Kepler-401 d
Astrophysical Synthesis & Habitability Characterization
Kepler-401 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-401, located approximately 3149.2 light-years (965.56 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.026% across the stellar disk), this world measures 2.27 Earth radii and has a measured mass of 5.77 Earth masses. Combining its mass and radius yields a mean bulk density of 2.72 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.8 km/s.
In its orbital architecture around Kepler-401, Kepler-401 d completes one full revolution every 184.256 Earth days at a semi-major axis of 0.66886 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 39.5 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 380 K (+107°C / +225°F) and receiving 8.49 S⊕ (~11,548 W/m²), Kepler-401 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-401 is classified as a stellar host with an effective photospheric temperature of 6,184 K, a radius of 1.29 R☉, a mass of 1.17 M☉, an estimated bolometric luminosity of 2.183 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.39 Gyr and a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, Kepler-401 shines at apparent V-band magnitude 13.366 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-401 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-401 d sharing its stellar neighborhood alongside Kepler-401 b, Kepler-401 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-401 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,184 K |
| Stellar Radius | 1.2900 R☉ |
| Stellar Mass | 1.1700 M☉ |
| Bolometric Luminosity | 2.183 L☉ |
| Metallicity [Fe/H] | 0.020 dex |
| Stellar Age | 3.390 Gyr |
| Apparent Magnitude | V: 13.366 · G: 13.287 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.668860 AU |
| Orbital Period | 184.256 days |
| Mean Orbital Velocity | 39.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.1500° |
| Mean Bulk Density | 2.72 g/cm³ (17.8 km/s vesc) |
| Insolation Flux | 8.4850 S⊕ (~11,548 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3149.200 LY (965.560 pc) |