Kepler-581 b
Astrophysical Synthesis & Habitability Characterization
Kepler-581 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-581, located approximately 2295.3 light-years (703.76 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0581% across the stellar disk), this world measures 2.63 Earth radii and has a measured mass of 7.41 Earth masses. Combining its mass and radius yields a mean bulk density of 2.25 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.07 g⊕ (10.49 m/s²), and an escape velocity of 18.8 km/s.
In its orbital architecture around Kepler-581, Kepler-581 b completes one full revolution every 40.607 Earth days at a semi-major axis of 0.2259 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 60.5 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 521 K (+248°C / +478°F) and receiving 12.39 S⊕ (~16,863 W/m²), Kepler-581 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-581 is classified as a stellar host with an effective photospheric temperature of 5,772 K, a radius of 1 R☉, a mass of 1 M☉, an estimated bolometric luminosity of 0.996 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.07 Gyr and a metallicity of [Fe/H] = 0.03 dex (near-solar heavy-element abundance). From Earth, Kepler-581 shines at apparent V-band magnitude 14.701 (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-581 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,772 K |
| Stellar Radius | 1.0000 R☉ |
| Stellar Mass | 1.0000 M☉ |
| Bolometric Luminosity | 0.996 L☉ |
| Metallicity [Fe/H] | 0.030 dex |
| Stellar Age | 4.070 Gyr |
| Apparent Magnitude | V: 14.701 · G: 14.530 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.225900 AU |
| Orbital Period | 40.607 days |
| Mean Orbital Velocity | 60.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.4100° |
| Mean Bulk Density | 2.25 g/cm³ (18.8 km/s vesc) |
| Insolation Flux | 12.3900 S⊕ (~16,863 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2295.300 LY (703.758 pc) |