Kepler-281 d
Astrophysical Synthesis & Habitability Characterization
Kepler-281 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-281, located approximately 5692.9 light-years (1745.45 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.3791% across the stellar disk), this world measures 5.937 Earth radii (0.53 Jupiter radii) and has a measured mass of 654 Earth masses (2.06 Jupiter masses). Combining its mass and radius yields a mean bulk density of 17.23 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 18.55 g⊕ (181.91 m/s²), and an escape velocity of 117.4 km/s.
In its orbital architecture around Kepler-281, Kepler-281 d completes one full revolution every 148.272 Earth days at a semi-major axis of 0.5456 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 40 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.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 5.937 R⊕, Kepler-281 d exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star Kepler-281 is classified as a stellar host with an effective photospheric temperature of 5,717 K, a radius of 0.884 R☉, a mass of 0.984 M☉, an estimated bolometric luminosity of 0.749 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.6 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, Kepler-281 shines at apparent V-band magnitude 15.931 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-281 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-281 d sharing its stellar neighborhood alongside Kepler-281 b, Kepler-281 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-281 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,717 K |
| Stellar Radius | 0.8840 R☉ |
| Stellar Mass | 0.9840 M☉ |
| Bolometric Luminosity | 0.749 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 0.600 Gyr |
| Apparent Magnitude | V: 15.931 · G: 15.754 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.545600 AU |
| Orbital Period | 148.272 days |
| Mean Orbital Velocity | 40 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.6600° |
| Mean Bulk Density | 17.23 g/cm³ (117.4 km/s vesc) |
| Insolation Flux | 2.5100 S⊕ (~3,416 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5692.900 LY (1745.450 pc) |