The world’s 3rd known interstellar object – 3I/ATLAS – has made its closest approach to Mars. The approach took place at 4 UTC on October 3, 2025 (11 p.m. CDT on October 2). At that time, the comet was approximately 18 million miles (29 million kilometers) from Mars. It was the object’s closest approach to any planet during its one-time journey through our solar system.
As of this writing (10 UTC on October 3), we have not seen any new images from the pass. But multiple space agencies, including NASA and the European Space Agency (ESA), are coordinating observations using various spacecraft and orbiters around Mars. Instruments on ESA’s Mars Express and ExoMars Trace Gas Orbiter, as well as NASA’s Mars Reconnaissance Orbiter, are focusing on capturing detailed data from this interstellar visitor. In an October 2 story from AP, Marcia Dunn reported:
Both of the European Space Agency’s satellites around Mars are already aiming their cameras at the comet, which is only the 3rd interstellar object known to have passed our way. NASA’s satellite and rovers at the red planet are also available to assist in the observations.
Previously, Marshall Eubanks of Space Initiatives had said:
During the Mars close approach, the Mars Reconnaissance Orbiter will observe 3I with HiRISE, observing between 1 – 4 a.m. on October 2, and the CaSSIS camera on ESA’s Trace Gas Orbiter and the Mars Express’ High Resolution Stereo Camera will be observing on October 3.
3I/ATLAS will reach perihelion, its closest point to the sun, on October 29, 2025. Its perihelion distance will be roughly 1.36 astronomical units (AU) from the sun – just inside the orbit of Mars.
If you’re interested in tracking the object, NASA’s Eyes on the Solar System tool offers interactive simulations of its path. Also, NASA just launched a new page devoted to 3I/ATLAS. And the latest updates on ESA observations are here
Please note that 3I/ATLAS will not be visible to the unaided eye from Earth at this Mars approach, or at any time. It will be possible to view the object with 8-inch (20 cm) or larger telescopes … but the best time for that won’t come until November. If you spot it then, you’ll be in good company. Between November 2 and 25, ESA’s Jupiter Icy Moons Explorer (Juice) will be observing the comet with various instruments. As Juice looks towards 3I/ATLAS so soon after its closest approach to the sun, it is likely to have the best view of the comet in a very active state, with a bright halo around its nucleus and a long tail stretching out behind it.
Interstellar object 3I/ATLAS: A look backward
Where did 3I/ATLAS come from? We know it came from the Sagittarius direction in our sky; that is, it came from the direction of the center of our Milky Way galaxy. But there are billions of stars in that direction. Which one is the home system of this object?
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