Mysterious Interstellar Visitor 3I/ATLAS Shows No Tail — Scientists Weigh In

3I/ATLAS, an object from beyond our solar system, recently passed its nearest point to the Sun and is behaving in unexpected ways — most notably, it lacks a clear cometary tail. Astronomers are gathering observations and debating explanations, from unusual natural processes to more speculative ideas.

What happened

3I/ATLAS passed perihelion on Oct. 29, coming within roughly 203 million kilometers of the Sun, according to Harvard theoretical physicist Dr. Avi Loeb. Observers report that the object showed apparent "non-gravitational acceleration" and appeared bluer than the Sun — both characteristics that are atypical for ordinary comets.

No obvious tail

Contrary to expectations for a sun-approaching comet, recent images show a compact, blob-like source of light rather than a distinct cometary tail. The absence of a visible tail has prompted questions about the object's composition, activity level and surface properties. Several factors — such as small dust production, a very low volatile content, or particle sizes that scatter light differently — could explain the appearance without invoking exotic causes.

Views from experts

"It came from the same direction as the 'Wow' signal that was discovered in 1977, a radio signal that is still enigmatic. We don't know what the source is, but they were within nine degrees of each other. And the question is, were they related? Was this signal related to 3I/ATLAS in any way? So there are lots of anomalies. It should just make us curious." — Dr. Avi Loeb

"We are screwed if it's technological… But, you know, if we survive any such encounter, it should fill us with a sense of humility, with the fact that we do have siblings in our family of intelligent civilizations, and they're more accomplished than we are. That should inspire us to do better." — Dr. Avi Loeb

Other astronomers urge caution. Dr. Ken Gayley, an astronomy professor at the University of Iowa, stresses that the default assumption should be a natural explanation: "We would always start off with the assumption that these are natural objects and we would study them in that way. And if there's really very powerful evidence that they're not, then we might be led toward another direction. But for now, there's still plenty of evidence that these are potentially just completely natural objects."

What we don't know

The intrinsic nature of 3I/ATLAS remains unresolved. Key open questions include whether the observed acceleration is due to outgassing, radiation pressure, or observational bias; what the object's composition and size distribution of dust and ice are; and whether its color and appearance are telling us about surface chemistry or scattering effects. More high-quality observations across wavelengths are needed before drawing firm conclusions.

What’s next

3I/ATLAS will be closest to Earth on Dec. 19, offering astronomers another chance to collect spectra, high-resolution images and brightness measurements that could clarify its properties. Teams around the world are planning follow-up observations to test natural explanations and to constrain any unusual behavior.

Background

The object was discovered by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey from Rio Hurtado, Chile. The designation "I" indicates an interstellar origin — this is the third identified interstellar object after 1I/ʻOumuamua (2017) and 2I/Borisov (2019), hence the name 3I/ATLAS.

Sources

This report summarizes interviews and statements reported by FOX 10 Phoenix and LiveNOW from FOX (Dr. Avi Loeb and Dr. Ken Gayley) and supplemental background from NASA. Additional analyses and peer-reviewed studies may refine these findings as more data arrive.