K2-273 b
K2-273 b is a sub-Neptune orbiting K2-273 in the constellation Cancer. It lies about 1,005 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-273 b?
K2-273 b has a radius of 3.05 times that of Earth.
Is K2-273 b in the Habitable Zone?
K2-273 b orbits inside the inner edge of the habitable zone of K2-273. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-273: 0.527–1.266 AU (conservative: 0.667–1.200 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 K2-273 b
The equilibrium temperature of K2-273 b is about 849 K (576 °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.
Orbit and Year Length
A year on K2-273 b — one full orbit around K2-273 — lasts 11.7 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.073 AU — closer to its star than Mercury is to the Sun.
How Was K2-273 b Discovered?
K2-273 b 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 K2-273 b?
K2-273 b is 1,004.9 light-years (308.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1022. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 17,686,240 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. K2-273 b scores 0.22, ranking #3,620 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-273
K2-273
- Surface temperature
- 5,161 K (Sun: 5,772 K)
- Mass
- 0.89 M☉
- Radius
- 0.85 R☉
Planetary System
K2-273 b is the only planet known to orbit K2-273 so far.
K2-273 b — Complete Data
| Radius | 3.050 Earth radii (0.272 Jupiter radii) |
|---|---|
| Orbital period | 11.72 days |
| Orbital distance | 0.073 AU |
| Equilibrium temperature | 849 K (576 °C) |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 1,004.9 light-years (308.1 parsecs) |
| Constellation | Cancer |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2021-09-20. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-273 b
Is K2-273 b habitable?
No — K2-273 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-273 b?
K2-273 b is about 1,005 light-years from Earth in the constellation Cancer. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 17,686,240 years to get there.
How big is K2-273 b compared to Earth?
K2-273 b has 3.05 times the radius of Earth.
How long is a year on K2-273 b?
One orbit around K2-273 takes 11.7 Earth days — short enough that 31 of its years would fit into one Earth year.
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