumed that Alpha Centauri has as many asteroids and comets as we think the sun does. Under these assumptions, they estimate as many as a million objects at least 300 feet across could have been ejected from the Alpha Centauri system, coasted through the frictionless void of space, and been captured into orbit around the sun.
These would almost certainly be distant orbits, in the cloud of comets far beyond Pluto. But, sometimes comets get kicked into orbits that pass close to the sun, and if that happened to such an object, astronomers could get a good look at it.
A special thanks goes to Dr. Alan Jackson, Department of Physics, Astronomy, and Geosciences, Towson University, Towson, Maryland, for reviewing today's episode!
Further Reading
- Some of Earth’s meteors are probably coming all the way from a neighboring star system
- Interstellar meteors might be coming to Earth from our neighboring star system, IFL
- The solar system is teeming with 1 million ‘alien invaders’ from Alpha Centauri
- 1 million interstellar objects—each larger than the Statue of Liberty—may lurk in the outer solar system
C. R. Gregg and P. A. Wiegert, 2025, A case study of interstellar material delivery: Alpha Centauri, arXiv:2502.03224, https://doi.org/10.48550/arXiv.2502.03224