Kepler-253 d
Astrophysical Synthesis & Habitability Characterization
Kepler-253 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-253, located approximately 2735.1 light-years (838.6 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1367% across the stellar disk), this world measures 3.17 Earth radii (0.28 Jupiter radii) and has a measured mass of 10.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.77 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 20.1 km/s.
In its orbital architecture around Kepler-253, Kepler-253 d completes one full revolution every 18.12 Earth days at a semi-major axis of 0.13 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 78.1 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 563 K (+290°C / +554°F) and receiving 24.08 S⊕ (~32,778 W/m²), Kepler-253 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-253 is classified as a stellar host with an effective photospheric temperature of 5,208 K, a radius of 0.786 R☉, a mass of 0.86 M☉, an estimated bolometric luminosity of 0.408 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.72 Gyr and a metallicity of [Fe/H] = 0.15 dex (metal-rich relative to the Sun). From Earth, Kepler-253 shines at apparent V-band magnitude 15.778 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-253 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-253 d sharing its stellar neighborhood alongside Kepler-253 b, Kepler-253 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-253 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,208 K |
| Stellar Radius | 0.7860 R☉ |
| Stellar Mass | 0.8600 M☉ |
| Bolometric Luminosity | 0.408 L☉ |
| Metallicity [Fe/H] | 0.150 dex |
| Stellar Age | 3.720 Gyr |
| Apparent Magnitude | V: 15.778 · G: 15.512 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.130000 AU |
| Orbital Period | 18.12 days |
| Mean Orbital Velocity | 78.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.6400° |
| Mean Bulk Density | 1.77 g/cm³ (20.1 km/s vesc) |
| Insolation Flux | 24.0840 S⊕ (~32,778 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2735.100 LY (838.595 pc) |