HD 216520 b
HD 216520 b is a Neptune-like planet orbiting HD 216520 in the constellation Cepheus. It lies about 64 light-years from Earth and was discovered in 2020 using the radial velocity method.
Is HD 216520 b in the Habitable Zone?
HD 216520 b orbits inside the inner edge of the habitable zone of HD 216520. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 216520: 0.463–1.115 AU (conservative: 0.587–1.057 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on HD 216520 b — one full orbit around HD 216520 — lasts 35.5 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.198 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.09).
How Was HD 216520 b Discovered?
HD 216520 b was discovered in 2020 using the radial velocity method, with observations from Multiple Observatories.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is HD 216520 b?
HD 216520 b is 63.8 light-years (19.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1963. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,122,880 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. HD 216520 b scores 0.32, ranking #977 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 216520
HD 216520
- Surface temperature
- 5,103 K (Sun: 5,772 K)
- Mass
- 0.82 M☉
- Radius
- 0.76 R☉
- Luminosity
- 0.3532 L☉
- Age
- 6.0 billion years (Sun: 4.6)
The HD 216520 Planetary System
HD 216520 b is one of 2 known planets in the HD 216520 system. Its siblings:
- HD 216520 c (Super Earth)
HD 216520 b — Complete Data
| Mass (best estimate) | 10.26 Earth masses |
|---|---|
| Orbital period | 35.45 days |
| Orbital distance | 0.198 AU |
| Eccentricity | 0.090 |
| Earth Similarity Index | 0.32 |
| Distance from Earth | 63.8 light-years (19.6 parsecs) |
| Constellation | Cepheus |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2020 |
Data: NASA Exoplanet Archive, last updated 2020-12-10. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 216520 b
Is HD 216520 b habitable?
No — HD 216520 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 216520 b?
HD 216520 b is about 64 light-years from Earth in the constellation Cepheus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,122,880 years to get there.
How long is a year on HD 216520 b?
One orbit around HD 216520 takes 35.5 Earth days — short enough that 10 of its years would fit into one Earth year.
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