Seven Earth-sized worlds orbit a star smaller than Jupiter

Space · Published 23 October 2026 Swipe more like this →

In short: The TRAPPIST-1 system is one of the most scrutinized planetary neighborhoods in the cosmos. Located just 40 light-years away, it hosts seven rocky planets packed into a compact orbit so tight that every world sits closer to its star than Mercury does to our Sun.

The TRAPPIST-1 system serves as a premier laboratory for exoplanetary science because of its unique geometry. The host star is an ultra-cool red dwarf, measuring only about 12 percent of the Sun's radius. Because the star is so small, the Earth-sized planets cover a larger fraction of its surface during a transit, making it significantly easier for instruments like the James Webb Space Telescope (JWST) to detect and analyze them.

While the planets are rocky and Earth-sized, their environment is extreme. The orbital periods are incredibly short, ranging from 1.5 to roughly 19 days. This proximity means that while three of the planets—e, f, and g—reside in the habitable zone where liquid water could theoretically exist, they are subject to intense stellar activity from the red dwarf. This activity complicates the interpretation of atmospheric data, as it can strip away gases or create complex chemical signatures.

JWST is currently using transmission spectroscopy to peer into these atmospheres, moving beyond the limits of the Hubble and Spitzer telescopes. The findings so far are a mixed bag: Planet b is a scorched, airless world, while Planet c is the coldest rocky exoplanet ever measured. Meanwhile, Planet e remains a primary candidate for Earth-like conditions, and Planet f is a potential steam-world. While life is not yet confirmed, the system remains a cornerstone of the search for habitable worlds.

The ultimate goal is to determine if these planets can retain atmospheres. Previous Hubble observations ruled out puffy, hydrogen-rich atmospheres similar to Neptune's for some planets, but JWST is now providing the high-resolution data needed to see what remains. The verdict is still unfolding, but the system offers a rare opportunity to study a compact, multi-planet architecture in our own galactic backyard.

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