Kepler-444 b
Astrophysical Synthesis & Habitability Characterization
Kepler-444 b is a confirmed sub-earth exoplanet orbiting the star Kepler-444, located approximately 118.8 light-years (36.44 parsecs) from the Solar System. First announced in 2015 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0024% across the stellar disk), this world measures 0.403 Earth radii and has a measured mass of 0.037 Earth masses. Combining its mass and radius yields a mean bulk density of 3.12 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 0.23 g⊕ (2.26 m/s²), and an escape velocity of 3.4 km/s.
In its orbital architecture around Kepler-444, Kepler-444 b completes one full revolution every 3.6 Earth days at a semi-major axis of 0.04178 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 126.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.16 carries the world between 0.0351 AU at periapsis and 0.0485 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 938 K (+665°C / +1229°F) and receiving 225.74 S⊕ (~307,225 W/m²), Kepler-444 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-444 is classified as an orange K-type star of spectral type K with an effective photospheric temperature of 5,046 K, a radius of 0.752 R☉, a mass of 0.758 M☉, an estimated bolometric luminosity of 0.329 L☉. Stellar evolution modeling indicates an estimated stellar age of 11.23 Gyr and a metallicity of [Fe/H] = -0.55 dex (metal-poor relative to the Sun). From Earth, Kepler-444 shines at apparent V-band magnitude 8.87 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The Kepler-444 system is a multi-planet architecture hosting 5 confirmed worlds, with Kepler-444 b sharing its stellar neighborhood alongside Kepler-444 c, Kepler-444 d, Kepler-444 e, Kepler-444 f.
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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-444 |
| Spectral Type | K |
| Effective Temp (Teff) | 5,046 K |
| Stellar Radius | 0.7520 R☉ |
| Stellar Mass | 0.7580 M☉ |
| Bolometric Luminosity | 0.329 L☉ |
| Metallicity [Fe/H] | -0.550 dex |
| Stellar Age | 11.230 Gyr |
| Apparent Magnitude | V: 8.870 · G: 8.643 |
| System Architecture | 3 Stars, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.041780 AU |
| Orbital Period | 3.6 days |
| Mean Orbital Velocity | 126.3 km/s |
| Orbital Eccentricity (e) | 0.16000 |
| Orbital Inclination (i) | 88.0000° |
| Mean Bulk Density | 3.12 g/cm³ (3.4 km/s vesc) |
| Insolation Flux | 225.7350 S⊕ (~307,225 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 118.800 LY (36.440 pc) |