HD 31527 d
Astrophysical Synthesis & Habitability Characterization
HD 31527 d is a confirmed sub-neptune exoplanet orbiting the star HD 31527, located approximately 125.4 light-years (38.45 parsecs) from the Solar System. First announced in 2019 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.46 Earth radii (0.31 Jupiter radii) and has a measured mass of 11.82 Earth masses. Combining its mass and radius yields a mean bulk density of 1.57 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 20.7 km/s.
In its orbital architecture around HD 31527, HD 31527 d completes one full revolution every 271.674 Earth days at a semi-major axis of 0.8098 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 32.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.24 carries the world between 0.6154 AU at periapsis and 1.0042 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 3.460 R⊕, HD 31527 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 HD 31527 is classified as a solar-type yellow star of spectral type G2 V with an effective photospheric temperature of 5,898 K, a radius of 1.0737 R☉, a mass of 0.96 M☉, an estimated bolometric luminosity of 1.252 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.17 dex (metal-poor relative to the Sun). From Earth, HD 31527 shines at apparent V-band magnitude 7.49 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 31527 system is a multi-planet architecture hosting 3 confirmed worlds, with HD 31527 d sharing its stellar neighborhood alongside HD 31527 b, HD 31527 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 31527 |
| Spectral Type | G2 V |
| Effective Temp (Teff) | 5,898 K |
| Stellar Radius | 1.0737 R☉ |
| Stellar Mass | 0.9600 M☉ |
| Bolometric Luminosity | 1.252 L☉ |
| Metallicity [Fe/H] | -0.170 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 7.490 · G: 7.332 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.809800 AU |
| Orbital Period | 271.674 days |
| Mean Orbital Velocity | 32.4 km/s |
| Orbital Eccentricity (e) | 0.24000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.57 g/cm³ (20.7 km/s vesc) |
| Insolation Flux | 1.8299 S⊕ (~2,490 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 125.400 LY (38.447 pc) |