K2-171 b
K2-171 b is a mini-Neptune orbiting K2-171 in the constellation Aquarius. It lies about 1,977 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-171 b?
K2-171 b has a radius of 2.69 times that of Earth.
Is K2-171 b in the Habitable Zone?
The position of K2-171 b relative to the habitable zone of K2-171 cannot be precisely determined from the available orbital data.
Habitable zone of K2-171: 1.097–2.627 AU (conservative: 1.389–2.490 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 K2-171 b — one full orbit around K2-171 — lasts 5.63 Earth days, shorter than Mercury's 88-day year.
How Was K2-171 b Discovered?
K2-171 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 K2-171 b?
K2-171 b is 1,976.9 light-years (606.1 parsecs) from Earth. Light arriving here tonight left the planet about 1,977 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 34,793,440 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. K2-171 b scores 0.22, ranking #3,598 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-171
K2-171
- Surface temperature
- 5,250 K (Sun: 5,772 K)
- Mass
- 0.89 M☉
- Radius
- 1.72 R☉
Planetary System
K2-171 b is the only planet known to orbit K2-171 so far.
K2-171 b — Complete Data
| Radius | 2.687 Earth radii (0.240 Jupiter radii) |
|---|---|
| Orbital period | 5.63 days |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 1,976.9 light-years (606.1 parsecs) |
| Constellation | Aquarius |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2018-02-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-171 b
Is K2-171 b habitable?
K2-171 b is not known to orbit within the habitable zone of K2-171, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-171 b?
K2-171 b is about 1,977 light-years from Earth in the constellation Aquarius. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 34,793,440 years to get there.
How big is K2-171 b compared to Earth?
K2-171 b has 2.69 times the radius of Earth.
How long is a year on K2-171 b?
One orbit around K2-171 takes 5.6 Earth days — short enough that 65 of its years would fit into one Earth year.
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