pi Men d
Astrophysical Synthesis & Habitability Characterization
pi Men d is a confirmed sub-neptune exoplanet orbiting the star HD 39091, located approximately 59.6 light-years (18.27 parsecs) from the Solar System. First announced in 2022 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.72 Earth radii (0.33 Jupiter radii) and has a measured mass of 13.38 Earth masses. Combining its mass and radius yields a mean bulk density of 1.43 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.97 g⊕ (9.51 m/s²), and an escape velocity of 21.2 km/s.
In its orbital architecture around HD 39091, pi Men d completes one full revolution every 124.64 Earth days at a semi-major axis of 0.506 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 44.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.22 carries the world between 0.3947 AU at periapsis and 0.6173 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 444 K (+171°C / +340°F) and receiving 5.64 S⊕ (~7,676 W/m²), pi Men d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 39091 is classified as a solar-type yellow star of spectral type G0 V with an effective photospheric temperature of 5,998 K, a radius of 1.19 R☉, a mass of 1.07 M☉, an estimated bolometric luminosity of 1.644 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.92 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, HD 39091 shines at apparent V-band magnitude 5.65 (visible to the unaided human eye under dark skies) in the Southern celestial hemisphere. The HD 39091 system is a multi-planet architecture hosting 3 confirmed worlds, with pi Men d sharing its stellar neighborhood alongside pi Men c, HD 39091 b.
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 39091 |
| Spectral Type | G0 V |
| Effective Temp (Teff) | 5,998 K |
| Stellar Radius | 1.1900 R☉ |
| Stellar Mass | 1.0700 M☉ |
| Bolometric Luminosity | 1.644 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 3.920 Gyr |
| Apparent Magnitude | V: 5.650 · G: 5.513 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.506000 AU |
| Orbital Period | 124.64 days |
| Mean Orbital Velocity | 44.2 km/s |
| Orbital Eccentricity (e) | 0.22000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.43 g/cm³ (21.2 km/s vesc) |
| Insolation Flux | 5.6398 S⊕ (~7,676 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 59.600 LY (18.270 pc) |