Kepler-738 b
Astrophysical Synthesis & Habitability Characterization
Kepler-738 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-738, located approximately 3632.2 light-years (1113.65 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0781% across the stellar disk), this world measures 2.5 Earth radii and has a measured mass of 6.8 Earth masses. Combining its mass and radius yields a mean bulk density of 2.4 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.4 km/s.
In its orbital architecture around Kepler-738, Kepler-738 b completes one full revolution every 24.587 Earth days at a semi-major axis of 0.1552 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 68.7 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 530 K (+257°C / +495°F) and receiving 27.64 S⊕ (~37,623 W/m²), Kepler-738 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-738 is classified as a stellar host with an effective photospheric temperature of 5,327 K, a radius of 0.82 R☉, a mass of 0.86 M☉, an estimated bolometric luminosity of 0.486 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.57 Gyr and a metallicity of [Fe/H] = -0.09 dex (near-solar heavy-element abundance). From Earth, Kepler-738 shines at apparent V-band magnitude 15.793 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-738 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,327 K |
| Stellar Radius | 0.8200 R☉ |
| Stellar Mass | 0.8600 M☉ |
| Bolometric Luminosity | 0.486 L☉ |
| Metallicity [Fe/H] | -0.090 dex |
| Stellar Age | 4.570 Gyr |
| Apparent Magnitude | V: 15.793 · G: 15.591 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.155200 AU |
| Orbital Period | 24.587 days |
| Mean Orbital Velocity | 68.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.0200° |
| Mean Bulk Density | 2.4 g/cm³ (18.4 km/s vesc) |
| Insolation Flux | 27.6440 S⊕ (~37,623 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3632.200 LY (1113.650 pc) |