TRAPPIST-1 b
Planet· orbits TRAPPIST-1
TRAPPIST-1 b — the innermost planet, a hot rocky world on a 1.5-day orbit receiving about four times Earth's sunlight. Slightly larger and heavier than Earth, with an Earth-like density. In 2023 JWST measured its dayside and found it consistent with little or no atmosphere. Far too hot for habitability; its surface has never been imaged.
Open in 3D viewSee TRAPPIST-1 b in the live, interactive 3D map
Key facts
Mass
8.21 × 10²⁴ kg
1.37 M⊕
Radius
7,110 km
1.12× wider than Earth
Surface gravity
10.8 m/s²
1.1× Earth's gravity
Year
1.51 Earth days
Distance from TRAPPIST-1
1,726,359 km
Science
Physical
- Mass
- 8.21 × 10²⁴ kg · 1.37 M⊕
- Agol et al. 2021 — transit-timing variations
- Radius
- 7,110 km · 1.12× wider than Earth
- Agol et al. 2021 — transit photometry
- Density
- 5,450 kg/m³ · 5.5× water
- Computed from mass and radius
- Surface gravity
- 10.8 m/s² · 1.1× Earth's gravity
- Computed from mass and radius
- Escape velocity
- 12.4 km/s · 1.11× Earth's escape velocity
- Computed from mass and radius
Orbital
- Semi-major axis
- 1,726,359 km
- Real orbital elements (semi-major axis, period, eccentricity) from the NASA Exoplanet Archive; the system is shown face-on in the zone plane
- Eccentricity
- 0.00622
- Real orbital elements (semi-major axis, period, eccentricity) from the NASA Exoplanet Archive; the system is shown face-on in the zone plane
- Inclination
- 0.00 °
- Real orbital elements (semi-major axis, period, eccentricity) from the NASA Exoplanet Archive; the system is shown face-on in the zone plane
- Orbital period
- 36.26 hours
- Real orbital elements (semi-major axis, period, eccentricity) from the NASA Exoplanet Archive; the system is shown face-on in the zone plane
- Perihelion
- 1,715,621 km
- Computed from the orbital elements
- Aphelion
- 1,737,097 km
- Computed from the orbital elements
- Mean orbital velocity
- 83.1 km/s
- Computed from the orbital elements
Atmosphere
- Composition
- In 2023 JWST measured TRAPPIST-1 b's dayside and found it consistent with little or no atmosphere — a bare rock heated to roughly 230 °C. Far too hot and irradiated to be habitable; it receives about four times Earth's sunlight.
Composition
- Bulk composition
- Rocky. A measured mass of 1.37 Earth and radius 1.12 Earth give an Earth-like density, consistent with a rock-and-iron world. Its surface has never been imaged.
- Surface appearance
- Appearance based on NASA/ESA/CSA (JWST)'s artist's concept. No spacecraft has imaged this world, so its real appearance is unknown — The surface shown is an artistic representation, shown only in Visual mode; Realism shows a plain spectral colour.
Radiation & temperature
- Insolation
- 4.15 S⊕ · 4.15× the sunlight Earth receives
- Computed from TRAPPIST-1's luminosity and the orbital distance (inverse-square; Earth's sunlight = 1).
- Equilibrium temperature
- 398 K (125 °C)
- Computed model value (assumes no atmosphere), for the ~4× Earth's flux the planet receives on its 1.5-day orbit — not a measured temperature. In 2023 JWST measured its dayside heat directly and found it consistent with a bare rock and little or no atmosphere.
Discovery & history
- Discovered
- May 2, 2016
- By
- Michaël Gillon et al. (TRAPPIST / Spitzer)
- Method
- Transit detection
- Name
- Designated 'b' by its position in the system — planets are lettered inward to outward starting at 'b', so TRAPPIST-1 b is the innermost and h the outermost.
First detected in 2016 with the TRAPPIST telescope at ESO's La Silla Observatory (Gillon et al., Nature, May 2016) — among the first planets found transiting an ultracool dwarf star. Its size and orbit were pinned down the following year by NASA's Spitzer Space Telescope, which revealed the full seven-planet system.
Images
Images from open archives · credit shown per image