Barnard c
Astrophysical Synthesis & Habitability Characterization
Barnard c is a confirmed sub-earth exoplanet orbiting the star Barnard's star, located approximately 6 light-years (1.83 parsecs) from the Solar System. First announced in 2025 by Gemini Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 0.743 Earth radii and has a measured mass of 0.335 Earth masses. Combining its mass and radius yields a mean bulk density of 4.5 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.61 g⊕ (5.98 m/s²), and an escape velocity of 7.5 km/s.
In its orbital architecture around Barnard's star, Barnard c completes one full revolution every 4.124 Earth days at a semi-major axis of 0.0274 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 72.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.08 carries the world between 0.0252 AU at periapsis and 0.0296 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 400 K (+127°C / +261°F) and receiving 4.73 S⊕ (~6,435 W/m²), Barnard c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Barnard's star is classified as a low-mass red dwarf of spectral type M3.5-4 V with an effective photospheric temperature of 3,195 K, a radius of 0.185 R☉, a mass of 0.162 M☉, an estimated bolometric luminosity of 0.00320 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.56 dex (metal-poor relative to the Sun). From Earth, Barnard's star shines at apparent V-band magnitude 9.54 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The Barnard's star system is a multi-planet architecture hosting 4 confirmed worlds, with Barnard c sharing its stellar neighborhood alongside Barnard d, Barnard b, Barnard e.
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: Gemini Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Barnard's star |
| Spectral Type | M3.5-4 V |
| Effective Temp (Teff) | 3,195 K |
| Stellar Radius | 0.1850 R☉ |
| Stellar Mass | 0.1620 M☉ |
| Bolometric Luminosity | 0.00320 L☉ |
| Metallicity [Fe/H] | -0.560 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.540 · G: 8.195 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.027400 AU |
| Orbital Period | 4.124 days |
| Mean Orbital Velocity | 72.3 km/s |
| Orbital Eccentricity (e) | 0.08000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 4.5 g/cm³ (7.5 km/s vesc) |
| Insolation Flux | 4.7285 S⊕ (~6,435 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 6.000 LY (1.827 pc) |