K2-73 b
K2-73 b is a mini-Neptune orbiting K2-73 in the constellation Aquarius. It lies about 878 light-years from Earth and was discovered in 2016 using the transit method.
How Big Is K2-73 b?
K2-73 b has a radius of 2.58 times that of Earth. Its mass is 9.2 times that of Earth, giving it a density of 2.80 g/cm³ — between that of rocky and gaseous planets.
Is K2-73 b in the Habitable Zone?
The position of K2-73 b 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.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Temperature on K2-73 b
The equilibrium temperature of K2-73 b is about 968 K (695 °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 209 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-73 b — one full orbit around K2-73 — lasts 7.50 Earth days, shorter than Mercury's 88-day year.
How Was K2-73 b Discovered?
K2-73 b was discovered in 2016 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 K2-73 b?
K2-73 b 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.
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. K2-73 b scores 0.24, ranking #3,333 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
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 b is one of 2 known planets in the K2-73 system. Its siblings:
- K2-73 c (Cold Gas Giant)
K2-73 b — Complete Data
| Radius | 2.580 Earth radii (0.230 Jupiter radii) |
|---|---|
| Mass | 9.20 Earth masses (0.029 Jupiter masses) |
| Density | 2.80 g/cm³ (Earth: 5.51) |
| Orbital period | 7.50 days |
| Equilibrium temperature | 968 K (695 °C) |
| Stellar irradiation | 209.00× Earth |
| Earth Similarity Index | 0.24 |
| Distance from Earth | 878.0 light-years (269.2 parsecs) |
| Constellation | Aquarius |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2025-09-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-73 b
Is K2-73 b habitable?
K2-73 b is not known to orbit within the habitable zone of K2-73, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-73 b?
K2-73 b 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 big is K2-73 b compared to Earth?
K2-73 b has 2.58 times the radius of Earth and about 9.2 times its mass.
How long is a year on K2-73 b?
One orbit around K2-73 takes 7.5 Earth days — short enough that 49 of its years would fit into one Earth year.
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