The comet 3I-ATLAS is big. Recent observations from the Vera C. Rubin Observatory show that it is nearly 11 kilometers wide, making it the largest interstellar object ever seen.
Scientists note that its composition is not fully mapped, but early spectra suggest a mix of water ice, carbon monoxide, methane, and organic-rich dust-materials typical of long-period comets. NASA researchers have pointed out that interstellar comets may carry exotic minerals not usually found in our solar system, which makes 3I-ATLAS an extraordinary natural sample of distant star systems.
Now imagine, just for a moment, that this giant comet does not pass Mars safely. Imagine it hits.
A collision of this size would release energy far greater than the asteroid impact that ended the dinosaurs on Earth. The surface of Mars would shake with global quakes, and the atmosphere would be filled with ejecta and dust that might linger for decades. More interesting is what comes with the comet. Water ice could melt and spread across crater basins, methane and carbon monoxide could enter the atmosphere, and organics could be delivered in large amounts.
Researchers already discuss how redirected comets might be used to terraform Mars. In this scenario, nature would do the job on its own. For decades, Mars could see a thicker atmosphere, more greenhouse warming, and perhaps even temporary liquid water. It would not make Mars immediately habitable for humans, but it could fast-forward the timeline of planetary engineering in unexpected ways.
NASA and ESA scientists stress that there is no chance of such a collision. The comet will pass at a safe distance of about 28 million kilometers from Mars in early October 2025. Still, the “what if” remains compelling because it touches on a deeper truth: comets carry the very stuff of life, and sometimes, the impact of one can change the destiny of a planet.
As Carl Sagan once said, “We are made of star stuff.” In 3I-ATLAS, humanity is watching that star stuff arrive from another sun.