Comet 3I/ATLAS's Acceleration Might Not Be Caused By Gravity

The first reports of comet 3I/ATLAS were made on July 1, 2025, by the ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope in Chile. This comet caught the world's attention since it was the third interstellar visitor to the solar system in recorded history. Lately, it's been generating buzz for seeming to accelerate quickly near the sun, emitting a distinctive blue color, leading some to speculate it is an alien spacecraft lighting up its engines. There may be another explanation that is less science fiction, but no less interesting.

The leading theory is that its acceleration is not caused by alien antimatter drives, but instead by it losing mass. Simply put, as it loses mass it gets a burst of speed. The mass it loses creates a plume behind it, the same effect that some think is an alien engine at work. Though we know the likely source of its non-gravitational acceleration, 3I/ATLAS is still a bit of a mystery, deviating from what is normally seen in comets. 

Comet 3I/ATLAS will get within about 170 million miles from Earth, but that's the closest it will come (it is not a threat like dark comets are). It made its closest approach to the sun on October 30, and should reappear on the other side of the sun in early December 2025. Though it is hard to get an exact size, NASA estimates it to be between 1,444 feet and 3.5 miles in diameter.

The comet's non-gravitational acceleration suggests it is being pushed by something else, such as gas blasting off its surface as it heats up. If that's the case, the comet should be shedding mass fast enough to create a big cloud of material around it. When it emerges from the other side of the sun, astronomers may get a clear enough look to see if that is the case.

Comet 3I/ATLAS has also been getting brighter much faster than normal comets do. This does support the theory of heavy evaporation driven by sunlight. Still, it has been turning bluer than the sun, something completely unexpected for an object that should reflect redder light. One theory is that the unusual color comes from ionized gas. Of course, the color has also sparked theories of internal engines.

Despite the surprising acceleration, its course is still following a predictable route and won't put Earth in any danger from the comet. The behavior of this comet has certainly drawn the attention of the scientific community. Since it is only the third interstellar object to pass through our solar system, it presents a great opportunity for discovery.

One of the weirdest quirks of 3I/ATLAS is that it has surprisingly high levels of carbon dioxide. In fact, its CO₂-to-H₂O ratio is 8:1, which is one of the highest that's been recorded. Note, though, that ice in comets isn't much like water on Earth. The theory is that the solar system it came from has high levels of carbon dioxide. So what is unique to us would be commonplace for this comet.

Speaking of where it came from, that is still a mystery. Thoughts are that it came from the Milky Way's bulge, the central hub of our galaxy with a diverse array of stars of various ages and orbital paths. It's also uncertain what caused it to leave its own home and end up in our solar system in the first place. It likely was some type of unusual gravitational anomaly that messed up its orbital path.

Comet 3I/ATLAS reminds us that we know so very little about our own galaxy. It offers a unique chance to study something that is so markedly different from what we expect. As it continues to move through our solar system, we can learn a lot from its behavior and composition.