In June 2025, astronomers spotted an object the size of Manhattan hurtling toward our solar system at 140,000 mph: 3I/Atlas. The “3I/” in its name is because it’s only the third object from interstellar space we’ve had the technology to observe. If it’s just a big, fast comet zipping between solar systems, it’s already one of the coolest events in astronomy. But Harvard professor Avi Loeb has suggested it might be something else: an alien spaceship. He’s even joked that Oct. 29 may be such an important date for the object that “if you want to take a vacation, take it before.”

Why some think 3I/Atlas could be an alien spaceship

First and foremost, what’s the argument for this interstellar visitor being artificial? Professor Loeb made three interesting observations:

1. He doubts there’s enough material floating in space for something like this to form naturally, calling it “too large for an interstellar asteroid.”

2. Comets are mostly ice and cast long tails as they melt, but at first 3I/Atlas showed “no spectral features of cometary gas.” Now, the outgassing seems to be coming from the front of the object, and analysis reveals molecules that are byproducts of industrial processes on Earth—not naturally forming.

3. 3I/Atlas’ flight path takes it right by Jupiter, Mars, and Venus—a suspiciously perfect route to scout out the solar system. Loeb claims this would be “a one-in-500 coincidence” if it occurred by chance.

Authorities aren’t worried about 3I/Atlas

That flight path also means 3I/Atlas won’t get closer than 170 million miles from Earth before it zips back out of the solar system. No one at NASA is ringing any alarm bells.

Thomas Statler, head of NASA’s Solar System Small Bodies program, isn’t buying the alien spaceship theory. “It does comet things. It very, very strongly resembles, in just about every way, the comets that we know.”

He admits it’s a bit unique—as to be expected from only the third interstellar body we’ve ever observed. “It has some interesting properties that are a little bit different from our solar system comets, but it behaves like a comet.” His verdict? “A natural body.”

Science educator Neil deGrasse Tyson notes that the three interstellar objects we’ve observed “don’t match some of our models for what comets and asteroids should do.” He adds, “I’m delighted that they’re finally in the catalog,” because investigating mysteries is what advances science. But he warns that jumping to a conclusion—such as calling 3I/Atlas an alien spaceship—“as a substitute for the simple statement, ‘I don’t know what it is,’” is counterproductive to the scientific process.

While most of the scientific community refers to 3I/Atlas as a very interesting comet, Professor Avi Loeb continues to present theories on how and why it might be an alien spaceship. This makes sense: among the many hats he wears, Loeb is the head of the Galileo Project, which searches for extraterrestrial technology. Discussing how we might someday identify an alien spaceship is part of his job. Lately, he’s been focusing on 3I/Atlas’ upcoming moment of perihelion.

What’s 3I/Atlas doing on Oct. 29?

On Oct. 29, 3I/Atlas will reach its closest point to the sun. This will also be the fastest speed it achieves in our solar system before it slingshots around our star and races off in a different direction. Loeb says one suspicious aspect of 3I/Atlas’ flight path is that it’s hitting perihelion while the sun blocks it from Earth’s view.

Loeb explains, “It is most energy-efficient for a spacecraft engine to burn its fuel when its orbital velocity is greatest.” This is called the Oberth effect, and it suggests that if 3I/Atlas were going to make any course correction, it would probably do so on Oct. 29. Changing course would prove it’s not a “natural body.” But that’s not all.

Loeb also speculates that 3I/Atlas may not use the moment of perihelion to change its own course. “If 3I/Atlas is a massive mothership, it will likely continue along its original gravitational path and ultimately exit the solar system,” he theorizes. “In that case, the Oberth maneuver might apply to the mini-probes it releases at perihelion toward solar system planets.”

Translation: If 3I/Atlas is going to drop probes to explore more of our solar system, it would be most efficient for those probes to detach when the mothership is traveling at top speed. They’ll burn the lowest amount of fuel possible as they head toward their targets.

Loeb joked with one interviewer, “If you want to take a vacation, take it before [Oct. 29], because who knows what will happen?”

All in all, most scientists agree that 3I/Atlas isn’t an alien spaceship. Professor Loeb continues to speak with the media and use this opportunity to present different theories on what an alien spaceship might look like if it were to enter our solar system. Either way, it’s certainly an intriguing conversation. You can see Professor Loeb interviewed in the video embedded below.