TRAPPIST-1 System Explained
TRAPPIST-1 is a laboratory rather than a curiosity: seven roughly Earth-size worlds orbit one small star, and their years last just a few Earth days. This diagram places them in orbital order with their sizes and the commonly discussed habitable-zone region.
Key takeaways
- All seven confirmed planets are close to Earth's size.
- Planets e, f and g are commonly placed in the habitable-zone range.
- The orbital chain is stabilised by a series of resonant period ratios.
- “In the habitable zone” is not the same as “confirmed habitable” or inhabited.
About this visual
TRAPPIST-1 is a small, cool "ultracool dwarf" star about 40 light-years from Earth. It hosts seven confirmed roughly Earth-size planets in a remarkably compact resonant chain. Read the full TRAPPIST-1 system article.
Orbital order and years
The planets are labelled b through h outward from the star. Because the star is so faint, all seven orbits fit inside what would be Mercury's orbit around the Sun. Their years last only 1.5 to 19 Earth days.
Habitable-zone context
Planets e, f and g sit in a commonly quoted habitable-zone range — the region where a rocky planet with a suitable atmosphere could hold liquid water on its surface. This is a starting point for study, not confirmation of habitability. Whether any TRAPPIST-1 planet has an atmosphere is the subject of intense JWST observations.
Why the resonant chain matters
TRAPPIST-1's planets have orbital periods close to small-integer ratios. Their mutual gravitational tugs produce transit-timing variations that let astronomers weigh the planets without a strong radial-velocity signal. The pattern also implies a smooth migration history — a planet formation record still visible today.
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Sources and methodology
Values verified against official mission and archive pages on the updated date shown above. Numeric quantities are cited to the precision typical of introductory astronomy references.