K2-122 b
Astrophysical Synthesis & Habitability Characterization
K2-122 b is a confirmed terrestrial exoplanet orbiting the star K2-122, located approximately 235 light-years (72.04 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0325% across the stellar disk), this world measures 1.16 Earth radii and has a measured mass of 1.65 Earth masses. Combining its mass and radius yields a mean bulk density of 5.83 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.23 g⊕ (12.06 m/s²), and an escape velocity of 13.3 km/s.
In its orbital architecture around K2-122, K2-122 b completes one full revolution every 2.219 Earth days at a semi-major axis of 0.0373 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 182.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.21 carries the world between 0.0295 AU at periapsis and 0.0451 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 769 K (+496°C / +925°F) and receiving 79.90 S⊕ (~108,744 W/m²), K2-122 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-122 is classified as a low-mass red dwarf of spectral type M0 with an effective photospheric temperature of 4,009 K, a radius of 0.59 R☉, a mass of 0.63 M☉, an estimated bolometric luminosity of 0.081 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.32 dex (metal-rich relative to the Sun). From Earth, K2-122 shines at apparent V-band magnitude 13.105 (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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-122 |
| Spectral Type | M0 |
| Effective Temp (Teff) | 4,009 K |
| Stellar Radius | 0.5900 R☉ |
| Stellar Mass | 0.6300 M☉ |
| Bolometric Luminosity | 0.081 L☉ |
| Metallicity [Fe/H] | 0.320 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.105 · G: 12.371 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.037300 AU |
| Orbital Period | 2.219 days |
| Mean Orbital Velocity | 182.8 km/s |
| Orbital Eccentricity (e) | 0.21000 |
| Orbital Inclination (i) | 86.3900° |
| Mean Bulk Density | 5.83 g/cm³ (13.3 km/s vesc) |
| Insolation Flux | 79.9000 S⊕ (~108,744 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 235.000 LY (72.044 pc) |