HIP 41378 d
Astrophysical Synthesis & Habitability Characterization
HIP 41378 d is a confirmed sub-neptune exoplanet orbiting the star HIP 41378, located approximately 346.7 light-years (106.29 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0663% across the stellar disk), this world measures 3.65 Earth radii (0.33 Jupiter radii) and has a measured mass of 6.53 Earth masses. Combining its mass and radius yields a mean bulk density of 0.74 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 15 km/s.
In its orbital architecture around HIP 41378, HIP 41378 d completes one full revolution every 278.362 Earth days at a semi-major axis of 1.17 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 45.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.063 carries the world between 1.0963 AU at periapsis and 1.2437 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 367 K (+94°C / +201°F) and receiving 3.01 S⊕ (~4,097 W/m²), HIP 41378 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HIP 41378 is classified as a warm F-type star of spectral type F6 with an effective photospheric temperature of 6,290 K, a radius of 1.3 R☉, a mass of 1.22 M☉, an estimated bolometric luminosity of 2.373 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.07 Gyr and a metallicity of [Fe/H] = -0.05 dex (near-solar heavy-element abundance). From Earth, HIP 41378 shines at apparent V-band magnitude 8.93 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HIP 41378 system is a multi-planet architecture hosting 6 confirmed worlds, with HIP 41378 d sharing its stellar neighborhood alongside HIP 41378 b, HIP 41378 c, HIP 41378 g, HIP 41378 e, HIP 41378 f.
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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HIP 41378 |
| Spectral Type | F6 |
| Effective Temp (Teff) | 6,290 K |
| Stellar Radius | 1.3000 R☉ |
| Stellar Mass | 1.2200 M☉ |
| Bolometric Luminosity | 2.373 L☉ |
| Metallicity [Fe/H] | -0.050 dex |
| Stellar Age | 2.070 Gyr |
| Apparent Magnitude | V: 8.930 · G: 8.810 |
| System Architecture | 1 Star, 6 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.170000 AU |
| Orbital Period | 278.362 days |
| Mean Orbital Velocity | 45.7 km/s |
| Orbital Eccentricity (e) | 0.06300 |
| Orbital Inclination (i) | 89.9300° |
| Mean Bulk Density | 0.74 g/cm³ (15 km/s vesc) |
| Insolation Flux | 3.0100 S⊕ (~4,097 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 346.700 LY (106.289 pc) |