HD 153557 b
Astrophysical Synthesis & Habitability Characterization
HD 153557 b is a confirmed sub-neptune exoplanet orbiting the star HD 153557, located approximately 58.5 light-years (17.94 parsecs) from the Solar System. First announced in 2022 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.77 Earth radii (0.43 Jupiter radii) and has a measured mass of 20.341 Earth masses. Combining its mass and radius yields a mean bulk density of 1.03 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.89 g⊕ (8.73 m/s²), and an escape velocity of 23.1 km/s.
In its orbital architecture around HD 153557, HD 153557 b completes one full revolution every 7.299 Earth days at a semi-major axis of 0.068 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 101.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.065 carries the world between 0.0636 AU at periapsis and 0.0724 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 772 K (+499°C / +930°F) and receiving 59.22 S⊕ (~80,603 W/m²), HD 153557 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 153557 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 4,837 K, a radius of 0.7452 R☉, a mass of 0.79 M☉, an estimated bolometric luminosity of 0.273 L☉. From Earth, HD 153557 shines at apparent V-band magnitude 7.83 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 153557 system is a multi-planet architecture hosting 3 confirmed worlds, with HD 153557 b sharing its stellar neighborhood alongside HD 153557 c, HD 153557 d.
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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 153557 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 4,837 K |
| Stellar Radius | 0.7452 R☉ |
| Stellar Mass | 0.7900 M☉ |
| Bolometric Luminosity | 0.273 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 7.830 · G: 7.505 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.068000 AU |
| Orbital Period | 7.299 days |
| Mean Orbital Velocity | 101.4 km/s |
| Orbital Eccentricity (e) | 0.06500 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.03 g/cm³ (23.1 km/s vesc) |
| Insolation Flux | 59.2234 S⊕ (~80,603 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 58.500 LY (17.941 pc) |