K2-389 b
K2-389 b is a mini-Neptune orbiting K2-389 in the constellation Aquarius. It lies about 845 light-years from Earth and was discovered in 2022 using the transit method.
How Big Is K2-389 b?
K2-389 b has a radius of 2.33 times that of Earth.
Is K2-389 b in the Habitable Zone?
The position of K2-389 b relative to the habitable zone of K2-389 cannot be precisely determined from the available orbital data.
Habitable zone of K2-389: 0.820–1.932 AU (conservative: 1.038–1.831 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 ›
Temperature on K2-389 b
The equilibrium temperature of K2-389 b is about 932 K (659 °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 179 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-389 b — one full orbit around K2-389 — lasts 8.58 Earth days, shorter than Mercury's 88-day year.
How Was K2-389 b Discovered?
K2-389 b was discovered in 2022 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 K2-389 b?
K2-389 b is 845.4 light-years (259.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1181. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 14,879,040 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. K2-389 b scores 0.25, ranking #3,064 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-389
K2-389
- Surface temperature
- 5,773 K (Sun: 5,772 K)
- Mass
- 0.99 M☉
- Radius
- 1.09 R☉
The K2-389 Planetary System
K2-389 b is one of 2 known planets in the K2-389 system. Its siblings:
- K2-389 c (Mini Neptune)
K2-389 b — Complete Data
| Radius | 2.330 Earth radii (0.208 Jupiter radii) |
|---|---|
| Orbital period | 8.58 days |
| Equilibrium temperature | 932 K (659 °C) |
| Stellar irradiation | 179.00× Earth |
| Earth Similarity Index | 0.25 |
| Distance from Earth | 845.4 light-years (259.2 parsecs) |
| Constellation | Aquarius |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2022 |
Data: NASA Exoplanet Archive, last updated 2025-09-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-389 b
Is K2-389 b habitable?
K2-389 b is not known to orbit within the habitable zone of K2-389, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-389 b?
K2-389 b is about 845 light-years from Earth in the constellation Aquarius. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 14,879,040 years to get there.
How big is K2-389 b compared to Earth?
K2-389 b has 2.33 times the radius of Earth.
How long is a year on K2-389 b?
One orbit around K2-389 takes 8.6 Earth days — short enough that 43 of its years would fit into one Earth year.
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