K2-398 b
K2-398 b is a mini-Neptune orbiting K2-398 in the constellation Sextans. It lies about 1,980 light-years from Earth and was discovered in 2022 using the transit method.
How Big Is K2-398 b?
K2-398 b has a radius of 2.27 times that of Earth.
Is K2-398 b in the Habitable Zone?
The position of K2-398 b relative to the habitable zone of K2-398 cannot be precisely determined from the available orbital data.
Habitable zone of K2-398: 0.975–2.287 AU (conservative: 1.235–2.168 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 K2-398 b — one full orbit around K2-398 — lasts 6.39 Earth days, shorter than Mercury's 88-day year.
How Was K2-398 b Discovered?
K2-398 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 K2-398 b?
K2-398 b is 1,979.7 light-years (607.0 parsecs) from Earth. Light arriving here tonight left the planet about 1,980 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 34,842,720 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. K2-398 b scores 0.24, ranking #3,224 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-398
K2-398
- Surface temperature
- 5,946 K (Sun: 5,772 K)
- Mass
- 0.95 M☉
- Radius
- 1.24 R☉
The K2-398 Planetary System
K2-398 b is one of 2 known planets in the K2-398 system. Its siblings:
- K2-398 c (Neptune-like)
K2-398 b — Complete Data
| Radius | 2.274 Earth radii (0.203 Jupiter radii) |
|---|---|
| Orbital period | 6.39 days |
| Earth Similarity Index | 0.24 |
| Distance from Earth | 1,979.7 light-years (607.0 parsecs) |
| Constellation | Sextans |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2022 |
Data: NASA Exoplanet Archive, last updated 2022-03-16. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-398 b
Is K2-398 b habitable?
K2-398 b is not known to orbit within the habitable zone of K2-398, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-398 b?
K2-398 b is about 1,980 light-years from Earth in the constellation Sextans. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 34,842,720 years to get there.
How big is K2-398 b compared to Earth?
K2-398 b has 2.27 times the radius of Earth.
How long is a year on K2-398 b?
One orbit around K2-398 takes 6.4 Earth days — short enough that 57 of its years would fit into one Earth year.
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