Kepler-296 d
Astrophysical Synthesis & Habitability Characterization
Kepler-296 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-296, located approximately 544.7 light-years (167 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1593% across the stellar disk), this world measures 2.09 Earth radii and has a measured mass of 5.02 Earth masses. Combining its mass and radius yields a mean bulk density of 3.03 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.15 g⊕ (11.28 m/s²), and an escape velocity of 17.3 km/s.
In its orbital architecture around Kepler-296, Kepler-296 d completes one full revolution every 19.85 Earth days at a semi-major axis of 0.118 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 64.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.33, swinging from 0.0791 AU at periapsis out to 0.1569 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 403 K (+130°C / +266°F) and receiving 2.90 S⊕ (~3,947 W/m²), Kepler-296 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-296 is classified as a low-mass red dwarf of spectral type M2 V with an effective photospheric temperature of 3,740 K, a radius of 0.48 R☉, a mass of 0.498 M☉, an estimated bolometric luminosity of 0.04 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.2 Gyr and a metallicity of [Fe/H] = -0.08 dex (near-solar heavy-element abundance). From Earth, Kepler-296 shines at apparent V-band magnitude 16.363 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-296 system is a multi-planet architecture hosting 5 confirmed worlds, with Kepler-296 d sharing its stellar neighborhood alongside Kepler-296 c, Kepler-296 b, Kepler-296 e, Kepler-296 f.
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-296 |
| Spectral Type | M2 V |
| Effective Temp (Teff) | 3,740 K |
| Stellar Radius | 0.4800 R☉ |
| Stellar Mass | 0.4980 M☉ |
| Bolometric Luminosity | 0.04 L☉ |
| Metallicity [Fe/H] | -0.080 dex |
| Stellar Age | 4.200 Gyr |
| Apparent Magnitude | V: 16.363 · G: 15.902 |
| System Architecture | 2 Stars, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.118000 AU |
| Orbital Period | 19.85 days |
| Mean Orbital Velocity | 64.7 km/s |
| Orbital Eccentricity (e) | 0.33000 |
| Orbital Inclination (i) | 89.7700° |
| Mean Bulk Density | 3.03 g/cm³ (17.3 km/s vesc) |
| Insolation Flux | 2.9000 S⊕ (~3,947 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 544.700 LY (167.000 pc) |