For only the third time in history, astronomers have detected a new interstellar visitor — an object from another star — blitzing into our solar system.
First named A11pl3Z and now designated as 3I/ATLAS , the comet was spotted by a survey telescope in Chile on July 1 and confirmed by the International Astronomical Union’s Minor Planet Center the same day. To piece together its trajectory, astronomers dug through older sky surveys and found its position as early as mid-June.
Because 3I/ATLAS seems to be hurtling in nearly a straight line through the solar system and going so fast that the sun’s gravity can’t capture it, astronomers are certain the object has alien origins — it came from another star system. The object could be as wide as 20 kilometers and is currently just inside the orbit of Jupiter. It is projected to get closest to the sun in October.
The first known interstellar visitor, a bizarre, asteroid-like object named ‘Oumuamua coming from the direction of the constellation Lyra, was spotted in October 2017. Because ‘Oumuamua receded from view a mere 2.5 months after its discovery, astronomers caught only fleeting glimpses of the object, sparking many theories as to what it actually was. A second object, 2I/Borisov, was first glimpsed in August 2019. It was later confirmed to be a rogue comet from the constellation Cassiopeia.
“What’s amazing [about 3I/ATLAS ] is we discovered this on its way into the solar system,” says Pamela Gay, an Illinois-based astronomer with the Planetary Science Institute. That means scientists will have ample time to observe its path past the sun. 3I/ATLAS will likely be visible from Earth through 2026.
But astronomers aren’t sitting on their heels either. “The hurry at the minute is that we want to observe it before it heats up as it heads into the inner solar system,” says Chris Lintott, an astronomer at the University of Oxford. “We’re interested in it as a frozen relic of another planetary system, not a frozen relic of a planetary system that’s been nicely baked by our sun.”
Further observations will help determine 3I/ATLAS’s composition, a “rare chance to get data about another solar system that we can get in no other way,” Gay says. Such information could illuminate how planets form throughout the Milky Way.
Astronomers hope to glimpse more interstellar visitors — especially with the increased role of citizen scientists and new facilities like the Vera Rubin Observatory in Chile, which will start taking science data this year. Catching 3I/ATLAS before then was a stroke of luck, Lintott says.
“I heard about this object about 30 seconds after I woke up, and I laughed out loud,” he says. “We’d reconciled ourselves to the fact that we were going to wait for the Vera Rubin Observatory to switch on [to find another interstellar object], and to have something else find an interstellar object this week was like the astronomy gods laughing at us.”
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