First ‘Oumuamua, then Borisov, and now ATLAS have shown us that interstellar interlopers are real. Here’s what the newest one teaches us.
It wasn’t all that long ago — less than 10 years ago, in fact — that all the object we had ever seen in the Solar System originated from within the Solar System. The planets, moons, and dwarf planets all revolved around their parent bodies according to Newton’s law of gravity: in elliptical orbits. Asteroids and Kuiper belt objects largely orbited the Sun in belts (with centaurs in between them), while occasional gravitational interactions would hurl one of those objects, or a farther-flung one from the Oort cloud, towards the inner Solar System, where they would brighten, potentially develop tails, create debris stream, and even sometimes would give rise to meteor showers. From antiquity until 2016, this was the story of every Solar System object we saw.
But then in 2017, all of that began to change. Our first interstellar interloper, ‘Oumuamua, was discovered: a small (about ~100 meters across), elongated, oddly accelerating object was moving far too quickly to have been a perturbed Solar System object. Instead, it must have had an interstellar origin. A couple of years later, Borisov…
