Comet 3I/Atlas is emitting a radio signal

This year’s most sensational story for astronomers is the discovery of comet 3I/ATLAS, which was first observed on July 1, 2025 by NASA’s Asteroid Terrestrial-Impact Last Alert System (ATLAS). Although comets regularly pass by Earth, the most famous being Halley’s Comet, there is something extra-special about this new discovery. Halley’s and other famous comets originated within our solar system, from which the Sun, Earth, and all other planets were formed. What makes 3I/ATLAS so fascinating is that it originated somewhere outside the Solar System, and made its way here through interstellar space. As if this wasn’t an exciting enough discovery, a radio telescope noticed that the comet was emitting something.

South Africa’s MeerKAT radio telescope picked up on 3I/ATLAS in late October, as the comet neared its closest point to the Sun. The discovery was widely reported as radio signals emitting from 3I/ATLAS, leading conspiracy theorists to speculate that the object might actually be a piece of alien technology. However this is not quite right. Technically, everything emits electromagnetic radiation, and the audio transmission detected by MeerKAT was nothing like what we hear on a car radio. What it actually found was a gap in the radio spectrum caused by the absorption of radio waves by OH molecules, also known as hydroxyl radicals. OH molecules—remnants of water broken down by solar radiation—are regularly observed in comets that pass within Earth’s orbit, putting to bed any speculation that 3I/ATLAS is anything other than a comet. However, this does not answer the question of where 3I/ATLAS came from.

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Astronomers are still not sure where 3I/ATLAS came from

The 3I/ATLAS discovery marked the third time astronomers have observed an interstellar object passing through our solar system. The “3I” in its name actually stands for “Third Interstellar” for this reason. The previous two interstellar objects observed by astronauts were 1I/’Oumuamua and 2I/Borisov, discovered in 2017 and 2019 respectively. The fact that all known interstellar visitors to our solar system have been discovered in the last decade is a sign of great advances in astronomical technology, but it also means that we have been able to gather very little data about interstellar comets so far. However, one thing stands out. Both 1I/’Oumuamua and 2I/Borisov are coming from the direction of the center of the Milky Way, but 3I/ATLAS is coming from a perpendicular angle.

Based on the trajectory, it is likely that the comet originated in a part of the galaxy that astronomers have not yet observed. NASA is collecting 3I/ATLAS images, as is the European Space Agency, and both expect to have more satellite and probe data ready for analysis in early 2026; However, it is highly unlikely that we will ever be able to discover the exact origin of comets. While scientists don’t know where it came from, they have a pretty good idea where 3I/ATLAS is going, and you can be sure it won’t hit Earth. In fact, comets don’t even come as close to us as the Sun.

Why some people still think that 3I/ATLAS is a piece of alien technology

The intrusion of an interstellar object into our solar system immediately caught the attention of all alien enthusiasts out there, and not just the usual podcast conspiracists. A professor at the Harvard Center for Astrophysics is arguing that 3I/ATLAS could be a piece of alien technology. Professor Avi Loeb has published several articles on his blog about interstellar objects, going against the consensus of his peers in the scientific community. He argues that 3I/ATLAS exhibits more anomalies than the previous two interstellar comets tracked through our Solar System. Compared to that pair, the 3I/ATLAS is much larger, but still goes faster. He also notes that the gas plume surrounding 3I/ATLAS contains similar levels of nickel to industrial alloys.

The newly recorded radio signals from 3I/ATLAS are another dent in Loeb’s theory, which has been roundly rebuked by other astrophysicists. Counterarguments point out that comets often show inconsistent characteristics. It is impossible to tell what is normal and what is abnormal, and this is especially true in the case of interstellar comets. Loeb really hits the nail on the head in an article titled The Tale of 3I/ATLAS and the Sterile Neutrinos, in which he asks, “How can one claim to be an expert on interstellar objects when the sample size includes only two known examples?” In all likelihood, many of our questions about 3I/ATLAS will not be answered until we observe other interstellar comets in the future.

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