Barnard b
Astrophysical Synthesis & Habitability Characterization
Barnard b 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 2024 by Paranal Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 0.72 Earth radii and has a measured mass of 0.299 Earth masses. Combining its mass and radius yields a mean bulk density of 4.42 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.58 g⊕ (5.69 m/s²), and an escape velocity of 7.2 km/s.
In its orbital architecture around Barnard's star, Barnard b completes one full revolution every 3.154 Earth days at a semi-major axis of 0.0229 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 79 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.03 (ranging from 0.0222 AU at periapsis to 0.0236 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 438 K (+165°C / +329°F) and receiving 6.76 S⊕ (~9,200 W/m²), Barnard b 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 b sharing its stellar neighborhood alongside Barnard d, Barnard c, 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: Paranal 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) | 0.022900 AU |
| Orbital Period | 3.154 days |
| Mean Orbital Velocity | 79 km/s |
| Orbital Eccentricity (e) | 0.03000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 4.42 g/cm³ (7.2 km/s vesc) |
| Insolation Flux | 6.7600 S⊕ (~9,200 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 6.000 LY (1.827 pc) |