HAT-P-28 b
Astrophysical Synthesis & Habitability Characterization
HAT-P-28 b is a confirmed gas giant exoplanet orbiting the star HAT-P-28, located approximately 1308.9 light-years (401.32 parsecs) from the Solar System. First announced in 2011 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 1.275% across the stellar disk), this world measures 13.585 Earth radii (1.21 Jupiter radii) and has a measured mass of 198.953 Earth masses (0.63 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.44 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 42.8 km/s.
In its orbital architecture around HAT-P-28, HAT-P-28 b completes one full revolution every 3.257 Earth days at a semi-major axis of 0.0434 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 145 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.051 carries the world between 0.0412 AU at periapsis and 0.0456 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1384 K (+1111°C / +2032°F) and receiving 554.71 S⊕ (~754,963 W/m²), HAT-P-28 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HAT-P-28 is classified as a solar-type yellow star of spectral type G3 with an effective photospheric temperature of 5,680 K, a radius of 1.103 R☉, a mass of 1.025 M☉, an estimated bolometric luminosity of 1.136 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.1 Gyr and a metallicity of [Fe/H] = 0.12 dex (metal-rich relative to the Sun). From Earth, HAT-P-28 shines at apparent V-band magnitude 13.098 (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: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HAT-P-28 |
| Spectral Type | G3 |
| Effective Temp (Teff) | 5,680 K |
| Stellar Radius | 1.1030 R☉ |
| Stellar Mass | 1.0250 M☉ |
| Bolometric Luminosity | 1.136 L☉ |
| Metallicity [Fe/H] | 0.120 dex |
| Stellar Age | 6.100 Gyr |
| Apparent Magnitude | V: 13.098 · G: 12.872 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.043400 AU |
| Orbital Period | 3.257 days |
| Mean Orbital Velocity | 145 km/s |
| Orbital Eccentricity (e) | 0.05100 |
| Orbital Inclination (i) | 88.0000° |
| Mean Bulk Density | 0.44 g/cm³ (42.8 km/s vesc) |
| Insolation Flux | 554.7122 S⊕ (~754,963 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1308.900 LY (401.319 pc) |