K2-25 b
K2-25 b is a super-Earth orbiting the M4.5 V star K2-25 in the constellation Taurus. It lies about 147 light-years from Earth and was discovered in 2015 using the transit method.
How Big Is K2-25 b?
K2-25 b has a radius of 3.44 times that of Earth. Its mass is 24.5 times that of Earth.
Is K2-25 b in the Habitable Zone?
K2-25 b orbits inside the inner edge of the habitable zone of K2-25. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-25: 0.074–0.195 AU (conservative: 0.094–0.185 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-25 b
The equilibrium temperature of K2-25 b is about 494 K (221 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 9.91 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-25 b — one full orbit around K2-25 — lasts 3.48 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.029 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.43), swinging dramatically closer to and farther from its star.
How Was K2-25 b Discovered?
K2-25 b was discovered in 2015 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 K2-25 b?
K2-25 b is 146.6 light-years (45.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1880. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,580,160 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. K2-25 b scores 0.29, ranking #1,592 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-25
K2-25
- Spectral type
- M4.5 V
- Surface temperature
- 3,207 K (Sun: 5,772 K)
- Mass
- 0.26 M☉
- Radius
- 0.29 R☉
- Luminosity
- 0.0082 L☉
- Age
- 0.7 billion years (Sun: 4.6)
Planetary System
K2-25 b is the only planet known to orbit K2-25 so far.
K2-25 b — Complete Data
| Radius | 3.440 Earth radii (0.306 Jupiter radii) |
|---|---|
| Mass | 24.50 Earth masses (0.077 Jupiter masses) |
| Orbital period | 3.48 days |
| Orbital distance | 0.029 AU |
| Eccentricity | 0.428 |
| Equilibrium temperature | 494 K (221 °C) |
| Stellar irradiation | 9.91× Earth |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 146.6 light-years (45.0 parsecs) |
| Constellation | Taurus |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2015 |
Data: NASA Exoplanet Archive, last updated 2022-03-28. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-25 b
Is K2-25 b habitable?
No — K2-25 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-25 b?
K2-25 b is about 147 light-years from Earth in the constellation Taurus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,580,160 years to get there.
How big is K2-25 b compared to Earth?
K2-25 b has 3.44 times the radius of Earth and about 24.5 times its mass.
How long is a year on K2-25 b?
One orbit around K2-25 takes 3.5 Earth days — short enough that 105 of its years would fit into one Earth year.
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