Could an eighth planet be hiding within the TRAPPIST-1 system?

Space · Published 23 October 2026 Swipe more like this →

In short: We have long studied the seven rocky worlds orbiting TRAPPIST-1, a nearby star system famous for its Earth-sized planets. But recent hints suggest our map of this iconic system might be incomplete. Is there a hidden eighth world waiting to be discovered?

Located approximately 40 light-years from our Sun, the TRAPPIST-1 system is one of the most thoroughly studied planetary systems outside our own. Since the star's discovery in 1999, astronomers have identified seven terrestrial-sized planets, all of which were found using the transit method—detecting the slight dip in brightness as a planet passes in front of its host star. This method allows researchers to measure the radius and mass of these worlds, providing a window into their average density.

The composition of these seven planets is remarkably uniform. Recent calculations from EU-backed researchers, including those from the ESCAPE and BEBCO projects, show that the planets share similar ratios of iron, magnesium, and silicon. Nevertheless, a significant disparity exists compared to Earth; the density of the TRAPPIST-1 worlds is roughly 8% lower than expected if their composition matched our own. One theory suggests this is due to a lower iron content—21% compared to Earth's 32%—which could mean these worlds lack the strong magnetic fields necessary to protect atmospheres from solar particles.

While the known planets include several in the habitable zone, such as TRAPPIST-1 e, d, and f, the possibility of an eighth planet remains a subject of intrigue. While the current seven planets are all known to transit, the search for new members of this compact system continues. As we refine our data using tools like the James Webb Space Telescope, we may yet find that the 'most Earth-sized' batch of planets is even larger than we thought.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Seven Earth-sized worlds orbit a star smaller than Jupiter
• Seven Earth-sized planets discovered around a single ultra-cool dwarf star
• Seven rocky worlds orbit a tiny star just 40 light-years away
• Beyond the search for life: exploring the seven worlds of TRAPPIST-1
• Seven Earth-sized worlds orbit a single, tiny star
• Webb finds a rocky world nearly identical to Earth's size
• Could one of our neighbors be a binary planet system?
• A cosmic lottery? TRAPPIST-1d lacks an Earth-like atmosphere
• The planet that rewrote the rules of how solar systems form
• The Super-Earth that challenges our definition of a second home
• The first sign of alien life will likely be a sunset
• NASA's Kepler mission has identified 833 new candidate planets

More in Exoplanets · More in Space · Latest · A–Z · All topics