K2-172 c
K2-172 c is a sub-Neptune orbiting K2-172 in the constellation Aquarius. It lies about 815 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-172 c?
K2-172 c has a radius of 3.21 times that of Earth.
Is K2-172 c in the Habitable Zone?
The position of K2-172 c relative to the habitable zone of K2-172 cannot be precisely determined from the available orbital data.
Habitable zone of K2-172: 0.613–1.453 AU (conservative: 0.777–1.378 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 K2-172 c — one full orbit around K2-172 — lasts 29.6 Earth days, shorter than Mercury's 88-day year.
How Was K2-172 c Discovered?
K2-172 c 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 K2-172 c?
K2-172 c is 814.5 light-years (249.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1212. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 14,335,200 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. K2-172 c scores 0.26, ranking #2,759 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-172
K2-172
- Surface temperature
- 5,569 K (Sun: 5,772 K)
- Mass
- 0.93 M☉
- Radius
- 0.87 R☉
The K2-172 Planetary System
K2-172 c is one of 2 known planets in the K2-172 system. Its siblings:
- K2-172 b (Super Earth)
K2-172 c — Complete Data
| Radius | 3.206 Earth radii (0.286 Jupiter radii) |
|---|---|
| Orbital period | 29.63 days |
| Earth Similarity Index | 0.26 |
| Distance from Earth | 814.5 light-years (249.7 parsecs) |
| Constellation | Aquarius |
| 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 K2-172 c
Is K2-172 c habitable?
K2-172 c is not known to orbit within the habitable zone of K2-172, and as a sub-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-172 c?
K2-172 c is about 815 light-years from Earth in the constellation Aquarius. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 14,335,200 years to get there.
How big is K2-172 c compared to Earth?
K2-172 c has 3.21 times the radius of Earth.
How long is a year on K2-172 c?
One orbit around K2-172 takes 29.6 Earth days — short enough that 12 of its years would fit into one Earth year.
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