A team of astronomers has attempted to explain an unusually high-speed comet, finding that it was likely sent on its hyperbolic trajectory following a close encounter with Saturn in 2022.
On June 14, 2024, Comet A117uUD was first spotted by the Asteroid Terrestrial-impact Last Alert System (ATLAS). Over the next month, astronomers made 145 observations of the object, giving them a pretty good initial picture of its path. Analyzing the data, it appears the comet is on a “hyperbolic trajectory”, meaning that it is moving at speeds that will allow it to exit the Solar System and enter interstellar space.
In a new paper, astronomers attempted to figure out what caused its unusually high speed. Astronomers have so far seen two interstellar objects passing through our Solar System, so it was possible that Comet A117uUD could be another.
“In addition, passing stars or the Galactic tide may send Oort cloud comets toward the inner solar system along hyperbolic trajectories,” the team explains in their paper.
Another possibility is that it was sent on its hyperbolic trajectory following an encounter with one of our gas giants. As smaller objects approach a planet, momentum is transferred from the planet to the object, slowing the orbit of the planet a tiny amount in exchange for a boost in velocity to the object.
So far, we have only seen one comet – Comet C/1980 E1 – which has been set on an interstellar course by such an encounter, after it passed by Jupiter in 1980. Attempting to derive Comet A117uUD’s previous positions, the new team believes Saturn is responsible for yeeting it on a course out of the Solar System.
“The comet experienced a very close encounter with Saturn in 2022 that makes it difficult to reconstruct the pre-encounter orbit,” the team explained in their paper, though they believe its previous orbit resembled those of retrograde Centaurs – small bodies that orbit between Jupiter and Neptune – or comets.
“Our results show that the case of comet A117uUD is similar to that of C/1980 E1 (Bowell), disfavoring an extrasolar origin for A117uUD,” the team concludes. “The fact that two ejections after planetary encounter were observed in less than 45 yr suggests that such events are relatively frequent.”
The study is published in Research Notes of the AAS
