For over two months, astronomers have been closely following an interstellar object — dubbed 3I/ATLAS — as it screams through the solar system at a breakneck speed.
The unusual visitor was only the third object from beyond the solar system ever detected, following ‘Oumuamua, which was discovered in 2017, and 2I/Borisov in 2019.
Researchers have been fascinated by the object, generally believed to be a comet, finding that it’s made up of far more carbon dioxide than expected.
Now, Harvard astrophysicist Avi Loeb, who has extensively examined the possibility that 3I/ATLAS is an artifact from an advanced extraterrestrial civilization, suggests that the object could be far more massive than previously thought.
By analyzing its trajectory, Loeb and his colleagues found that its “non-gravitational acceleration” was “smaller than 49 feet per day, squared,” in a recent blog post. We also know how much mass it was shedding in the form of gases and dust particles.
From this data, Loeb inferred that the “mass of 3I/ATLAS must be bigger than 33 billion tons.”
“Consequently, the diameter of its solid-density nucleus must be larger than [3.1 miles],” he concluded, roughly at the very top of the range of current estimates, based on Hubble Space Telescope observations.
It’s a notable conclusion, considering that it would make 3I/ATLAS “three to five orders of magnitude” more massive than either ‘Oumuamua and 2I/Borisov, which measured roughly a quarter mile and 0.6 miles in length, respectively.
To Loeb, it’s yet another confounding piece of evidence that highlights the object’s sheer rarity, considering how few interstellar objects we’ve detected so far.
“Given the limited reservoir of heavy elements, we should have discovered on the order of a hundred thousand interstellar objects on the 0.1-kilometer scale of 1I/’Oumuamua before finding 3I/ATLAS, yet we only detected two interstellar objects previously,” he wrote in his blog post.
Loeb has also pointed out that the object’s highly unusual trajectory brings it suspiciously close to Jupiter, Mars, and Venus. In just over a week from now, 3I/ATLAS will come within just 1.67 million miles of Mars’ orbit around the Sun, a “remarkable fine-tuning” of its path, the astronomer previously argued.
The astrohysicist reiterated that it’s an exceedingly rare and exciting opportunity to point the HiRISE camera attached to NASA’s Mars Reconnaissance Orbiter at the unusual visitor to get a more detailed look — which could also allow us to confirm its actual size.
“The amount of sunlight reflected from the brightest pixel in the HiRISE image will constrain further the nucleus surface area for an assumed albedo value,” Loeb wrote.
He even says there’s still a glimmer of hope that 3I/ATLAS was a piece of alien technology intentionally sent to us. If the HiRISE camera were to conclude that the object’s core is “larger than [3.1 miles], then an origin associated with the interstellar mass reservoir of rocky material will be untenable,” Loeb argued.
“Is 3I/ATLAS an unusually massive comet with an unusual chemical composition on an unusually rare trajectory or alien technology?” he concluded. “In both cases, the object could shed CO2 and H2O ices from material that collected on its frozen surface as it plowed through interplanetary and interstellar space.”
“We should not decide about the nature of 3I/ATLAS based on the chemical composition of its skin,” Loeb added, “for the same reason that we should not judge a book by its cover.”
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