TRAPPIST-1 h
TRAPPIST-1 h is a terrestrial planet orbiting TRAPPIST-1 in the constellation Aquarius. It was discovered in 2017 using the transit method.
How Big Is TRAPPIST-1 h?
TRAPPIST-1 h has a radius of 0.76 times that of Earth. Its mass is 0.33 times that of Earth, giving it a density of 4.16 g/cm³ — between that of rocky and gaseous planets.
Is TRAPPIST-1 h in the Habitable Zone?
TRAPPIST-1 h orbits beyond the outer edge of the habitable zone of TRAPPIST-1. At that distance, any surface water would almost certainly be frozen.
Habitable zone of TRAPPIST-1: 0.019–0.053 AU (conservative: 0.025–0.050 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Temperature on TRAPPIST-1 h
TRAPPIST-1 h receives 0.14 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TRAPPIST-1 h — one full orbit around TRAPPIST-1 — lasts 18.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.062 AU — closer to its star than Mercury is to the Sun.
How Was TRAPPIST-1 h Discovered?
TRAPPIST-1 h was discovered in 2017 using the transit method, with observations from Multiple Observatories.
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. TRAPPIST-1 h scores 0.46, ranking #305 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TRAPPIST-1
TRAPPIST-1
- Surface temperature
- 2,566 K (Sun: 5,772 K)
- Mass
- 0.09 M☉
- Radius
- 0.12 R☉
- Luminosity
- 0.0006 L☉
The TRAPPIST-1 Planetary System
TRAPPIST-1 h is one of 7 known planets in the TRAPPIST-1 system. Its siblings:
- TRAPPIST-1 b (Terrestrial)
- TRAPPIST-1 c (Terrestrial)
- TRAPPIST-1 d (Terrestrial)
- TRAPPIST-1 e (Terrestrial)
- TRAPPIST-1 f (Terrestrial)
- TRAPPIST-1 g (Terrestrial)
TRAPPIST-1 h — Complete Data
| Radius | 0.755 Earth radii (0.067 Jupiter radii) |
|---|---|
| Mass | 0.33 Earth masses (0.001 Jupiter masses) |
| Density | 4.16 g/cm³ (Earth: 5.51) |
| Orbital period | 18.77 days |
| Orbital distance | 0.062 AU |
| Stellar irradiation | 0.14× Earth |
| Earth Similarity Index | 0.46 |
| Constellation | Aquarius |
| Discovery method | Transit |
| Discovery facility | Multiple Observatories |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2022-11-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TRAPPIST-1 h
Is TRAPPIST-1 h habitable?
No — TRAPPIST-1 h orbits outside the habitable zone of TRAPPIST-1 and is likely too cold for liquid water on its surface.
How big is TRAPPIST-1 h compared to Earth?
TRAPPIST-1 h has 0.76 times the radius of Earth and about 0.33 times its mass.
How long is a year on TRAPPIST-1 h?
One orbit around TRAPPIST-1 takes 18.8 Earth days — short enough that 19 of its years would fit into one Earth year.
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