K2-166 b
K2-166 b is a mini-Neptune orbiting K2-166 in the constellation Virgo. It lies about 1,555 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-166 b?
K2-166 b has a radius of 2.19 times that of Earth.
Is K2-166 b in the Habitable Zone?
K2-166 b orbits inside the inner edge of the habitable zone of K2-166. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-166: 1.271–2.982 AU (conservative: 1.610–2.827 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 K2-166 b
The equilibrium temperature of K2-166 b is about 1,140 K (867 °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 K2-166 b — one full orbit around K2-166 — lasts 8.53 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.086 AU — closer to its star than Mercury is to the Sun.
How Was K2-166 b Discovered?
K2-166 b was discovered in 2018 using the transit method, with observations from K2.
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 K2-166 b?
K2-166 b is 1,555.4 light-years (476.9 parsecs) from Earth. Light arriving here tonight left the planet about 1,555 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 27,375,040 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. K2-166 b scores 0.25, ranking #3,132 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-166
K2-166
- Surface temperature
- 5,960 K (Sun: 5,772 K)
- Mass
- 1.16 M☉
- Radius
- 1.61 R☉
The K2-166 Planetary System
K2-166 b is one of 2 known planets in the K2-166 system. Its siblings:
- EPIC 201615463 c (Terrestrial)
K2-166 b — Complete Data
| Radius | 2.190 Earth radii (0.195 Jupiter radii) |
|---|---|
| Orbital period | 8.53 days |
| Orbital distance | 0.086 AU |
| Equilibrium temperature | 1,140 K (867 °C) |
| Earth Similarity Index | 0.25 |
| Distance from Earth | 1,555.4 light-years (476.9 parsecs) |
| Constellation | Virgo |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2022-03-28. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-166 b
Is K2-166 b habitable?
No — K2-166 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-166 b?
K2-166 b is about 1,555 light-years from Earth in the constellation Virgo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 27,375,040 years to get there.
How big is K2-166 b compared to Earth?
K2-166 b has 2.19 times the radius of Earth.
How long is a year on K2-166 b?
One orbit around K2-166 takes 8.5 Earth days — short enough that 43 of its years would fit into one Earth year.
Explore K2-166 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.
