K2-99 b
K2-99 b is a hot Jupiter orbiting K2-99 in the constellation Virgo. It lies about 1,694 light-years from Earth and was discovered in 2016 using the transit method.
How Big Is K2-99 b?
K2-99 b has a radius of 11.88 times that of Earth, or 1.06 times the radius of Jupiter. Its mass is 277 times that of Earth.
Is K2-99 b in the Habitable Zone?
K2-99 b orbits inside the inner edge of the habitable zone of K2-99. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-99: 2.076–4.857 AU (conservative: 2.630–4.605 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-99 b
The equilibrium temperature of K2-99 b is about 1,184 K (911 °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 K2-99 b — one full orbit around K2-99 — lasts 18.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.153 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.22).
How Was K2-99 b Discovered?
K2-99 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 K2-99 b?
K2-99 b is 1,693.5 light-years (519.2 parsecs) from Earth. Light arriving here tonight left the planet about 1,694 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 29,805,600 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. K2-99 b scores 0.08, ranking #4,706 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-99
K2-99
- Surface temperature
- 6,069 K (Sun: 5,772 K)
- Mass
- 1.44 M☉
- Radius
- 2.55 R☉
- Luminosity
- 7.9299 L☉
- Age
- 3.7 billion years (Sun: 4.6)
The K2-99 Planetary System
K2-99 b is one of 2 known planets in the K2-99 system. Its siblings:
- K2-99 c (Cold Gas Giant)
K2-99 b — Complete Data
| Radius | 11.882 Earth radii (1.060 Jupiter radii) |
|---|---|
| Mass | 276.51 Earth masses (0.870 Jupiter masses) |
| Orbital period | 18.25 days |
| Orbital distance | 0.153 AU |
| Eccentricity | 0.220 |
| Equilibrium temperature | 1,184 K (911 °C) |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 1,693.5 light-years (519.2 parsecs) |
| Constellation | Virgo |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2025-02-24. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-99 b
Is K2-99 b habitable?
No — K2-99 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-99 b?
K2-99 b is about 1,694 light-years from Earth in the constellation Virgo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 29,805,600 years to get there.
How big is K2-99 b compared to Earth?
K2-99 b has 11.88 times the radius of Earth and about 277 times its mass.
How long is a year on K2-99 b?
One orbit around K2-99 takes 18.2 Earth days — short enough that 20 of its years would fit into one Earth year.
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