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Massive comet zooming through solar system could be alien technology, Harvard astrophysicist says

Published September 30, 2025 6:21 PM MST

A comet traveling outside the solar system and heading toward the Earth is much larger than scientists first believed, a scientist has detailed in a new report.

Avi Loeb claims the comet could even be an artifact of alien technology rather than a natural body because it weighs more than 33 billion tons and spans at least 3.1 miles across.

The object, named 3I/ATLAS, is only the third interstellar visitor ever detected, after Oumuamua in 2017 and 2I/Borisov in 2019. 

The astrophysicist also revealed in a Medium blog post that new data and measurements indicate the comet’s nucleus is more massive than first estimated.

3I/ATLAS was spotted in July with observations showing the comet is shedding huge amounts of carbon dioxide and dust as it races toward the Sun. 

Loeb and his colleagues calculated a slight "non-gravitational acceleration" in its movement caused by "outgassing" which suggests the object must be far heavier than early models assumed.

ASTRONOMERS MAKE GROUNDBREAKING DISCOVERY ABOUT LARGEST COMET EVER OBSERVED FLYING THROUGH DEEP SPACE

The comet dwarfs Oumuamua, just a quarter-mile long, and Borisov, about 0.6 miles across. 

Comet C/2023 A3 (Tsuchinshan-ATLAS) appears in the sky over Molfetta, Italy, on September 28, 2024. (Getty  Images)

"This makes 3I/ATLAS three to five orders of magnitude more massive than the previous two interstellar objects we’ve observed," Loeb wrote in his post.

ANCIENT ‘STICK FIGURES’ ON BEACH ONCE AGAIN VISIBLE AT TOURIST DESTINATION

Next week the comet will pass within 1.67 million miles of Mars’ orbit while also coming close to both Jupiter and Venus. 

Loeb has urged NASA to turn the HiRISE camera on the Mars Reconnaissance Orbiter towards the object and said that even a single bright pixel could fine tune estimates of its true dimensions.

"We should not decide about the nature of 3I/ATLAS based on the chemical composition of its skin," Loeb wrote. 

"For the same reason, we should not judge a book by its cover," he added.

Find more updates on this story at FOXNews.com.

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