Mysterious interstellar object 3I/ATLAS recently made its closest pass of the Sun, or perihelion, brightening up in observations as solar radiation caused it to shed gases at an immense rate.
The object, widely believed to be a comet, is losing a staggering amount of mass as it reemerges from behind the Sun — so much, in fact, that Harvard astrophysicist and close 3I/ATLAS watcher Avi Loeb suggests that it may have just broken up into well over a dozen pieces.
New images taken by British astronomers Michael Buechner and Frank Niebling show the object growing a massive “anti-tail” and a separate, “smoking” trail, jets that extend approximately 620,000 miles towards the Sun and 1,860,000 miles in the opposite direction, respectively, as Loeb notes in a new blog post.
“For a natural comet, the outflow velocity of the jets is expected to be [0.248 miles] per second… at the distance of 3I/ATLAS from the Sun,” he added. “At that speed, the jets must have persisted over a timescale of 1–3 months.”
However, according to Loeb’s calculations, 3I/ATLAS would’ve needed to absorb an enormous amount of energy from the Sun in order to sublimate the copious amounts of carbon dioxide ice and water ice required to lose a such huge proportion of its mass.
“At its perihelion distance, the Sun provided 700 Joules per square meter per second,” Loeb wrote. “This means that the absorbing area of 3I/ATLAS must have been larger than [617 square miles],” roughly equivalent to a sphere with a diameter of 14.3 miles.
That’s four times as large as his previous estimate of the object measuring at least 3.1 miles across, with a mass of at least 33 billion tons.
While solar system comets are expected to shed mass as they approach the Sun, 3I/ATLAS still appears to be an outlier.
“The required surface area of 3I/ATLAS to provide the inferred mass loss from the latest post-perihelion image, is at least 16 times larger than the upper limit derived here from its Hubble image on July 21, 2025,” Loeb wrote. “When the Webb data was taken on August 6, 2025, 3I/ATLAS lost only [330 pounds] per second.”
In other words, the mysterious visitor went from shedding several hundred pounds a second in August to roughly 4.4 million pounds a second near its perihelion, a “dramatic increase,” per Loeb.
“Was the dramatic mass loss and brightening of 3I/ATLAS at perihelion evidence that it disintegrated?” the astronomer questioned. “Breakup into fragments would have increased the surface area of its material.”
Loeb suggests that 3I/ATLAS could have split up into “at least 16 equal pieces, and likely many more,” which “would mean that 3I/ATLAS exploded at perihelion and we are witnessing the resulting fireworks.”
Alternatively, the astronomer isn’t willing to rule out that 3I/ATLAS may be “something other than a natural comet” if “upcoming observations would reveal that 3I/ATLAS was not decimated by the Sun and maintained its integrity as a single body.”
Ever since its discovery, Loeb has proffered a series of eyebrow-raising suggestions about the object — most notably that it could be a giant alien spacecraft, citing its unusual properties ranging from its enormous suspected mass to its trajectory that’s closely aligned with the solar system’s planets.
“Technological thrusters require a much smaller mass loss in order to produce the observed jets around 3I/ATLAS,” he wrote in his latest blog. “Chemical rockets are propelled by an exhaust speed of [1.86 to 3.1 miles per second], which is ten times larger than the maximum ejection speed of volatiles sublimated by sunlight from natural cometary surfaces.”
“Alien-tech thrusters might employ yet higher exhaust speeds, reducing the required mass loss by several orders of magnitude and making the required fuel a small [proportion] of the spacecraft mass,” he suggested.
Fortunately, we‘ll have several more opportunities to get a closer look. 3I/ATLAS is expected to make its closest pass of the Earth on December 19 and Jupiter in March. How much of its nucleus will be left by that time remains to be seen.
More on 3I/ATLAS: NASA Withholding New Images of Mysterious Object From Beyond Solar System