SPECULOOS-3 b
Astrophysical Synthesis & Habitability Characterization
SPECULOOS-3 b is a confirmed terrestrial exoplanet orbiting the star SPECULOOS-3. First announced in 2024 by SPECULOOS Southern Observatory using the Transit detection technique (producing an estimated primary transit depth of 0.5303% across the stellar disk), this world measures 0.977 Earth radii and has a measured mass of 0.894 Earth masses. Combining its mass and radius yields a mean bulk density of 5.29 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 10.7 km/s.
In its orbital architecture around SPECULOOS-3, SPECULOOS-3 b completes one full revolution every 0.719 Earth days at a semi-major axis of 0.00733 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 110.9 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 553 K (+280°C / +536°F) and receiving 15.54 S⊕ (~21,150 W/m²), SPECULOOS-3 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star SPECULOOS-3 is classified as a low-mass red dwarf of spectral type M6.5+/-0.5 with an effective photospheric temperature of 2,800 K, a radius of 0.123 R☉, a mass of 0.1009 M☉, an estimated bolometric luminosity of 0.00083 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.6 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, SPECULOOS-3 shines at apparent V-band magnitude 17.8 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: SPECULOOS Southern Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | SPECULOOS-3 |
| Spectral Type | M6.5+/-0.5 |
| Effective Temp (Teff) | 2,800 K |
| Stellar Radius | 0.1230 R☉ |
| Stellar Mass | 0.1009 M☉ |
| Bolometric Luminosity | 0.00083 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 6.600 Gyr |
| Apparent Magnitude | V: 17.800 · G: 15.402 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.007330 AU |
| Orbital Period | 0.719 days |
| Mean Orbital Velocity | 110.9 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.4400° |
| Mean Bulk Density | 5.29 g/cm³ (10.7 km/s vesc) |
| Insolation Flux | 15.5400 S⊕ (~21,150 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | — |