CoRoT-21 b
Astrophysical Synthesis & Habitability Characterization
CoRoT-21 b is a confirmed gas giant exoplanet orbiting the star CoRoT-21, located approximately 4562.4 light-years (1398.83 parsecs) from the Solar System. First announced in 2012 by CoRoT using the Transit detection technique (producing an estimated primary transit depth of 0.4694% across the stellar disk), this world measures 14.572 Earth radii (1.3 Jupiter radii) and has a measured mass of 718.296 Earth masses (2.26 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.28 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.38 g⊕ (33.15 m/s²), and an escape velocity of 78.5 km/s.
In its orbital architecture around CoRoT-21, CoRoT-21 b completes one full revolution every 2.725 Earth days at a semi-major axis of 0.0417 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 166.5 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 2044 K (+1771°C / +3220°F) and receiving 2,915.60 S⊕ (~3,968,131 W/m²), CoRoT-21 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star CoRoT-21 is classified as a warm F-type star of spectral type F8 IV with an effective photospheric temperature of 6,200 K, a radius of 1.95 R☉, a mass of 1.29 M☉, an estimated bolometric luminosity of 5.041 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.1 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, CoRoT-21 shines at apparent V-band magnitude 16.058 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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: CoRoT · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | CoRoT-21 |
| Spectral Type | F8 IV |
| Effective Temp (Teff) | 6,200 K |
| Stellar Radius | 1.9500 R☉ |
| Stellar Mass | 1.2900 M☉ |
| Bolometric Luminosity | 5.041 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 4.100 Gyr |
| Apparent Magnitude | V: 16.058 · G: 15.856 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.041700 AU |
| Orbital Period | 2.725 days |
| Mean Orbital Velocity | 166.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 86.8000° |
| Mean Bulk Density | 1.28 g/cm³ (78.5 km/s vesc) |
| Insolation Flux | 2915.5997 S⊕ (~3,968,131 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4562.400 LY (1398.834 pc) |