HD 5278 b
Astrophysical Synthesis & Habitability Characterization
HD 5278 b is a confirmed sub-neptune exoplanet orbiting the star HD 5278, located approximately 187.8 light-years (57.59 parsecs) from the Solar System. First announced in 2021 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0354% across the stellar disk), this world measures 2.45 Earth radii and has a measured mass of 7.8 Earth masses. Combining its mass and radius yields a mean bulk density of 2.92 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.3 g⊕ (12.75 m/s²), and an escape velocity of 20 km/s.
In its orbital architecture around HD 5278, HD 5278 b completes one full revolution every 14.339 Earth days at a semi-major axis of 0.1202 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 91.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.08 carries the world between 0.1106 AU at periapsis and 0.1298 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 943 K (+670°C / +1238°F) and receiving 132.00 S⊕ (~179,652 W/m²), HD 5278 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 5278 is classified as a warm F-type star of spectral type F V with an effective photospheric temperature of 6,203 K, a radius of 1.194 R☉, a mass of 1.126 M☉, an estimated bolometric luminosity of 1.894 L☉. Stellar evolution modeling indicates an estimated stellar age of 3 Gyr and a metallicity of [Fe/H] = -0.12 dex (metal-poor relative to the Sun). From Earth, HD 5278 shines at apparent V-band magnitude 7.94 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 5278 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 5278 b sharing its stellar neighborhood alongside HD 5278 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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 5278 |
| Spectral Type | F V |
| Effective Temp (Teff) | 6,203 K |
| Stellar Radius | 1.1940 R☉ |
| Stellar Mass | 1.1260 M☉ |
| Bolometric Luminosity | 1.894 L☉ |
| Metallicity [Fe/H] | -0.120 dex |
| Stellar Age | 3.000 Gyr |
| Apparent Magnitude | V: 7.940 · G: 7.804 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.120200 AU |
| Orbital Period | 14.339 days |
| Mean Orbital Velocity | 91.2 km/s |
| Orbital Eccentricity (e) | 0.08000 |
| Orbital Inclination (i) | 89.2700° |
| Mean Bulk Density | 2.92 g/cm³ (20 km/s vesc) |
| Insolation Flux | 132.0000 S⊕ (~179,652 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 187.800 LY (57.585 pc) |