An interstellar comet on a trajectory toward Earth is significantly larger than initial estimates, according to a new report from Harvard astrophysicist Avi Loeb.
The object, designated 3I/ATLAS, is estimated to weigh over 33 billion tons and measure at least 3.1 miles in diameter, prompting Loeb to speculate that it could be an extraterrestrial artifact rather than a natural comet.
Spotted in July, 3I/ATLAS is only the third interstellar visitor ever detected in our solar system, following the discoveries of Oumuamua in 2017 and 2I/Borisov in 2019.
Loeb and his colleagues observed the comet shedding large amounts of carbon dioxide and dust as it approaches the sun. They calculated a slight “non-gravitational acceleration” in its trajectory caused by this outgassing, leading them to conclude that the object’s nucleus is far more massive than previously thought.
The immense scale of 3I/ATLAS dwarfs its predecessors; Oumuamua was roughly a quarter-mile long, and Borisov was about 0.6 miles across. Loeb noted that this makes the new object “three to five orders of magnitude more massive” than the other two.
The comet is expected to pass within 1.67 million miles of Mars’ orbit next week, with its path also bringing it near Jupiter and Venus. Given its proximity, Loeb has urged NASA to use the HiRISE camera on its Mars Reconnaissance Orbiter to capture an image of the object. He argues that even a single bright pixel of data could help scientists refine estimates of its true size.
Insisting that its surface composition might not reveal its true nature, Loeb cautioned, “We should not decide about the nature of 3I/ATLAS based on the chemical composition of its skin… we should not judge a book by its cover.”
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