tau Cet g
Astrophysical Synthesis & Habitability Characterization
tau Cet g is a confirmed terrestrial exoplanet orbiting the star tau Cet, located approximately 11.8 light-years (3.6 parsecs) from the Solar System. First announced in 2017 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 1.18 Earth radii and has a measured mass of 1.75 Earth masses. Combining its mass and radius yields a mean bulk density of 5.87 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.26 g⊕ (12.36 m/s²), and an escape velocity of 13.6 km/s.
In its orbital architecture around tau Cet, tau Cet g completes one full revolution every 20 Earth days at a semi-major axis of 0.133 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 72.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.06 carries the world between 0.125 AU at periapsis and 0.141 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 640 K (+367°C / +693°F) and receiving 27.98 S⊕ (~38,086 W/m²), tau Cet g orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star tau Cet is classified as a solar-type yellow star of spectral type G8.5V with an effective photospheric temperature of 5,310 K, a radius of 0.83 R☉, a mass of 0.783 M☉, an estimated bolometric luminosity of 0.491 L☉. Stellar evolution modeling indicates an estimated stellar age of 12.12 Gyr and a metallicity of [Fe/H] = -0.52 dex (metal-poor relative to the Sun). From Earth, tau Cet shines at apparent V-band magnitude 3.496 (visible to the unaided human eye under dark skies) in the Southern celestial hemisphere. The tau Cet system is a multi-planet architecture hosting 3 confirmed worlds, with tau Cet g sharing its stellar neighborhood alongside tau Cet h, tau Cet f.
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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | tau Cet |
| Spectral Type | G8.5V |
| Effective Temp (Teff) | 5,310 K |
| Stellar Radius | 0.8300 R☉ |
| Stellar Mass | 0.7830 M☉ |
| Bolometric Luminosity | 0.491 L☉ |
| Metallicity [Fe/H] | -0.520 dex |
| Stellar Age | 12.120 Gyr |
| Apparent Magnitude | V: 3.496 · G: 3.249 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.133000 AU |
| Orbital Period | 20 days |
| Mean Orbital Velocity | 72.3 km/s |
| Orbital Eccentricity (e) | 0.06000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 5.87 g/cm³ (13.6 km/s vesc) |
| Insolation Flux | 27.9835 S⊕ (~38,086 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 11.800 LY (3.603 pc) |