K2-105 b
K2-105 b is a sub-Neptune orbiting K2-105 in the constellation Cancer. It lies about 646 light-years from Earth and was discovered in 2017 using the transit method.
How Big Is K2-105 b?
K2-105 b has a radius of 3.40 times that of Earth. Its mass is 15.4 times that of Earth, giving it a density of 2.24 g/cm³ — between that of rocky and gaseous planets.
Is K2-105 b in the Habitable Zone?
The position of K2-105 b relative to the habitable zone of K2-105 cannot be precisely determined from the available orbital data.
Habitable zone of K2-105: 0.601–1.434 AU (conservative: 0.762–1.359 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-105 b
The equilibrium temperature of K2-105 b is about 805 K (532 °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. It receives 100 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-105 b — one full orbit around K2-105 — lasts 8.27 Earth days, shorter than Mercury's 88-day year.
How Was K2-105 b Discovered?
K2-105 b was discovered in 2017 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 K2-105 b?
K2-105 b is 645.8 light-years (198.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1381. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 11,366,080 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. K2-105 b scores 0.20, ranking #3,871 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-105
K2-105
- Surface temperature
- 5,373 K (Sun: 5,772 K)
- Mass
- 0.94 M☉
- Radius
- 0.91 R☉
Planetary System
K2-105 b is the only planet known to orbit K2-105 so far.
K2-105 b — Complete Data
| Radius | 3.400 Earth radii (0.303 Jupiter radii) |
|---|---|
| Mass | 15.40 Earth masses (0.048 Jupiter masses) |
| Density | 2.24 g/cm³ (Earth: 5.51) |
| Orbital period | 8.27 days |
| Equilibrium temperature | 805 K (532 °C) |
| Stellar irradiation | 100.00× Earth |
| Earth Similarity Index | 0.20 |
| Distance from Earth | 645.8 light-years (198.0 parsecs) |
| Constellation | Cancer |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2025-09-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-105 b
Is K2-105 b habitable?
K2-105 b is not known to orbit within the habitable zone of K2-105, and as a sub-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-105 b?
K2-105 b is about 646 light-years from Earth in the constellation Cancer. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 11,366,080 years to get there.
How big is K2-105 b compared to Earth?
K2-105 b has 3.40 times the radius of Earth and about 15.4 times its mass.
How long is a year on K2-105 b?
One orbit around K2-105 takes 8.3 Earth days — short enough that 44 of its years would fit into one Earth year.
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