Kepler-303 b
Astrophysical Synthesis & Habitability Characterization
Kepler-303 b is a confirmed terrestrial exoplanet orbiting the star Kepler-303, located approximately 684.1 light-years (209.74 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0283% across the stellar disk), this world measures 0.89 Earth radii and has a measured mass of 0.64 Earth masses. Combining its mass and radius yields a mean bulk density of 5.01 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.81 g⊕ (7.94 m/s²), and an escape velocity of 9.5 km/s.
In its orbital architecture around Kepler-303, Kepler-303 b completes one full revolution every 1.937 Earth days at a semi-major axis of 0.024 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 134.8 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 802 K (+529°C / +984°F) and receiving 145.44 S⊕ (~197,938 W/m²), Kepler-303 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-303 is classified as a low-mass red dwarf of spectral type M0 V with an effective photospheric temperature of 3,944 K, a radius of 0.485 R☉, a mass of 0.575 M☉, an estimated bolometric luminosity of 0.051 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.71 Gyr and a metallicity of [Fe/H] = -0.414 dex (metal-poor relative to the Sun). From Earth, Kepler-303 shines at apparent V-band magnitude 14.917 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-303 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-303 b sharing its stellar neighborhood alongside Kepler-303 c.
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-303 |
| Spectral Type | M0 V |
| Effective Temp (Teff) | 3,944 K |
| Stellar Radius | 0.4850 R☉ |
| Stellar Mass | 0.5750 M☉ |
| Bolometric Luminosity | 0.051 L☉ |
| Metallicity [Fe/H] | -0.414 dex |
| Stellar Age | 7.710 Gyr |
| Apparent Magnitude | V: 14.917 · G: 14.396 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.024000 AU |
| Orbital Period | 1.937 days |
| Mean Orbital Velocity | 134.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.4100° |
| Mean Bulk Density | 5.01 g/cm³ (9.5 km/s vesc) |
| Insolation Flux | 145.4360 S⊕ (~197,938 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 684.100 LY (209.738 pc) |