Kepler-37 d
Astrophysical Synthesis & Habitability Characterization
Kepler-37 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-37, located approximately 208.5 light-years (63.92 parsecs) from the Solar System. First announced in 2013 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0556% across the stellar disk), this world measures 2.03 Earth radii and has a measured mass of 2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.32 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.49 g⊕ (4.81 m/s²), and an escape velocity of 11.1 km/s.
In its orbital architecture around Kepler-37, Kepler-37 d completes one full revolution every 39.792 Earth days at a semi-major axis of 0.2109 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 57.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.1 carries the world between 0.1898 AU at periapsis and 0.232 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 499 K (+226°C / +439°F) and receiving 10.39 S⊕ (~14,141 W/m²), Kepler-37 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-37 is classified as a stellar host with an effective photospheric temperature of 5,357 K, a radius of 0.789 R☉, a mass of 0.79 M☉, an estimated bolometric luminosity of 0.46 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.6 Gyr and a metallicity of [Fe/H] = -0.36 dex (metal-poor relative to the Sun). From Earth, Kepler-37 shines at apparent V-band magnitude 9.77 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The Kepler-37 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-37 d sharing its stellar neighborhood alongside Kepler-37 b, Kepler-37 c, Kepler-37 e.
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-37 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,357 K |
| Stellar Radius | 0.7890 R☉ |
| Stellar Mass | 0.7900 M☉ |
| Bolometric Luminosity | 0.46 L☉ |
| Metallicity [Fe/H] | -0.360 dex |
| Stellar Age | 7.600 Gyr |
| Apparent Magnitude | V: 9.770 · G: 9.550 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.210900 AU |
| Orbital Period | 39.792 days |
| Mean Orbital Velocity | 57.7 km/s |
| Orbital Eccentricity (e) | 0.10000 |
| Orbital Inclination (i) | 89.3350° |
| Mean Bulk Density | 1.32 g/cm³ (11.1 km/s vesc) |
| Insolation Flux | 10.3900 S⊕ (~14,141 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 208.500 LY (63.921 pc) |