K2-218 b
K2-218 b is a mini-Neptune orbiting K2-218 in the constellation Pisces. It lies about 1,285 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-218 b?
K2-218 b has a radius of 2.57 times that of Earth.
Is K2-218 b in the Habitable Zone?
The position of K2-218 b relative to the habitable zone of K2-218 cannot be precisely determined from the available orbital data.
Habitable zone of K2-218: 0.752–1.773 AU (conservative: 0.953–1.681 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 K2-218 b — one full orbit around K2-218 — lasts 8.68 Earth days, shorter than Mercury's 88-day year.
How Was K2-218 b Discovered?
K2-218 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 K2-218 b?
K2-218 b is 1,285.3 light-years (394.1 parsecs) from Earth. Light arriving here tonight left the planet about 1,285 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 22,621,280 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. K2-218 b scores 0.24, ranking #3,386 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-218
K2-218
- Surface temperature
- 5,757 K (Sun: 5,772 K)
- Mass
- 1.05 M☉
- Radius
- 1.01 R☉
Planetary System
K2-218 b is the only planet known to orbit K2-218 so far.
K2-218 b — Complete Data
| Radius | 2.569 Earth radii (0.229 Jupiter radii) |
|---|---|
| Orbital period | 8.68 days |
| Earth Similarity Index | 0.24 |
| Distance from Earth | 1,285.3 light-years (394.1 parsecs) |
| Constellation | Pisces |
| 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 K2-218 b
Is K2-218 b habitable?
K2-218 b is not known to orbit within the habitable zone of K2-218, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-218 b?
K2-218 b is about 1,285 light-years from Earth in the constellation Pisces. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 22,621,280 years to get there.
How big is K2-218 b compared to Earth?
K2-218 b has 2.57 times the radius of Earth.
How long is a year on K2-218 b?
One orbit around K2-218 takes 8.7 Earth days — short enough that 42 of its years would fit into one Earth year.
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