Harvard Expert Avi Loeb Warns Interstellar Visitor 3I/ATLAS May Be by 'Design' — What Does It Mean?

As we end 2025, it's time to think about the most amazing 'blind date' in history: meeting the interstellar interloper 3I/ATLAS. Many people might think that this visitor is a one-of-a-kind cosmic oddity, but Harvard astrophysicist Professor Avi Loeb says that if this object is a natural comet, we are only seeing a small part of a huge, invisible crowd. 3I/ATLAS isn't alone; it could be one of 100 quadrillion similar objects floating around in our own Milky Way galaxy.

The ATLAS survey telescope in Rio Hurtado, Chile, found the interstellar visitor on July 1, 2025. It made its presence known by moving so quickly that it will never be able to escape the sun's gravity. When it was first seen, it was moving at about 137,000 miles per hour. As it went around the sun, it sped up to 153,000 miles per hour.

This last sprint, though, comes after a journey of 8,000 years through the farthest parts of our solar system. On Oct. 29, 2025, the object reached its perihelion, which is about 203 million kilometres from the sun. This distance, which was about 1.36 times the distance between the Earth and the sun, was the middle of its dramatic tour.

The Trillion-Object Secret of 3I/ATLAS

The sheer scale of the population represented by 3I/ATLAS is difficult to fathom. By assuming it is a natural object on a random trajectory, Professor Loeb calculates that a five-year survey capable of finding such an object at a distance of 5 AU implies a hidden multitude. According to his estimates, there are likely a trillion similar objects currently moving through our solar system, extending out to the edge of the Oort Cloud at 100,000 AU.

When we expand this view to the rest of the galaxy, the numbers become even more surreal. If every star in the Milky Way produces a similar trillion-object 'cloud', then the total population of interstellar comets reaches 10^23 — a one followed by 23 zeros. For an object like 3I/ATLAS, which is estimated by the Hubble Space Telescope to be up to 5.6 kilometres in diameter and weigh a billion tons, this means that every star system had to process roughly 10 Earth masses of heavy elements to create this galactic reservoir of ice and rock. In this 'natural' scenario, our visitor is nothing special; a billion similar visits would have occurred throughout the history of the Earth.

Decoding the Technological Intent of 3I/ATLAS

However, there is an alternative that would make our encounter deeply personal. If 3I/ATLAS was not a random wanderer but was instead 'targeting' the inner solar system by technological design, the statistics change entirely. Loeb points to several 'statistically impossible' anomalies to support this: the object's trajectory is aligned within five degrees of our planets' ecliptic plane — an occurrence with only a 0.2% probability.

Furthermore, its arrival was 'fine-tuned' to bring it within tens of millions of kilometres of Mars, Venus, and Jupiter while remaining unobservable from Earth at its closest solar approach. In this case, our region of space is an area of specific interest to an external intelligence, making the visit a high-stakes event that merits a serious emotional and scientific response. Loeb has even warned that the object could be a 'Trojan Horse' or a mothership intended to release mini-probes as it passes Jupiter's Hill Radius in March 2026.

To prepare for future encounters, Loeb proposes a three-layered screening process for our 'interstellar dating partners'. The first layer relies on wide-field survey telescopes like the Rubin Observatory in Chile to spot these objects as they arrive. The second layer would involve a 100-metre-long optical interferometer on the moon — a project currently being considered under NASA's Artemis programme — which could provide high-resolution images to distinguish between a natural rock and a technological artefact.

Finally, the third layer involves interceptor missions that could land on these objects to search for the building blocks of life or, if necessary, employ nuclear measures to mitigate a potential threat. Whether 3I/ATLAS is a natural relic of the Big Bang or a piece of 'alien' technology marked by industrially-produced nickel-iron ratios, it has fundamentally shifted our understanding of our place in the galactic crowd.