TRAPPIST-1 c
Reference profile for TRAPPIST-1 c: mass, radius, orbital resonance, and JWST 15-micron atmospheric constraints.
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 | Gaia DR3 trigonometric parallax of host star | definitive | ESA Gaia Archive — Data Release 3 |
| Orbital Period | 2.42193 d | ± 0.00002 d | Multi-epoch transit or astrometric orbital fitting | definitive | NASA Exoplanet Archive |
| Semi-Major Axis | 0.0158 AU | ± 0.00013 AU | Keplerian third-law solution from stellar mass and orbital period | definitive | NASA Exoplanet Archive |
| Planetary Mass | 1.308 M⊕ | ± 0.056 M⊕ | Radial velocity or photodynamical transit-timing variations | high-confidence | NASA Exoplanet Archive |
| Planetary Radius | 1.097 R⊕ | ± 0.014 R⊕ | Transit depth photometry combined with Gaia stellar radius | definitive | NASA Exoplanet Archive |
| Equilibrium Temperature | 342 K | ± 7 K | Radiative equilibrium calculation from bolometric stellar insolation | high-confidence | NASA Exoplanet Archive |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots TRAPPIST-1 c — Warm Terrestrial Planet 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
Positioned as the second planet outward from its red dwarf primary, TRAPPIST-1 c circles at a separation of 0.0158 astronomical units with an orbital period of 2.422 days. It participates in a three-body Laplace resonance linking planets b, c, and d, which continuously excites small orbital eccentricities and generates measurable transit timing shifts of several minutes. The world intercepts roughly 2.2 times the bolometric flux that Earth receives from the Sun, placing its radiative environment remarkably close to that of early Venus.
With a radius of 1.097 Earth radii and a mass of 1.308 Earth masses, the planet shares nearly the same bulk density as its inner neighbor, consistent with an iron core accounting for roughly one-fifth of its total mass beneath a silicate mantle. When observed during secondary eclipse at 15 microns, its dayside registered a brightness temperature of 380 ± 31 K. That measurement disfavors a dense, Venus-like carbon dioxide blanket and points instead toward either an airless regolith or a tenuous, low-pressure oxygen-dominated envelope.
Announced alongside planets b and d in May 2016 from ground-based near-infrared photometry, this world blocks approximately 0.70 percent of its host star's light during each 42-minute transit. Because intense stellar flares and coronal X-ray emission from the ultracool host have bombarded the inner system for billions of years, TRAPPIST-1 c serves as a premier benchmark for testing atmospheric escape physics around low-mass stars.
Practical Visual Observing Guide
- Transits last roughly 42 minutes and occur every 58.1 hours across the disk of its M8V host star.
- Secondary eclipse depth at 15 microns is approximately 420 ppm, measured via JWST MIRI photometry.
- Located in southern Aquarius; not accessible to visual amateur instruments.
Catalog Cross-Identifications & Aliases
Common Aliases: TRAPPIST-1c · 2MASS J23062928-0502285 c
| Catalog Authority | Identifier |
|---|---|
| NASAEXOPLANET | TRAPPIST-1 c |
| SIMBAD | TRAPPIST-1 c |
Related Objects, Comparisons & Guides
TRAPPIST-1 b — Innermost Rocky World Data
Reference profile for TRAPPIST-1 b: orbital period, planetary radius, dayside thermal emission from JWST, and transit parameters.
TRAPPIST-1 d — Sub-Earth Exoplanet Profile
Reference data for TRAPPIST-1 d: sub-Earth mass and radius, 4.05-day period, insolation near the runaway greenhouse boundary, and TTV metrics.
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.
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