tau Gem b
Astrophysical Synthesis & Habitability Characterization
tau Gem b is a confirmed gas giant exoplanet orbiting the star tau Gem, located approximately 367 light-years (112.54 parsecs) from the Solar System. First announced in 2013 by Lick Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.1 Earth radii (1.08 Jupiter radii) and has a measured mass of 6547 Earth masses (20.6 Jupiter masses). Combining its mass and radius yields a mean bulk density of 20.38 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 44.72 g⊕ (438.55 m/s²), and an escape velocity of 260.2 km/s.
In its orbital architecture around tau Gem, tau Gem b completes one full revolution every 305.5 Earth days at a semi-major axis of 1.17 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 41.7 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.031 (ranging from 1.1337 AU at periapsis to 1.2063 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1013 K (+740°C / +1364°F) and receiving 241.31 S⊕ (~328,424 W/m²), tau Gem b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star tau Gem is classified as an orange K-type star of spectral type K2 III with an effective photospheric temperature of 4,388 K, a radius of 26.8 R☉, a mass of 2.3 M☉, an estimated bolometric luminosity of 238.905 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.22 Gyr and a metallicity of [Fe/H] = 0.14 dex (metal-rich relative to the Sun). From Earth, tau Gem shines at apparent V-band magnitude 4.378 (visible to the unaided human eye under dark skies) 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: Lick Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | tau Gem |
| Spectral Type | K2 III |
| Effective Temp (Teff) | 4,388 K |
| Stellar Radius | 26.8000 R☉ |
| Stellar Mass | 2.3000 M☉ |
| Bolometric Luminosity | 238.905 L☉ |
| Metallicity [Fe/H] | 0.140 dex |
| Stellar Age | 1.220 Gyr |
| Apparent Magnitude | V: 4.378 · G: 4.040 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.170000 AU |
| Orbital Period | 305.5 days |
| Mean Orbital Velocity | 41.7 km/s |
| Orbital Eccentricity (e) | 0.03100 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 20.38 g/cm³ (260.2 km/s vesc) |
| Insolation Flux | 241.3109 S⊕ (~328,424 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 367.000 LY (112.537 pc) |