TRAPPIST-1 b
Reference profile for TRAPPIST-1 b: orbital period, planetary radius, dayside thermal emission from JWST, and transit parameters.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Distance | 40.66 ly | ± 0.04 ly | Trigonometric parallax of host star from Gaia DR3. | definitive | ESA Gaia Archive — Data Release 3 |
| Orbital Period | 1.51088 d | ± 0.00001 d | Multi-facility transit timing analysis (Agol et al. 2021). | definitive | NASA Exoplanet Archive |
| Semi-Major Axis | 0.01154 AU | ± 0.0001 AU | Keplerian third-law solution from stellar mass and orbital period | definitive | NASA Exoplanet Archive |
| Planetary Mass | 1.374 M⊕ | ± 0.069 M⊕ | Derived via photodynamical transit-timing variations. | high-confidence | NASA Exoplanet Archive |
| Planetary Radius | 1.116 R⊕ | ± 0.014 R⊕ | Transit depth photometry combined with Gaia stellar radius | definitive | NASA Exoplanet Archive |
| Equilibrium Temperature | 400 K | ± 8 K | Zero-albedo equilibrium estimate; JWST MIRI dayside brightness is ~503 K. | high-confidence | NASA Exoplanet Archive |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots TRAPPIST-1 b — Innermost Rocky World Data at RA 23h 06m 29.38s, Dec -05° 02′ 28.5″ within Aquarius, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Skimming just 1.73 million kilometers from its M8V host star, TRAPPIST-1 b occupies the innermost slot of a tightly packed seven-planet resonant chain. It completes a full circuit every 36.26 hours, moving in a near-circular path maintained alongside its siblings through an intricate 8:5 orbital period ratio with planet c. Because tidal torques at this proximity act over geological timescales far shorter than the system's multi-billion-year age, the planet is expected to be synchronously locked with a permanent dayside.
Photodynamical modeling of hundreds of transit timings reveals a radius of 1.116 Earth radii and a mass of 1.374 Earth masses, yielding a bulk density slightly below that of an uncompressed silicate-iron rock of identical size. Secondary eclipse photometry captured at 15 microns by the James Webb Space Telescope's Mid-Infrared Instrument measured a dayside brightness temperature near 503 K. This high thermal flux closely matches a dark, bare rock surface with negligible atmospheric heat redistribution to the nightside.
First identified in 2016 using the Transiting Planets and Planetesimals Small Telescope at La Silla Observatory, this world exhibits transit depths of roughly 0.73 percent against its diminutive ultracool dwarf host. In optical light, the parent star shines at an exceedingly faint V magnitude near 18.8, placing direct transit monitoring beyond small backyard telescopes, though professional infrared observatories routinely track its frequent 36-minute crossings.
Practical Visual Observing Guide
- Host star shines at V ~ 18.80 in Aquarius, though its infrared brightness (K ~ 10.3) makes it an ideal target for space-based infrared spectrophotometry.
- Transits recur every 1.51 days with a duration of 36 minutes and a depth of ~7,260 ppm.
- JWST MIRI 15-micron secondary eclipse observations rule out a thick carbon-dioxide-rich atmosphere.
Catalog Cross-Identifications & Aliases
Common Aliases: TRAPPIST-1b · 2MASS J23062928-0502285 b
| Catalog Authority | Identifier |
|---|---|
| NASAEXOPLANET | TRAPPIST-1 b |
| SIMBAD | TRAPPIST-1 b |
Related Objects, Comparisons & Guides
TRAPPIST-1 c — Warm Terrestrial Planet Data
Reference profile for TRAPPIST-1 c: mass, radius, orbital resonance, and JWST 15-micron atmospheric constraints.
TRAPPIST-1 e (Temperate Terrestrial World)
Coordinates, Gaia distance (12.47 pc), 6.10-day orbital period, mass 0.692 M⊕, radius 0.920 R⊕, and JWST transit spectroscopy for TRAPPIST-1 e.
Proxima Centauri b (Nearest Exoplanet)
Coordinates, ESPRESSO minimum mass (1.07 M⊕), 11.186-day habitable-zone orbit at 0.04856 AU, and stellar flare environment of Proxima Centauri b.
Exoplanet Transit & Radial Velocity Methods
How astronomers detect and characterize exoplanets using photometric transit depth ((Rp/R*)²), Doppler radial velocity (M sin i), and JWST transmission spectra.
Measurement Uncertainty & Optics in Astronomy
How random vs systematic errors, asymmetric error bars, model dependencies, and optical aperture/exit-pupil limits shape astronomical measurements.
Scientific Sources & Dataset Provenance
- NASA Exoplanet Archive (2026-10-01 snapshot): Akeson, R. L., et al. 2013, PASP, 125, 989; NASA Exoplanet Archive (IPAC/Caltech) — NASA Exoplanet Science Institute (NExScI / Caltech / IPAC)
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC