Our third interstellar visitor lost a huge amount of mass after passing the Sun, and appeared to us with an anti-tail and a “smoking” tail. “This would mean that 3I/ATLAS exploded at perihelion and we are witnessing the resulting fireworks,” says Avi Loeb.
The mysterious interstellar object recently passed its closest point to the Sun, or perihelionand became brighter in observations as solar radiation caused it to release gases at an immense rate.
Upon resurfacing after its passage behind the Sun, the object, considered a comet (by almost all astronomers), it appears to have lost an impressive amount of mass.
A lost mass is so muchin fact, that the Harvard astrophysicist and keen observer of 3I/ATLAS, Avi Loebsuggests it may have just fragmented in more than a dozen pieces.
News captured last Sunday by British astronomers Michael Buechner e Frank Niebling show the celestial body gaining a huge “reverse tail”or “anti-tail”, and an independent “smoking” trail.
These jets extend to approximately 1 million kilometers towards the Sun and 3 million kilometers in the opposite direction, notes Loeb in a blog post.
“For a natural cometit is expected that, at the distance at which 3I/ATLAS is from the Sun, the ejection speed of the jets will be 400 meters per second. At this speed, the jets must have persisted for 1 to 3 months”, details Loeb, who — for 9 reasons.
However, according to the British astronomer’s calculations, 3I/ATLAS would have needed to absorb a enormous amount of energy from the Sun to be able to sublimate the enormous amounts of carbon dioxide ice and water needed to lose such a large proportion of its mass.
“At its perihelion distance, the Sun provided 700 joules per m² per second“, wrote Loeb. “This means that the absorption area of 3I/ATLAS must have been greater than 1600 kilometers km²”, that is, the equivalent of a sphere with a diameter of 23 kilometers.
This value is four times bigger than the previous estimate of the object’s size, calculated by at least 5 kilometers in diameterwith a mass of at least 33 billion tonsnote o Futurism.
Although solar system comets are expected to lose mass as they approach the Sun, the 3I/ATLAS continues to seem like an exception.
“The surface area required of 3I/ATLAS to provide the mass loss inferred from the most recent post-perihelion image is at least 16 times larger than the upper limit here derived from your July 21, 2025 Hubble image,” Loeb wrote. “When the Webb data was collected on August 6, 2025, 3I/ATLAS lost only 150 kg per second“.
In other words, the mysterious visitor went from losing several hundred kilograms per second in August, to now being, close to its perihelion, aa lose 2 thousand tons per second — “a dramatic increase”, according to Loeb.
“Is this dramatic loss of mass and the brightness of 3I/ATLAS at perihelion a evidence that it disintegrated?”, asks the astronomer. “Fragmentation would increase the surface area of its material.”
Loeb suggests that 3I/ATLAS may have divided into at least 16 pieces equal, “and probably many more“, which would mean that 3I/ATLAS exploded at perihelion and we are witnessing the resulting fireworks.”
Despite evidence that the comet may have exploded, the British astronomer not yet willing to discard that 3I/ATLAS could be “something different from a natural comet” — if further observations reveal that it was not decimated by the Sun and maintained its integrity as a single body.
Fortunately, we will have several opportunities to take a closer look at the mysterious interstellar visitor: 3I/ATLAS is expected to reach the closest point to Earth at December 19th. How much of its core will remain by then remains to be seen.
