Kepler-1878 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1878 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1878, located approximately 4873.7 light-years (1494.3 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0958% across the stellar disk), this world measures 2.92 Earth radii and has a measured mass of 8.86 Earth masses. Combining its mass and radius yields a mean bulk density of 1.96 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.5 km/s.
In its orbital architecture around Kepler-1878, Kepler-1878 b completes one full revolution every 4.446 Earth days at a semi-major axis of 0.0521 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 127.5 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 1063 K (+790°C / +1454°F) and receiving 302.60 S⊕ (~411,839 W/m²), Kepler-1878 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1878 is classified as a stellar host with an effective photospheric temperature of 5,918 K, a radius of 0.865 R☉, a mass of 0.956 M☉, an estimated bolometric luminosity of 0.823 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.26 dex (metal-poor relative to the Sun). From Earth, Kepler-1878 shines at apparent V-band magnitude 15.587 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-1878 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,918 K |
| Stellar Radius | 0.8650 R☉ |
| Stellar Mass | 0.9560 M☉ |
| Bolometric Luminosity | 0.823 L☉ |
| Metallicity [Fe/H] | -0.260 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 15.587 · G: 15.403 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.052100 AU |
| Orbital Period | 4.446 days |
| Mean Orbital Velocity | 127.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 86.1800° |
| Mean Bulk Density | 1.96 g/cm³ (19.5 km/s vesc) |
| Insolation Flux | 302.6000 S⊕ (~411,839 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4873.700 LY (1494.300 pc) |