K2-19 d
Astrophysical Synthesis & Habitability Characterization
K2-19 d is a confirmed terrestrial exoplanet orbiting the star K2-19, located approximately 945.3 light-years (289.83 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0135% across the stellar disk), this world measures 1.044 Earth radii and has a measured mass of 6.2 Earth masses. Combining its mass and radius yields a mean bulk density of 30.04 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 5.69 g⊕ (55.8 m/s²), and an escape velocity of 27.3 km/s.
In its orbital architecture around K2-19, K2-19 d completes one full revolution every 2.508 Earth days at a semi-major axis of 0.03478 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 150.9 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.44, swinging from 0.0195 AU at periapsis out to 0.0501 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1258 K (+985°C / +1805°F) and receiving 404.00 S⊕ (~549,844 W/m²), K2-19 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-19 is classified as a solar-type yellow star of spectral type G9 with an effective photospheric temperature of 5,350 K, a radius of 0.824 R☉, a mass of 0.892 M☉, an estimated bolometric luminosity of 0.499 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.7 Gyr and a metallicity of [Fe/H] = 0.03 dex (near-solar heavy-element abundance). From Earth, K2-19 shines at apparent V-band magnitude 13.024 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-19 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-19 d sharing its stellar neighborhood alongside K2-19 b, K2-19 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 | K2-19 |
| Spectral Type | G9 |
| Effective Temp (Teff) | 5,350 K |
| Stellar Radius | 0.8240 R☉ |
| Stellar Mass | 0.8920 M☉ |
| Bolometric Luminosity | 0.499 L☉ |
| Metallicity [Fe/H] | 0.030 dex |
| Stellar Age | 1.700 Gyr |
| Apparent Magnitude | V: 13.024 · G: 12.815 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.034780 AU |
| Orbital Period | 2.508 days |
| Mean Orbital Velocity | 150.9 km/s |
| Orbital Eccentricity (e) | 0.44000 |
| Orbital Inclination (i) | 89.7000° |
| Mean Bulk Density | 30.04 g/cm³ (27.3 km/s vesc) |
| Insolation Flux | 404.0000 S⊕ (~549,844 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 945.300 LY (289.827 pc) |