TRAPPIST-1 d
Reference data for TRAPPIST-1 d: sub-Earth mass and radius, 4.05-day period, insolation near the runaway greenhouse boundary, and TTV metrics.
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 | 4.04921 d | ± 0.00003 d | Multi-epoch transit or astrometric orbital fitting | definitive | NASA Exoplanet Archive |
| Semi-Major Axis | 0.02227 AU | ± 0.00019 AU | Keplerian third-law solution from stellar mass and orbital period | definitive | NASA Exoplanet Archive |
| Planetary Mass | 0.388 M⊕ | ± 0.012 M⊕ | Radial velocity or photodynamical transit-timing variations | high-confidence | NASA Exoplanet Archive |
| Planetary Radius | 0.788 R⊕ | ± 0.01 R⊕ | Transit depth photometry combined with Gaia stellar radius | definitive | NASA Exoplanet Archive |
| Equilibrium Temperature | 288 K | ± 6 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 d — Sub-Earth Exoplanet Profile 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
Spanning just 0.788 Earth radii and weighing 0.388 Earth masses, TRAPPIST-1 d is the smallest and least massive planet in its seven-world family, occupying a physical regime intermediate between Mars and Earth. It orbits at 0.0223 astronomical units in 4.049 days, locked in a 5:3 period commensurability with planet c inside it and a 3:2 commensurability with planet e outside it. Because of its small cross-section, its transit depth is roughly 0.37 percent, barely half that of the inner pair.
Receiving approximately 1.14 times Earth's incident stellar flux, this sub-Earth straddles the inner boundary of the conservative habitable zone. Three-dimensional general circulation models indicate that whether liquid water could persist on its surface depends critically on cloud feedback above the substellar point and the efficiency of tidal heating within its mantle. Its comparatively low uncompressed density suggests either a depleted iron core or a modest volatile inventory of water ice and hydrated minerals.
Initial ground-based observations in early 2016 captured only two partial transits of this third world, leaving its true period ambiguous between several aliases. Continuous photometric monitoring with the Spitzer Space Telescope later that year resolved the 4.05-day cadence unambiguously and revealed the gravitational tugs of its outer siblings through pronounced transit timing variations.
Practical Visual Observing Guide
- Produces a 49-minute transit every 4.05 days with a shallow ~3,670 ppm photometric dip.
- Exhibits substantial transit timing variations driven by the 3:2 mean-motion resonance with TRAPPIST-1 e.
- Requires space telescopes or large-aperture infrared facilities for transmission spectroscopy.
Catalog Cross-Identifications & Aliases
Common Aliases: TRAPPIST-1d · 2MASS J23062928-0502285 d
| Catalog Authority | Identifier |
|---|---|
| NASAEXOPLANET | TRAPPIST-1 d |
| SIMBAD | TRAPPIST-1 d |
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.
TRAPPIST-1 f — Cool Habitable-Zone Exoplanet
Reference data for TRAPPIST-1 f: Earth-twin radius, 9.21-day resonant orbit, volatile-rich interior models, and equilibrium temperature.
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