The interstellar object known as 3I/ATLAS, detected in July by the Chilean Asteroid Terrestrial-impact Warning System (ATLAS) observatory, has been the subject of intense speculation. A radio signal captured by the MeerKAT radio telescope in South Africa provides new clues about its nature and definitively disproves speculations that experts have described as outlandish and spectacular.
The radio telescope, composed of 64 antennas and located 600 kilometers from Cape Town, identified the signal on October 24. This is an absorption of radio waves caused by hydroxyl (OH) molecules, which result from the dissociation of water when a comet’s ice sublimates as it approaches the Sun.
According to Michael Küppers, a scientist at the European Space Agency (ESA), this observation confirms that one of the main components of the comet’s nucleus ices is water, “which is normal for a comet.” Küppers adds that similar signals have been detected in numerous celestial bodies in the solar system, reinforcing the interpretation that it is a natural object and not something exceptional, as some speculative hypotheses suggested, including the possibility of an extraterrestrial spacecraft.
When the comet disappeared from view behind the Sun, some speculated that it was a spacecraft hiding. But after it reappeared on November 4, that hypothesis vanished. It was following its expected trajectory: it was where the calculations predicted it would be. And the signals it emitted showed a natural pattern.
The ESA scientist explains that the recorded emissions are spectral lines, a type of molecular fingerprint. “All molecules have characteristic lines at different wavelengths,” he says. “In the case of OH emissions, these are very long wavelengths, corresponding to changes in the molecule’s rotational state.” Detecting them requires the comet to be active enough to release a significant amount of gas.
For researcher Javier Peralta, an expert in planetary atmospheres, it is best to carry out these types of detections when the comet is closest to the Sun (at its perihelion). “At that time, it is expected that, while water is sublimating, one of the gases formed will be hydroxyl,” he indicates.
