Scientists have uncovered a comet on a one-way journey out of our solar system after a close encounter with Saturn.
Designated Comet A117uUD (A117uUD), this cosmic wanderer was first spotted on 14 June 2024 by the Asteroid Terrestrial-impact Last Alert System (ATLAS). By meticulously piecing together 142 observations of the comet, researchers were able to "rewind" its trajectory around the Sun. This revealed a pivotal encounter in 2022 with Saturn, the solar system's second-largest planet, renowned for its dazzling rings.
This meeting with the gas giant flung the comet onto a highly elongated, or elliptical, orbit that will ultimately catapult it into interstellar space, beyond the Sun's grasp. Using models to project the comet's future path, the team discovered that A117uUD will exit the solar system at a remarkable speed of around 6,710 miles per hour (10,800 km/h). This is approximately four and a half times the maximum velocity of a Lockheed Martin F-16 jet fighter.
This marks only the second solar system comet observed in the process of being ejected from our planetary system. The first, Comet C/1980âE1â(Bowell), was propelled onto an escape trajectory by a close encounter with Jupiter on 9 December 1980.
"Our findings show that the case of comet A117uUD mirrors that of C/1980âE1â(Bowell), suggesting that A117uUD is indeed of solar system origin," the research team states in their paper, published in the journal Research Notes of the AAS. "The fact that two such ejections after planetary encounters have been observed within a span of less than 45 years implies that these events are relatively frequent."
An Interloper or a Homebody?
Initially, the team was unsure whether A117uUD was a solar system resident destined to leave home or an interloper from another planetary system. The comet's hyperbolic orbit, typical of objects entering from outside the solar system, hinted at an interstellar origin.
The first confirmed interstellar object discovered by humanity was the peculiarly cigar-shaped asteroid 1I/âOumuamua (âOumuamua), a Hawaiian word roughly translating to "messenger from afar arriving first."
Upon its discovery in 2017, âOumuamua captivated astronomers with its highly unusual shape and the absence of a coma (the halo surrounding comets) or a distinctive cometary tail, despite appearing as a strange comet-asteroid hybrid. It was also accelerating away from the Sun, leading to the now largely dismissed theory that this interplanetary visitor could be an alien spacecraft.
The solution to these unique features was the intense roasting of âOumuamua by cosmic radiation prior to its entry into the solar system, which created and trapped hydrogen within its body. This hydrogen was released and began to spray out of the space rock as it approached the relative warmth of our planetary system, propelling it forward.
âOumuamua is now beyond the orbit of Neptune, traversing the Kuiper Belt, a ring of icy bodies at the outer edge of our solar system. It has passed out of reach of our telescopes and will never return towards Earth or the Sun.
While âOumuamua was the first confirmed interstellar visitor, it was not alone. Comet 2I/Borisov (2I/Borisov) was the second confirmed interstellar object and the first confirmed interstellar comet found within the solar system.
Discovered by Crimean amateur astronomer Gennady Borisov on 30 August 2019, this solar system invader truly eclipsed A117uUD's speed, hurtling through our planetary system at a staggering 110,000 mph. This is 150 times the speed of sound, leaving a Lockheed Martin F-16 in its dust trail, travelling 75 times faster than the jet fighter's top speed.
Like âOumuamua, 2I/Borisov was a transient visitor, briefly captivating astronomers and the public alike before heading towards its solar system exit, never to return.
The encounter between A117uUD and Saturn significantly altered the comet's orbit, preventing the team from reconstructing its path prior to the encounter. However, their analysis was sufficient to confirm that this was not a third interstellar interloper.
Perhaps, one day, the Saturn-ejected comet A117uUD will captivate the astronomers of a distant alien civilisation, billions of years after its discoverers on Earth have vanished.
