Comet 3I/ATLAS will soon disappear behind the Sun, from our perspective on Earth, but before it does so, it will have a close encounter with the planet Mars, then with our own planet.
In fact, the comet will come so close to the Sun, it will actually pass within Mars's orbit – i.e. between Mars and the Sun – on its journey through our Solar System.
So what are the chances that 3I/ATLAS might hit Mars? Or we might even ask: will this strange rock from interstellar space hit Earth?
The story so far
Comet 3I/ATLAS was discovered on 1 July 2025 by astronomers using the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile.
It's an interstellar visitor, which distinguishes it from the vast majority of known comets that originate from within our Solar System and orbit the Sun.
3I/ATLAS originated from deep space, around a distant star, and is simply passing through our Solar System.
It won't go into orbit around our Sun; it has entered our Solar System and will eventually leave.
Since its discovery, some of the most powerful telescopes on Earth – and in space – have captured images of 3I/ATLAS, including the Very Large Telescope, the Gemini North telescope, SPHEREx and Webb, and the Hubble Space Telescope.
These observations have enabled scientists to pin down more detail about its size, its shape and what it's made of.
They've even been able to detect CO2 and water ice at the comet.
There's also evidence that it might be the oldest comet we've ever seen.
And astronomers have been able to calculate 3I/ATLAS's orbit, indicating its predicted path through our Solar System with remarkable accuracy.
3I/ATLAS and its close encounter with the planets
As you can see from the NASA diagram above, 3I/ATLAS will pass pretty close to the Sun, Earth, Mars and Jupiter on its way across our Solar System.
It will get pass by close to Earth, at least on a cosmic scale. Scientists estimate the closest it will get to our planet is about 270 million km (170 million miles).
That's about 1.8 astronomical units (AU), where 1 AU is the average distance between Earth and the Sun.
Considering the comet originated in deep space and could have been flung in any direction across the Universe, that's pretty close.
According to NOIRLab, operated by the U.S. National Science Foundation, 3I/ATLAS's close approach to Earth is due on 19 December 2025.
But before that, it will make its closest approach to the Sun around 30 October 2025, getting as close as 210 million km (130 million miles).
Again, given the vastness of the Universe, that's very close indeed.
At this point, it will be located between Mars's orbit and the Sun and travelling at 25,000 km (15,500 miles) per hour.
But even before that happens, 3I/ATLAS will make its closest approach to Mars on 3 October 2025, reaching a distance of just 28 million km (18 million miles) from the Red Planet.
That's about 0.19 AU, just a fifth of the distance between Earth and the Sun.
Will the comet hit Earth, Mars or Jupiter?
The short answer as to whether 3I/ATLAS will hit Earth, Mars or Jupiter is 'no'.
Scientists are able to pinpoint the orbits of celestial objects with remarkable accuracy by observing how these objects move through space.
Remember asteroid 2024 YR4, which was discovered in December 2024, and which made headlines because of the minuscule chance it might hit Earth or our Moon?
Astronomers were able to refine that object's orbit with each passing day, the small chance of it hitting our planet diminishing even further by the time it reached a distance where it could no longer be observed.
All evidence points to comet 3I/ATLAS passing through our Solar System without hitting any of the planets, including our own.
What's really interesting, however, is the prospect of some of the many robotic rovers and other spacecraft currently in our Solar System capturing a glimpse of 3I/ATLAS.
That would mean image showing the oldest comet we know of, which originated around a distant star, as seen from the perspective of another planet.
There's already talk of Mars missions like the European Space Agency's Mars Express and ExoMars Trace Gas Orbiter spacecraft carrying out observations of the comet, as reported by Space.com.
Or the HiRISE camera on NASA's Mars Reconnaissance Orbiter could be used to spy the comet, too.
And a paper submitted to Cornell University suggests that other spacecraft like "the Europa Clipper, Hera and even the more distant Lucy spacecraft may pass through 3I's cometary tail in the period after its perihelion passage, potentially directly observing the conditions and composition there."
It seems, then, that our best views of 3I/ATLAS, our best chances of gathering data on this interstellar visitor, may come not from telescopes on Earth or even in Earth orbit, but instead from telescopes and spacecraft we've put on other planets.
