GJ 9827 d
Astrophysical Synthesis & Habitability Characterization
GJ 9827 d is a confirmed super-earth exoplanet orbiting the star GJ 9827, located approximately 96.7 light-years (29.66 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.098% across the stellar disk), this world measures 1.98 Earth radii and has a measured mass of 3.02 Earth masses. Combining its mass and radius yields a mean bulk density of 2.15 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 0.77 g⊕ (7.55 m/s²), and an escape velocity of 13.8 km/s.
In its orbital architecture around GJ 9827, GJ 9827 d completes one full revolution every 6.202 Earth days at a semi-major axis of 0.053 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 93 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 675 K (+402°C / +756°F) and receiving 34.90 S⊕ (~47,499 W/m²), GJ 9827 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 9827 is classified as an orange K-type star of spectral type K7 V with an effective photospheric temperature of 4,236 K, a radius of 0.58 R☉, a mass of 0.62 M☉, an estimated bolometric luminosity of 0.097 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.465 Gyr and a metallicity of [Fe/H] = -0.29 dex (metal-poor relative to the Sun). From Earth, GJ 9827 shines at apparent V-band magnitude 10.37 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The GJ 9827 system is a multi-planet architecture hosting 3 confirmed worlds, with GJ 9827 d sharing its stellar neighborhood alongside GJ 9827 b, GJ 9827 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 9827 |
| Spectral Type | K7 V |
| Effective Temp (Teff) | 4,236 K |
| Stellar Radius | 0.5800 R☉ |
| Stellar Mass | 0.6200 M☉ |
| Bolometric Luminosity | 0.097 L☉ |
| Metallicity [Fe/H] | -0.290 dex |
| Stellar Age | 5.465 Gyr |
| Apparent Magnitude | V: 10.370 · G: 9.838 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.053000 AU |
| Orbital Period | 6.202 days |
| Mean Orbital Velocity | 93 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.4100° |
| Mean Bulk Density | 2.15 g/cm³ (13.8 km/s vesc) |
| Insolation Flux | 34.9000 S⊕ (~47,499 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 96.700 LY (29.661 pc) |