The weird comet that may be planting planets around stars

A mysterious comet flying through our solar system may be doing more than just passing by-it could help explain how giant planets like Jupiter are born.

The comet, named 3I/ATLAS, is only the third confirmed interstellar object ever seen in our solar system. That means it came from another star system entirely. At first, some speculated it could be an alien spacecraft. But now, a new theory suggests something far more grounded-and just as fascinating.

At a major planetary science conference in Helsinki this week, German astrophysicist Susanne Pfalzner proposed that 3I/ATLAS, and other space rocks like it, might help kick-start the process of planet formation.

“Interstellar objects may be able to jump-start planet formation, in particular around higher-mass stars,” Pfalzner said in a statement.

Planets are thought to form in large disks of dust and gas that surround young stars. Over time, tiny particles in those disks bump into each other and slowly stick together, growing into larger and larger objects. But scientists have struggled to explain how these objects grow past a certain size. In computer models, anything bigger than a meter tends to crash and break apart instead of merging to form planets.

Pfalzner’s idea is that interstellar objects-solid bodies thrown out of other star systems-could act as building blocks, or “seeds,” that help speed up the process. Her computer models show that young stars could capture millions of these objects in their disks. Once inside, they could quickly gather more dust and gas, helping giant planets form before the disks disappear-which usually happens in just a few million years.

Her research also offers a possible reason why gas giants like Jupiter are more common around bigger stars than smaller ones. Larger stars are better at capturing these wandering interstellar visitors, which could explain why they end up with more giant planets.

3I/ATLAS fits right into this theory. It was discovered in the summer of 2025 and, like its interstellar cousins 1I/’Oumuamua and 2I/Borisov, follows a path that shows it isn’t from our solar system. It may be over seven billion years old-older than our Sun.

Recently, astronomers got an unusually clear look at 3I/ATLAS during the total lunar eclipse on Sept. 7. As the moon dimmed, the skies darkened, allowing photographers in Namibia to capture deep images of the comet. They showed something strange: a green glow.

That green color is usually caused by a molecule called diatomic carbon, which glows when exposed to sunlight. But earlier observations from a telescope in Arizona found that 3I/ATLAS is actually low in carbon-based molecules. That raises a new question-what’s causing the glow?

One idea is that sunlight has recently exposed new material beneath the comet’s surface. Another is that 3I/ATLAS contains unusual chemicals we haven’t seen in comets from our own solar system.

Pfalzner plans to keep testing her theory by running more simulations. She wants to know how many interstellar objects actually become planets, and whether they tend to gather in certain parts of the disk. For now, 3I/ATLAS is giving scientists a rare chance to study both how planets form and what strange materials might be arriving here from other worlds.

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