K2-278 b
Astrophysical Synthesis & Habitability Characterization
K2-278 b is a confirmed sub-neptune exoplanet orbiting the star K2-278, located approximately 2565 light-years (786.44 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0288% across the stellar disk), this world measures 2.98 Earth radii and has a measured mass of 9.17 Earth masses. Combining its mass and radius yields a mean bulk density of 1.91 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.03 g⊕ (10.1 m/s²), and an escape velocity of 19.6 km/s.
In its orbital architecture around K2-278, K2-278 b completes one full revolution every 3.335 Earth days at a semi-major axis of 0.0488 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 159.2 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1711 K (+1438°C / +2620°F) and receiving 1,051.56 S⊕ (~1,431,171 W/m²), K2-278 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-278 is classified as a stellar host with an effective photospheric temperature of 6,747 K, a radius of 1.61 R☉, a mass of 1.4 M☉, an estimated bolometric luminosity of 4.819 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, K2-278 shines at apparent V-band magnitude 13.446 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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 | K2-278 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,747 K |
| Stellar Radius | 1.6100 R☉ |
| Stellar Mass | 1.4000 M☉ |
| Bolometric Luminosity | 4.819 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.446 · G: 13.254 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.048800 AU |
| Orbital Period | 3.335 days |
| Mean Orbital Velocity | 159.2 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.91 g/cm³ (19.6 km/s vesc) |
| Insolation Flux | 1051.5587 S⊕ (~1,431,171 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2565.000 LY (786.439 pc) |