HD 278555 b
Astrophysical Synthesis & Habitability Characterization
HD 278555 b is a confirmed gas giant exoplanet orbiting the star HD 278555, located approximately 945.3 light-years (289.83 parsecs) from the Solar System. First announced in 2026 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.3877% across the stellar disk), this world measures 11.03 Earth radii (0.98 Jupiter radii) and has a measured mass of 266.976 Earth masses (0.84 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.1 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.19 g⊕ (21.48 m/s²), and an escape velocity of 55 km/s.
In its orbital architecture around HD 278555, HD 278555 b completes one full revolution every 28.842 Earth days at a semi-major axis of 0.1985 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 74.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.085 carries the world between 0.1816 AU at periapsis and 0.2154 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 853 K (+580°C / +1076°F) and receiving 79.44 S⊕ (~108,114 W/m²), HD 278555 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 278555 is classified as a warm F-type star of spectral type F8 with an effective photospheric temperature of 6,047 K, a radius of 1.624 R☉, a mass of 1.255 M☉, an estimated bolometric luminosity of 3.164 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.8 Gyr and a metallicity of [Fe/H] = 0.269 dex (metal-rich relative to the Sun). From Earth, HD 278555 shines at apparent V-band magnitude 11.046 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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 278555 |
| Spectral Type | F8 |
| Effective Temp (Teff) | 6,047 K |
| Stellar Radius | 1.6240 R☉ |
| Stellar Mass | 1.2550 M☉ |
| Bolometric Luminosity | 3.164 L☉ |
| Metallicity [Fe/H] | 0.269 dex |
| Stellar Age | 3.800 Gyr |
| Apparent Magnitude | V: 11.046 · G: 10.892 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.198500 AU |
| Orbital Period | 28.842 days |
| Mean Orbital Velocity | 74.9 km/s |
| Orbital Eccentricity (e) | 0.08500 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.1 g/cm³ (55 km/s vesc) |
| Insolation Flux | 79.4371 S⊕ (~108,114 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 945.300 LY (289.829 pc) |