The mysterious interstellar object streaking through our solar system has a hidden companion that could collide with Mars within weeks.

Respected Harvard astrophysicist Avi Loeb has proposed a shocking new theory: the massive object approaching Earth could be an extraterrestrial craft. This idea challenges traditional beliefs about the object’s nature.

Scientists and astronomers have largely accepted the unidentified object, referred to as 3I/ATLAS, as a sizable frozen comet emitting significant amounts of carbon dioxide gas (CO2).

Nevertheless, Professor Loeb has noted several unusual aspects, such as its distinctive flight path, which brings it close to multiple planets, suggesting it might have been artificially created.

Now, Loeb has written a new paper theorizing that there is an unseen ‘precursor mini-probe’ traveling ahead of 3I/ATLAS as it makes its closest approach to Mars.

On October 3, 2025, 3I/ATLAS is projected to pass within 18 million miles of Mars, close enough for detailed images to be taken by a Mars-orbiting camera called HiRISE. 

If the comet is actually a spacecraft, however, Loeb said the object may adjust its mini-probe’s course to intentionally fly near or even crash into Mars.

Loeb added that the purpose of such a probe could be to explore or investigate Mars, possibly sent by an advanced civilization to study the planet.

The latest observations of 3I/ATLAS (circled) showed the comet rapidly became five times brighter as it flew closer to the sun

3I/ATLAS’s path (Teal line) is expected to take it relatively close to Earth on December 17. Scientists believe the object comes from a source outside our solar system

In a blog post this week, Loeb explained that a precursor probe smaller than 330 feet (100 meters) would not be detected by human telescopes due to their limited ability to capture reflected sunlight. 

Loeb’s calculations showed that if this probe exists, it could reach Mars around the same time as 3I/ATLAS’s closest approach, possibly a week earlier in late September.

The Frank B Baird Jr Professor of Science added that if 3I/ATLAS was a natural comet, any pieces breaking off it wouldn’t have enough speed to travel the huge distance to Mars.

Also, the cloud of gas and dust around 3I/ATLAS, observed by a telescope called SPHEREx, isn’t big enough to reach Mars on its own.

So, if anything from 3I/ATLAS does reach Mars, Loeb argued it would suggest the object is artificial, like a spacecraft or probe, rather than a natural object.

It would take only a small orbit correction, a tweak in the object’s speed and direction using thrusters or an engine, of about 6.2 to 9.3 miles per second this month to put the mini-probe on a collision course with Mars, the scientist explained in his blog on Medium.

Relatively speaking, that’s nothing for 3I/ATLAS, which has been barreling through our solar system at nearly 40 miles per second, or more than 140,000 miles per hour.

3I/ATLAS is also expected to make close passes by Venus and Jupiter this year. It’ll make its closest approach to Earth on December 17, when it’ll be within 223 million miles of our planet.

Avi Loeb has remained adamant that something about 3I/ATLAS does not add up. His new theory suggests that it may be a ship being accompanied by a small probe

The interstellar object known as 3I/ATLAS is now believed to be a unique comet that’s releasing tons of carbon dioxide gas

This isn’t the first extraordinary theory Loeb has had about the interstellar comet this year.

The astrophysicist has publicly discussed the possibility that 3I/ATLAS could be a giant, nuclear-powered vessel.

The shocking claim came after the Hubble Space Telescope took a picture of 3I/ATLAS on July 21 which appeared to show the object generating its own light.

Until then, the prevailing theory was that the fast-moving object was an ordinary comet approximately 12 miles long.

However, recent scans of 3I/ATLAS have detected about 940 trillion molecules of CO2 pouring out it per second, suggesting the mystery object really is a comet that formed in a star system that doesn’t look anything like ours.

NASA’s most powerful telescopes also cut the estimate of the object’s size down to 1.7 miles.

The comet seemed larger because over 99 percent of the light observed came from a large, bright cloud of dust and gas surrounding it, called a coma.

Loeb had previously claimed that 3I/ATLAS did not have a coma, stating that the object couldn’t be a comet as we know it without this cloud.