Astronomers recently spotted 3I/ATLAS, an interstellar object hurtling through our solar system at an eye-watering 210,000 kilometres per hour. The discovery marks only the third confirmed interstellar visitor, following 'Oumuamua in 2017 and Borisov in 2019. NASA classifies it as a comet, roughly 10 to 24 kilometers across, quietly cruising through space with no immediate threat to Earth.
Harvard astrophysicist Avi Loeb has seized on the object, proposing a more sensational scenario: what if 3I/ATLAS is not a comet at all, but an artificial spacecraft with its own nuclear power source? Loeb points to an unusual brightness at the object's front rather than the trailing tail typical of comets and calculates that this luminosity reaches gigawatt levels. In his analysis, conventional explanations, reflected sunlight, outgassing, even primordial black holes, fall short. Nuclear power, he suggests, is the most plausible culprit.
While this makes for headlines, the claim stretches credulity. Spectral data largely show comet-like characteristics, albeit faint and smeared due to motion, and multiple astronomers have noted that the supposed "forward glow" could easily result from imaging artifacts or natural outgassing processes. The probability calculations Loeb cites, alignment of the orbit with Venus, Mars, and Jupiter, are interesting but not definitive; space is vast, and rare coincidences happen. Extraordinary claims demand extraordinary evidence, and so far, we have none.
Loeb goes further, hypothesising that the object might launch probes toward Earth between November 21 and December 5, 2025. Here, science drifts dangerously close to speculation dressed as prediction. Without direct measurements, redirected spacecraft missions, or verified signals, these scenarios remain exercises in imagination rather than evidence-based science.
The controversy is reminiscent of the hype around 'Oumuamua, which some initially suggested could be a probe. Subsequent analyses largely favoured natural explanations, from tumbling cigar-shaped rocks to icy fragments. Scepticism in astronomy is not cynicism, it is a recognition that even the most intelligent speculation cannot replace empirical verification.
Loeb himself frames his analysis as pedagogical, urging monitoring of 3I/ATLAS for non-gravitational acceleration or other anomalies. That is reasonable. But it is a far cry from asserting artificiality as a probable explanation. The scientific community remains unconvinced, and rightly so: natural explanations are still entirely sufficient to describe what we see.
In the end, 3I/ATLAS is a fascinating object, a reminder that our solar system is not isolated and that interstellar visitors are more than theoretical curiosities. But for now, the leap from comet to nuclear-powered spacecraft is a leap of imagination, not one grounded in the data. Until we can observe the object closely, or detect unequivocal signs of artificiality, it is wiser to keep our feet firmly on Earth, even as our eyes remain fixed on the stars.