NN Ser d
Astrophysical Synthesis & Habitability Characterization
NN Ser d is a confirmed gas giant exoplanet orbiting the star NN Ser, located approximately 1682.4 light-years (515.82 parsecs) from the Solar System. First announced in 2010 by Multiple Observatories using the Eclipse Timing Variations detection technique, this world measures 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 724.622 Earth masses (2.28 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.7 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.1 g⊕ (40.21 m/s²), and an escape velocity of 82.6 km/s.
In its orbital architecture around NN Ser, NN Ser d completes one full revolution every 2880 Earth days (7.89Julian years) at a semi-major axis of 3.39 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 12.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.24 carries the world between 2.5764 AU at periapsis and 4.2036 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.300 R⊕, NN Ser d 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 NN Ser is classified as an evolved stellar remnant of spectral type WD with an effective photospheric temperature of 57,000 K, a mass of 0.535 M☉. From Earth, NN Ser shines at apparent V-band magnitude 16.943 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The NN Ser system is a multi-planet architecture hosting 2 confirmed worlds, with NN Ser d sharing its stellar neighborhood alongside NN Ser 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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | NN Ser |
| Spectral Type | WD |
| Effective Temp (Teff) | 57,000 K |
| Stellar Radius | — |
| Stellar Mass | 0.5350 M☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 16.943 · G: 16.591 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 3.390000 AU |
| Orbital Period | 2880 days |
| Mean Orbital Velocity | 12.8 km/s |
| Orbital Eccentricity (e) | 0.24000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.7 g/cm³ (82.6 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1682.400 LY (515.818 pc) |