HD 158259 c
Astrophysical Synthesis & Habitability Characterization
HD 158259 c is a confirmed sub-neptune exoplanet orbiting the star HD 158259, located approximately 88.2 light-years (27.05 parsecs) from the Solar System. First announced in 2020 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.23 Earth radii and has a measured mass of 5.6 Earth masses. Combining its mass and radius yields a mean bulk density of 2.78 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 17.7 km/s.
In its orbital architecture around HD 158259, HD 158259 c completes one full revolution every 3.432 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.230 R⊕, HD 158259 c 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 158259 is classified as a solar-type yellow star of spectral type G0 with an effective photospheric temperature of 5,802 K, a radius of 1.21 R☉, a mass of 1.08 M☉, an estimated bolometric luminosity of 1.489 L☉. From Earth, HD 158259 shines at apparent V-band magnitude 6.479 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 158259 system is a multi-planet architecture hosting 5 confirmed worlds, with HD 158259 c sharing its stellar neighborhood alongside HD 158259 b, HD 158259 d, HD 158259 e, HD 158259 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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 158259 |
| Spectral Type | G0 |
| Effective Temp (Teff) | 5,802 K |
| Stellar Radius | 1.2100 R☉ |
| Stellar Mass | 1.0800 M☉ |
| Bolometric Luminosity | 1.489 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 6.479 · G: 6.307 |
| System Architecture | 1 Star, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 3.432 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.78 g/cm³ (17.7 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 88.200 LY (27.050 pc) |