K2-73 c
K2-73 c is a cold gas giant orbiting K2-73 in the constellation Aquarius. It lies about 878 light-years from Earth and was discovered in 2025 using the radial velocity method.
Is K2-73 c in the Habitable Zone?
The position of K2-73 c relative to the habitable zone of K2-73 cannot be precisely determined from the available orbital data.
Habitable zone of K2-73: 0.814–1.914 AU (conservative: 1.031–1.815 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-73 c
The equilibrium temperature of K2-73 c is about 186 K (-87 °C) — well below freezing. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 0.28 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-73 c — one full orbit around K2-73 — lasts 1,000.0 Earth days, longer than an Earth year.
How Was K2-73 c Discovered?
K2-73 c was discovered in 2025 using the radial velocity method, with observations from W. M. Keck Observatory.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is K2-73 c?
K2-73 c is 878.0 light-years (269.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1148. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 15,452,800 years to make the journey.
The Host Star: K2-73
K2-73
- Surface temperature
- 5,867 K (Sun: 5,772 K)
- Mass
- 1.02 M☉
- Radius
- 1.06 R☉
The K2-73 Planetary System
K2-73 c is one of 2 known planets in the K2-73 system. Its siblings:
- K2-73 b (Mini Neptune)
K2-73 c — Complete Data
| Mass (best estimate) | 1,142.00 Earth masses |
|---|---|
| Orbital period | 1,000.00 days |
| Equilibrium temperature | 186 K (-87 °C) |
| Stellar irradiation | 0.28× Earth |
| Distance from Earth | 878.0 light-years (269.2 parsecs) |
| Constellation | Aquarius |
| Discovery method | Radial Velocity |
| Discovery facility | W. M. Keck Observatory |
| Discovery year | 2025 |
Data: NASA Exoplanet Archive, last updated 2025-09-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-73 c
Is K2-73 c habitable?
K2-73 c is not known to orbit within the habitable zone of K2-73, and as a cold gas giant it is an unlikely candidate for life as we know it.
How far away is K2-73 c?
K2-73 c is about 878 light-years from Earth in the constellation Aquarius. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 15,452,800 years to get there.
How long is a year on K2-73 c?
One orbit around K2-73 takes 1,000.0 Earth days.
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