A new guest in the cosmic neighborhood: The possible extraterrestrial origins of 3I/ATLAS

The object in question is 3I/ATLAS. ATLAS refers to the Asteroid Terrestrial-impact Last Alert System telescope network that helped discover it. The 3I indicates signifies that it is the third such interstellar visitor ever identified, following 1I/Oumuamua and 2I/Borisov..

From the moment it was discovered, 3I/ATLAS was very puzzling. The object is very big and very bright. Loeb estimates that it could be as wide as 20 kilometers (12.4 miles).

This is extremely rare because it may very well be impossible for such a large object of this type to form naturally.

According to Loeb, there isn’t enough rocky material in interstellar space to form objects that massive that would come so close to Earth so frequently.

“If you package all the rocky material in interstellar space into 20-kilometer packages, you would find one every 10,000 years or more,” Loeb said. “Something is really unusual about it – it’s either much smaller or much rarer.”

Some have theorized that it could just be a comet, but Loeb said there is considerable evidence against that.

Another thing that stands out is its brightness. 3I/Atlas is very bright, which, according to Loeb, could indicate that there is something in there creating light. Unlike comets, the brightness doesn’t trail behind the object but rather drops very rapidly.

But those are not the only things that are unusual about 3I/Atlas – there’s also its path.

The odds of this happening naturally are, according to the Harvard astrophysicist, astronomically low.

“It could have arrived at any given time, and there is a chance of one in 20,000 for it to arrive as close as it does to Mars, Venus, and Jupiter,” he said.

“If this was a fine-tuned trajectory that was designed by some intelligence, that would make a lot of sense, because if it wants to release mini-probes or intercept the planets, this is the best approach,” Loeb said. “This is because the mini-probes would move toward the planets instead of chasing them, since they move in the opposite direction.”

Other scientists have been quick to disagree with the possibility that it is alien, maintaining that it has clear signs of being a comet. Observations in late August showed signs of water, cyanide, and carbon dioxide, which are common in comets.

Loeb referred to a system of measurement he created to evaluate interstellar objects, which he dubbed the Loeb Scale. This scale evaluates all interstellar objects on a scale of zero to 10, with zero being an object that is definitely natural. Currently, 3I/ATLAS sits at a four. If it turns out to be nothing more than a comet, which could become apparent as it gets closer to the sun, then it will drop to zero.

How can we tell if it is an alien-made object?

3I/ATLAS will pass Mars on October 3, 2025, and Loeb has asked the team in charge of HiRISE to try to observe the object as it passes.

Another potential tool is the Juno spacecraft currently orbiting Jupiter.

“It was about to be destroyed in mid-September,” Loeb said. “I suggested in a paper that instead of pushing Juno into Jupiter, we should push it away from Jupiter so that it will come closer to 3I/ATLAS.”

Loeb has received support from US Congresswoman Anna Paulina Luna of Florida, who sent a letter to NASA asking to use Juno to observe 3I/ATLAS.

But there is another potential option: sending a radio signal to the object. As fast as 3I/Atlas is going (it moves several times faster than the fastest rockets known to man), the speed of light is even faster. A beam of light containing a radio signal could very well make it all the way to this object, something Loeb compares to a blind date with this interstellar guest.

But that would only make sense if it is indeed some sort of alien probe. If it is just a strange comet, it would be an exercise in futility.

When it comes close to the sun this question could be answered, as the sunlight would heat up the comet, producing a very clear tail.

But if 3I/ATLAS is an interstellar visitor, its orbital path raises a major question: Why is it conspicuously avoiding Earth?

This is impossible to know automatically, even if we were certain that it was an alien spacecraft. However, a possible explanation is the Dark Forest hypothesis.

To understand the Dark Forest hypothesis, one must first understand the Fermi Paradox.

Essentially, scientists had come to an understanding that since life could arise on Earth, the same conditions must logically be present elsewhere in the universe, even in our own Milky Way Galaxy. In fact, it must be so common that life would need to be abundant in the universe, and it would be implausible for it to not have been detected yet.

Then in 1950, Nobel Prize laureate Enrico Fermi allegedly asked, in a discussion with other scientists, the question that gave rise to the paradox: “Where is everybody?”

In other words, if there is such a high likelihood of extraterrestrial life existing in the universe, why has nobody found anything yet? And for that matter, why have they not found us?

This is especially odd, given the fact that while there are billions of stars in our galaxy similar to the sun that also host Earth-like planets, the sun is comparatively young, so civilizations should have already developed on these far-off worlds.

And given how, according to a 2023 peer-reviewed study, the Earth releases so much radio waves from mobile phones that the entire planet is essentially one bright radio anomaly, the fact that we have yet to be discovered by advanced aliens seems odd.

But there are possible solutions to the Fermi Paradox, and the most relevant one for this discussion is the Dark Forest hypothesis.

The theory is that alien civilizations do exist. However, it is in every civilization’s best interest to not be discovered. Because while space is infinite, resources are not, and the intentions of any civilization can never be known for sure – other than the need for survival.

“When you are in a dark forest, you never know if there is an animal that could kill you,” Loeb said. “So you keep quiet, keep a low profile, and you listen. You observe. And if they are observing us, because we were careless in transmitting radio signals over the past century, they might have realized that we are a young technological civilization on a path to become powerful, and so they would like to monitor us. In that case, they would come to visit us without us detecting any prior radio signal from them.”

With that in mind, exiting the Solar System is extremely difficult. Surrounding the Solar System is the Kuiper Belt, a huge ring of dust, asteroids, and comets, much larger than the asteroid belt.

At that speed, flying through the Oort cloud to get to the interstellar medium and the rest of the galaxy would take an additional tens of thousands of years. Actually encountering anything in space could take even longer, if it would ever even happen.

Given how long it takes things to get from place to place in space, by the time humanity actually sends a probe to find alien life, the likelihood is that no one who sent that message would still be alive.

But this is also true of aliens who would send a probe to us. Unless they have developed ways of traveling faster than light or shortcuts such as a wormhole, the odds of whoever sent an alien spacecraft to make first contact with Earth still being alive by the time it gets here are practically nil.

But that doesn’t mean it’s impossible. It may very well be the case – some say it’s even more likely – that an alien spacecraft could be run by artificial intelligence. So, protocols to be prepared for such a scenario are still relevant.

3I/ATLAS is the third interstellar object detected by humanity, all of which were discovered in the last eight years. But Loeb expects that number to increase drastically in the next few years.

“The Rubin Observatory in Chile is expected to find an interstellar object every few months,” he said of the new advanced facility. “That increases the rate of detection by at least two orders of magnitude.

But there is always the chance that even if it is technology, we wouldn’t recognize it as such. And the same could be the case for probes we send into space.