HD 28471 d
Astrophysical Synthesis & Habitability Characterization
HD 28471 d is a confirmed sub-neptune exoplanet orbiting the star HD 28471, located approximately 142.4 light-years (43.65 parsecs) from the Solar System. First announced in 2025 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.06 Earth radii and has a measured mass of 4.91 Earth masses. Combining its mass and radius yields a mean bulk density of 3.1 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.16 g⊕ (11.38 m/s²), and an escape velocity of 17.3 km/s.
In its orbital architecture around HD 28471, HD 28471 d completes one full revolution every 11.681 Earth days at a semi-major axis of 0.1 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 93.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.093 carries the world between 0.0907 AU at periapsis and 0.1093 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 945 K (+672°C / +1242°F) and receiving 115.26 S⊕ (~156,867 W/m²), HD 28471 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 28471 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,766 K, a radius of 1.08 R☉, a mass of 0.98 M☉, an estimated bolometric luminosity of 1.157 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.56 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, HD 28471 shines at apparent V-band magnitude 7.89 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 28471 system is a multi-planet architecture hosting 3 confirmed worlds, with HD 28471 d sharing its stellar neighborhood alongside HD 28471 b, HD 28471 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 28471 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,766 K |
| Stellar Radius | 1.0800 R☉ |
| Stellar Mass | 0.9800 M☉ |
| Bolometric Luminosity | 1.157 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 6.560 Gyr |
| Apparent Magnitude | V: 7.890 · G: 7.728 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.100000 AU |
| Orbital Period | 11.681 days |
| Mean Orbital Velocity | 93.1 km/s |
| Orbital Eccentricity (e) | 0.09300 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 3.1 g/cm³ (17.3 km/s vesc) |
| Insolation Flux | 115.2590 S⊕ (~156,867 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 142.400 LY (43.646 pc) |