Ross 128 b
Astrophysical Synthesis & Habitability Characterization
Ross 128 b is a confirmed terrestrial exoplanet orbiting the star Ross 128, located approximately 11 light-years (3.38 parsecs) from the Solar System. First announced in 2017 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 1.11 Earth radii and has a measured mass of 1.4 Earth masses. Combining its mass and radius yields a mean bulk density of 5.64 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.14 g⊕ (11.18 m/s²), and an escape velocity of 12.6 km/s.
In its orbital architecture around Ross 128, Ross 128 b completes one full revolution every 9.866 Earth days at a semi-major axis of 0.0496 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 54.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.116 carries the world between 0.0438 AU at periapsis and 0.0554 AU at apoapsis, driving measurable seasonal insolation cycles.
✓ Classified as a Temperate Habitable Zone Candidate.
With an estimated equilibrium temperature of 301 K (+28°C / +82°F) and an incident stellar irradiance of 1.38 S⊕ (~1,878 W/m²), Ross 128 b orbits within the empirical circumstellar habitable zone where a rocky surface under sufficient atmospheric pressure can maintain liquid surface water.
The host star Ross 128 is classified as a low-mass red dwarf of spectral type M4 with an effective photospheric temperature of 3,192 K, a radius of 0.1967 R☉, a mass of 0.168 M☉, an estimated bolometric luminosity of 0.00360 L☉. Stellar evolution modeling indicates an estimated stellar age of 5 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, Ross 128 shines at apparent V-band magnitude 11.12 (faint and requiring research-grade or CCD telescopic photometry) 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Ross 128 |
| Spectral Type | M4 |
| Effective Temp (Teff) | 3,192 K |
| Stellar Radius | 0.1967 R☉ |
| Stellar Mass | 0.1680 M☉ |
| Bolometric Luminosity | 0.00360 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 5.000 Gyr |
| Apparent Magnitude | V: 11.120 · G: 9.591 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.049600 AU |
| Orbital Period | 9.866 days |
| Mean Orbital Velocity | 54.7 km/s |
| Orbital Eccentricity (e) | 0.11600 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 5.64 g/cm³ (12.6 km/s vesc) |
| Insolation Flux | 1.3800 S⊕ (~1,878 W/m²) |
| Habitable Zone Status | ★ Temperate Zone |
| Celestial Distance | 11.000 LY (3.375 pc) |