When astronomers discovered 3I/ATLAS last July, they thought it would be another interstellar visitor with oddities, like Borisov or ʻOumuamua. But they didn’t imagine it would be so disconcerting. This comet arrived wanting to put on a big show. First, because It is enormous: between 10 and 30 kilometers of corethe largest we have seen come from another star system. Second, because moves at more than 210,000 km/has if he was in a hurry to return home. And third, because he just did something that has scientists scratching their heads: has changed its trajectory without gravity having anything to do with it.
In theory, comets are obedient: they follow the curve marked by gravity, like cars without a steering wheel on a cosmic highway. But 3I/ATLAS decided to go off the rails. Because? The official explanation is “rocket effect”: When the Sun heats the ice, the comet expels gas and dust, and that jet pushes it a little. Until then, everything is normal. The strange thing is the magnitude of the thrust. To justify the change, should have lost a sixth of its mass in a few weeks. And here comes the incredible: that gas cloud is not there.
Imagine that you have a 1,000 kilo car and, to change lanes, you need it to lose 160 kilos in a matter of days. That’s the thing about 3I/ATLAS: to explain the deviation, it should have ejected millions of tons of ice and dust. And when a comet does that, it shows: a huge cloud forms around it, like a bright aura that can be seen even with modest telescopes. But the most powerful instruments—including the James Webb—have not detected the volume of gas that should accompany such a loss of mass. It’s like someone telling you that your car has lost 160 kilos, but it’s still intact and there are no parts lying on the road.
That’s why scientists are worried. Avi Loebthe astrophysicist who never bites his tongue, said it clearly: “If that cloud does not appear in December, traditional physics runs out of excuses”. Loeb was already controversial with ʻOumuamua, suggesting it could be alien technology. Now get back to it: “I’m not saying it’s a ship, but if we don’t find the explanation, we’ll have to look for unusual solutions.”.
Meanwhile, the comet continues to deliver rarities. In July he looked an anti-colaa tail pointing towards the Sun, as if to defy cometary logic. In October, when it touched perihelion—the closest point to the Sun— became bluer than our starsomething no comet had done before. And just in case the show was missing, its brightness shot up suddenly, as if someone had turned the volume up to maximum. The spectra show emissions dominated by carbon and traces of ionized nickel, something never seen in comets in the Solar System. What does it mean? That it formed in an environment very different from ours, perhaps on the icy outskirts of another star system.
The debate is served
On the one hand, there are those who see mystery in every piece of information. “The non-gravitational acceleration is too large to be explained by outgassing”Loeb insists. Others point to the exotic composition: “If there is more CO₂ than water, the dynamics may be different”they say from the Max Planck Institute. And then there are those who ask for calm: “There is no evidence of artificial propulsion. Most likely we are seeing natural processes that we still do not understand well”says NASA. For them, the cloud may appear later, or the ejected material may be invisible at certain wavelengths. In short: mystery yes, but with feet on Earth. Most astronomers consider it to be a natural comet, although with little-known processes. As Karen Meech, a veteran in the study of interstellar objects, concluded: “Science doesn’t need aliens to be fascinating”.
And now what? The next chapter arrives on November 11when it will be visible again before dawn. But the key date is December 19when it will reach its closest point with the earth: 269 million kilometers. That day we will know if the gas cloud appears that would confirm the natural hypothesis… or if the mystery becomes bigger. As one JPL researcher said, almost with amazement: “This comet is teaching us that the universe still holds surprises”.
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In space there are no referees, but 3I/ATLAS just broke the rules. If we don’t see that cloud in December, get ready: science will have to rewrite the manual. And when it does, this comet will already be far away, heading to a place from which it will never return. Its orbit is hyperbolicwhich means that, after this fleeting step, it will disappear into deep space. If we don’t reveal its secrets now, they will be lost forever.
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