K2-84 c
Astrophysical Synthesis & Habitability Characterization
K2-84 c is a confirmed sub-neptune exoplanet orbiting the star K2-84, located approximately 929.1 light-years (284.88 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.04% across the stellar disk), this world measures 2.03 Earth radii and has a measured mass of 4.78 Earth masses. Combining its mass and radius yields a mean bulk density of 3.15 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.16 g⊕ (11.38 m/s²), and an escape velocity of 17.2 km/s.
In its orbital architecture around K2-84, K2-84 c completes one full revolution every 27.86 Earth days at a semi-major axis of 0.1768 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 69 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 625 K (+352°C / +666°F) and receiving 25.30 S⊕ (~34,433 W/m²), K2-84 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-84 is classified as a stellar host with an effective photospheric temperature of 5,652 K, a radius of 0.93 R☉, a mass of 0.95 M☉, an estimated bolometric luminosity of 0.792 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.278 dex (metal-rich relative to the Sun). From Earth, K2-84 shines at apparent V-band magnitude 13.386 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-84 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-84 c sharing its stellar neighborhood alongside K2-84 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-84 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,652 K |
| Stellar Radius | 0.9300 R☉ |
| Stellar Mass | 0.9500 M☉ |
| Bolometric Luminosity | 0.792 L☉ |
| Metallicity [Fe/H] | 0.278 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.386 · G: 13.147 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.176800 AU |
| Orbital Period | 27.86 days |
| Mean Orbital Velocity | 69 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 3.15 g/cm³ (17.2 km/s vesc) |
| Insolation Flux | 25.3000 S⊕ (~34,433 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 929.100 LY (284.876 pc) |