HIP 9618 c
Astrophysical Synthesis & Habitability Characterization
HIP 9618 c is a confirmed sub-neptune exoplanet orbiting the star HIP 9618, located approximately 220.3 light-years (67.55 parsecs) from the Solar System. First announced in 2023 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.1074% across the stellar disk), this world measures 3.429 Earth radii (0.31 Jupiter radii) and has a measured mass of 7 Earth masses. Combining its mass and radius yields a mean bulk density of 0.96 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.6 g⊕ (5.88 m/s²), and an escape velocity of 16 km/s.
In its orbital architecture around HIP 9618, HIP 9618 c completes one full revolution every 52.564 Earth days at a semi-major axis of 0.269 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 55.7 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 470 K (+197°C / +387°F) and receiving 11.70 S⊕ (~15,924 W/m²), HIP 9618 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HIP 9618 is classified as a stellar host with an effective photospheric temperature of 5,649 K, a radius of 0.9593 R☉, a mass of 0.942 M☉, an estimated bolometric luminosity of 0.841 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.6 Gyr and a metallicity of [Fe/H] = -0.018 dex (near-solar heavy-element abundance). From Earth, HIP 9618 shines at apparent V-band magnitude 9.2 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HIP 9618 system is a multi-planet architecture hosting 2 confirmed worlds, with HIP 9618 c sharing its stellar neighborhood alongside HIP 9618 b.
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 | HIP 9618 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,649 K |
| Stellar Radius | 0.9593 R☉ |
| Stellar Mass | 0.9420 M☉ |
| Bolometric Luminosity | 0.841 L☉ |
| Metallicity [Fe/H] | -0.018 dex |
| Stellar Age | 5.600 Gyr |
| Apparent Magnitude | V: 9.200 · G: 9.025 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.269000 AU |
| Orbital Period | 52.564 days |
| Mean Orbital Velocity | 55.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.96 g/cm³ (16 km/s vesc) |
| Insolation Flux | 11.7000 S⊕ (~15,924 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 220.300 LY (67.548 pc) |