Kepler-166 d
Kepler-166 d is a super-Earth orbiting Kepler-166 in the constellation Cygnus. It lies about 1,968 light-years from Earth and was discovered in 2016 using the transit method.
How Big Is Kepler-166 d?
Kepler-166 d has a radius of 1.73 times that of Earth.
Is Kepler-166 d in the Habitable Zone?
The position of Kepler-166 d relative to the habitable zone of Kepler-166 cannot be precisely determined from the available orbital data.
Habitable zone of Kepler-166: 0.547–1.307 AU (conservative: 0.693–1.239 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 Kepler-166 d — one full orbit around Kepler-166 — lasts just 37.3 hours, shorter than Mercury's 88-day year.
How Was Kepler-166 d Discovered?
Kepler-166 d was discovered in 2016 using the transit method, with observations from Kepler.
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 Kepler-166 d?
Kepler-166 d is 1,968.4 light-years (603.5 parsecs) from Earth. Light arriving here tonight left the planet about 1,968 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 34,643,840 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. Kepler-166 d scores 0.27, ranking #2,615 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-166
Kepler-166
- Surface temperature
- 5,350 K (Sun: 5,772 K)
- Mass
- 0.88 M☉
- Radius
- 0.83 R☉
- Age
- 4.5 billion years (Sun: 4.6)
The Kepler-166 Planetary System
Kepler-166 d is one of 3 known planets in the Kepler-166 system. Its siblings:
- Kepler-166 b (Mini Neptune)
- Kepler-166 c (Mini Neptune)
Kepler-166 d — Complete Data
| Radius | 1.730 Earth radii (0.154 Jupiter radii) |
|---|---|
| Orbital period | 1.55 days |
| Earth Similarity Index | 0.27 |
| Distance from Earth | 1,968.4 light-years (603.5 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2016-05-06. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-166 d
Is Kepler-166 d habitable?
Kepler-166 d is not known to orbit within the habitable zone of Kepler-166, and as a super-Earth it is an unlikely candidate for life as we know it.
How far away is Kepler-166 d?
Kepler-166 d is about 1,968 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 34,643,840 years to get there.
How big is Kepler-166 d compared to Earth?
Kepler-166 d has 1.73 times the radius of Earth.
How long is a year on Kepler-166 d?
One orbit around Kepler-166 takes 1.6 Earth days — short enough that 235 of its years would fit into one Earth year.
Explore Kepler-166 d in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
