There’s been a lot of hype and rumours about alien comet 3I/ATLAS lately, so where is it now, what did the spacecraft around Mars see when it passed by, when will it reappear in our skies, and is it really anything we need to worry about? Here’s the details.

Since its discovery back in early July, our latest visitor from interstellar space — 3I/2025 N1 (ATLAS), or 3I/ATLAS for short — has been speeding through the inner solar system at over 200,000 kilometres per hour, taking only three months to travel from just inside the orbit of Jupiter to sweeping past Mars at the beginning of October. For comparison, the fastest spacecraft ever launched from Earth, New Horizons, took more than 10 months — from April 7, 2006 to February 28, 2007 — to travel a similar distance.

The positions of comet 3I/ATLAS on July 1, when it was discovered, and October 3, when it made its closest pass by Mars. (NASA/JPL-Caltech/Scott Sutherland)

During the past three months, telescopes both on Earth and in space have been snapping images and collecting data about this galactic wanderer. After all, this object presents us with a unique opportunity, and for a limited time only.

We can’t journey to other planetary systems to explore them, but 3I/ATLAS was likely ejected from around some distant star. So, by studying its composition, we can get an idea of what the environment was like there, at least when the star and its planets were first forming. And, we only have until sometime next year to learn as much as we can from it, as it will pass outside of Jupiter’s orbit in March 2026, heading back towards interstellar space, after only a brief visit.

3I/ATLAS as seen by the Gemini South observatory on August 27, 2025. (International Gemini Observatory/NOIRLab/NSF/AURA/Shadow the Scientist. Image Processing: J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab), T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani (NSF NOIRLab))

Unfortunately, our observations of 3I/ATLAS currently have a bit of an interruption. In late September and through most of October, it is passing behind the Sun from our perspective. So, it’s not visible to any telescopes on Earth’s surface, and it’s actually dangerous to aim any of our space telescopes at it, as the intense light from the Sun can damage their optics.

3I/ATLAS at Mars

As luck would have it, though, on October 3 the comet passed just 30 million kilometres away from the only planet in the solar system, other than Earth, with multiple spacecraft orbiting around it, as well as more than one mission on the ground. And, as that happened, the space agencies that handle the majority of those missions — NASA and the ESA — were ready for it.