Interstellar visitor 3I/ATLAS shows unexpected behavior
A giant interstellar object known as 3I/ATLAS, first spotted racing through the solar system over the summer, exhibited unexpected non-gravitational acceleration and developed a striking blue tint as it passed close to the Sun, scientists report.
Analysis of spacecraft data reported by Harvard astronomer Avi Loeb indicates that NASA observations first flagged the unusual acceleration. Some models suggest that if the effect is caused by intense outgassing, the object could lose roughly half its mass and produce a substantial debris plume in the months following perihelion.
Ground-based telescopes have been unable to observe 3I/ATLAS while it sits nearly behind the Sun, though it is expected to reappear in early December, allowing astronomers on Earth to make direct measurements. Meanwhile, space agencies including NASA and the European Space Agency (ESA) have continued to track the object using spacecraft instruments.
Possible explanations
Researchers are considering multiple explanations for the acceleration and the blue color. Natural scenarios include rapid, asymmetric outgassing or extreme evaporation that could ionize species such as carbon monoxide in the coma, producing a blue glow. One recent paper argues that intense evaporation near perihelion could plausibly produce the observed color and the apparent acceleration.
"Alternatively, the non-gravitational acceleration might be the technological signature of an internal engine," Loeb wrote, noting that a powered source would be an extraordinary alternative if natural explanations fail.
NASA officials have urged caution and skepticism. In response to public questions — including one from a high-profile social media user — NASA Acting Administrator Sean Duffy reiterated that current observations show no evidence of extraterrestrial threat.
"@NASA's observations show that this is the third interstellar comet to pass through our solar system," Duffy wrote on X. "No aliens. No threat to life here on Earth."
Key dates and what to watch for
- Perihelion (closest approach to the Sun): Oct. 30 — about 130 million miles (210 million km).
- ESA's JUICE spacecraft planned observations: Nov. 2 and Nov. 25.
- Expected reappearance from behind the Sun: early December, when ground telescopes can resume monitoring.
- Closest approach to Earth: Dec. 19 — roughly 167 million miles (about 269 million km).
If 3I/ATLAS returns to view without the predicted mass loss or debris, scientists will be able to test hypotheses more rigorously and narrow down whether the object is behaving like a typical comet or displaying anomalous properties that require alternative explanations.
Bottom line: The object’s acceleration and blue color are intriguing but not yet definitive. Several natural mechanisms could explain the observations, though researchers remain open to further evidence once the object is better observed in December.
