NASA Detects New Interstellar Visitor to Our Solar System: Could It Be an Alien Probe?

3I/ATLAS is a fast, ancient interstellar object. Its odd features fuel both scientific study and speculation.

On July 1, astronomers detected a strange, fast-moving object racing toward the Sun. Named 3I/ATLAS, it stood out for one remarkable reason: its orbit revealed that it had arrived from beyond our Solar System.

This marked only the third confirmed discovery of an interstellar object, and its properties were highly unusual.

3I/ATLAS breaking records

Measurements showed 3I/ATLAS speeding through space at about 245,000 kilometers per hour, making it the fastest body ever recorded within our Solar System.

Its size was equally striking. Early estimates suggest it could span up to 20 kilometers, and scientists believe it may predate the Sun itself.

Could it be alien?

Astronomers typically assume that new objects are made of rock or ice. Yet the unusual characteristics of 3I/ATLAS have led some to speculate that it might be something more.

Harvard astrophysicist Avi Loeb and colleagues recently posted a paper to the arXiv preprint server titled Is the Interstellar Object 3I/ATLAS Alien Technology? (The paper has not yet been peer reviewed.)

Loeb is a controversial figure among astronomers and astrophysicists. He has previously suggested that the first known interstellar object, 1I/ʻOumuamua, discovered in 2017, may also have been an alien craft.

Among other oddities, Loeb suggests may be signs of deliberate alien origin, he notes the orbit of 3I/ATLAS takes it improbably close to Venus, Mars and Jupiter.

We’ve sent out our own alien probes

The idea of alien probes wandering the cosmos may sound strange, but humans sent out a few ourselves in the 1970s. Both Voyager 1 and 2 have officially left our Solar System, and Pioneer 10 and 11 are not far behind.

So it’s not a stretch to think that alien civilisations – if they exist – would have launched their own galactic explorers.

However, this brings us to a crucial question: short of little green men popping out to say hello, how would we actually know if 3I/ATLAS, or any other interstellar object, was an alien probe?

Detecting alien probes 101

The first step is simply detection. Most objects in our Solar System do not produce light but are visible only by reflecting sunlight.

Larger bodies reflect more light, making them easier to spot, so most of what we detect at great distances are bigger asteroids or comets.

Smaller objects are much harder to find. Currently, we can only track bodies as small as 10 to 20 meters across out to the distance of Jupiter.

Our own Voyager probes are roughly 10 meters in size (including their radio antennas). If an alien probe were similar, we would not likely notice it until it was already in the asteroid belt between Mars and Jupiter.

Signs of a true probe

If something unusual were observed, the next step would be to distinguish between a natural body and a technological one.

Because a natural explanation is most likely, scientists would first look for signs consistent with ordinary objects. For instance, a visible “tail” of gas, like that produced by comets, would point toward a non-alien origin.

However, we might also want to look for hints of alien origin. One very strong piece of evidence would be any kind of radio waves coming from the probe as a form of communication. This is assuming the probe was still in working order, and not completely defunct.

We might also look for signs of electrostatic discharge caused by sunlight hitting the probe.

Another dead giveaway would be signs of manoeuvring or propulsion. An active probe might try to correct its course or reposition its antennas to send and receive signals to and from its origin.

And a genuine smoking gun would be an approach to Earth in a stable orbit. Not to brag, but Earth is genuinely the most interesting place in the Solar System – we have water, a healthy atmosphere, a strong magnetic field, and life. A probe with any decision-making capacity would likely want to investigate and collect data about our interesting little planet.

We may never know

Without clear signs one way or the other, however, it may be impossible to know if some interstellar objects are natural or alien-made.

Objects like 3I/ATLAS remind us that space is vast, strange, and full of surprises. Most of them have natural explanations. But the strangest objects are worth a second look.

For now, 3I/ATLAS is likely just an unusually fast, old, and icy visitor from a distant system. But it also serves as a test case: a chance to refine the way we search, observe, and ask questions about the universe.

Reference: “Is the Interstellar Object 3I/ATLAS Alien Technology?” by Adam Hibberd, Adam Crowl and Abraham Loeb, 21 July 2025, arXiv.
DOI: 10.48550/arXiv.2507.12213

Adapted from an article originally published in The Conversation.

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