Kepler-1661 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1661 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1661, located approximately 1339.2 light-years (410.61 parsecs) from the Solar System. First announced in 2020 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.2168% across the stellar disk), this world measures 3.87 Earth radii (0.35 Jupiter radii) and has a measured mass of 17 Earth masses. Combining its mass and radius yields a mean bulk density of 1.62 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.14 g⊕ (11.18 m/s²), and an escape velocity of 23.4 km/s.
In its orbital architecture around Kepler-1661, Kepler-1661 b completes one full revolution every 175.06 Earth days at a semi-major axis of 0.633 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 39.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.057 carries the world between 0.5969 AU at periapsis and 0.6691 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 3.870 R⊕, Kepler-1661 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star Kepler-1661 is classified as an orange K-type star of spectral type K with an effective photospheric temperature of 5,100 K, a radius of 0.762 R☉, a mass of 0.841 M☉, an estimated bolometric luminosity of 0.352 L☉. Stellar evolution modeling indicates an estimated stellar age of 2 Gyr and a metallicity of [Fe/H] = -0.12 dex (metal-poor relative to the Sun). From Earth, Kepler-1661 shines at apparent V-band magnitude 14.357 (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-1661 |
| Spectral Type | K |
| Effective Temp (Teff) | 5,100 K |
| Stellar Radius | 0.7620 R☉ |
| Stellar Mass | 0.8410 M☉ |
| Bolometric Luminosity | 0.352 L☉ |
| Metallicity [Fe/H] | -0.120 dex |
| Stellar Age | 2.000 Gyr |
| Apparent Magnitude | V: 14.357 · G: 14.193 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.633000 AU |
| Orbital Period | 175.06 days |
| Mean Orbital Velocity | 39.3 km/s |
| Orbital Eccentricity (e) | 0.05700 |
| Orbital Inclination (i) | 89.4600° |
| Mean Bulk Density | 1.62 g/cm³ (23.4 km/s vesc) |
| Insolation Flux | 0.8800 S⊕ (~1,198 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1339.200 LY (410.607 pc) |