HD 219666 b
HD 219666 b is a Neptune-like planet orbiting HD 219666 in the constellation Tucana. It lies about 307 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is HD 219666 b?
HD 219666 b has a radius of 4.90 times that of Earth. Its mass is 17.6 times that of Earth.
Is HD 219666 b in the Habitable Zone?
The position of HD 219666 b relative to the habitable zone of HD 219666 cannot be precisely determined from the available orbital data.
Habitable zone of HD 219666: 0.741–1.758 AU (conservative: 0.939–1.666 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 ›
Temperature on HD 219666 b
The equilibrium temperature of HD 219666 b is about 1,076 K (803 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on HD 219666 b — one full orbit around HD 219666 — lasts 6.03 Earth days, shorter than Mercury's 88-day year. Its orbit is mildly elliptical (eccentricity 0.05).
How Was HD 219666 b Discovered?
HD 219666 b was discovered in 2018 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is HD 219666 b?
HD 219666 b is 307.1 light-years (94.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1719. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 5,404,960 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 219666 b scores 0.18, ranking #4,028 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 219666
HD 219666
- Surface temperature
- 5,540 K (Sun: 5,772 K)
- Mass
- 1.02 M☉
- Radius
- 1.06 R☉
Planetary System
HD 219666 b is the only planet known to orbit HD 219666 so far.
HD 219666 b — Complete Data
| Radius | 4.898 Earth radii (0.437 Jupiter radii) |
|---|---|
| Mass | 17.60 Earth masses (0.055 Jupiter masses) |
| Orbital period | 6.03 days |
| Eccentricity | 0.050 |
| Equilibrium temperature | 1,076 K (803 °C) |
| Earth Similarity Index | 0.18 |
| Distance from Earth | 307.1 light-years (94.2 parsecs) |
| Constellation | Tucana |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2025-06-04. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 219666 b
Is HD 219666 b habitable?
HD 219666 b is not known to orbit within the habitable zone of HD 219666, and as a Neptune-like planet it is an unlikely candidate for life as we know it.
How far away is HD 219666 b?
HD 219666 b is about 307 light-years from Earth in the constellation Tucana. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 5,404,960 years to get there.
How big is HD 219666 b compared to Earth?
HD 219666 b has 4.90 times the radius of Earth and about 17.6 times its mass.
How long is a year on HD 219666 b?
One orbit around HD 219666 takes 6.0 Earth days — short enough that 61 of its years would fit into one Earth year.
Explore HD 219666 b in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
