KELT-9 b
KELT-9 b is a hot Jupiter orbiting the B9.5-A0 star KELT-9 in the constellation Cygnus. It lies about 667 light-years from Earth and was discovered in 2017 using the transit method.
How Big Is KELT-9 b?
KELT-9 b has a radius of 21.20 times that of Earth, or 1.89 times the radius of Jupiter. Its mass is 915 times that of Earth, giving it a density of 0.53 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is KELT-9 b in the Habitable Zone?
The position of KELT-9 b relative to the habitable zone of KELT-9 cannot be precisely determined from the available orbital data.
Temperature on KELT-9 b
The equilibrium temperature of KELT-9 b is about 4,050 K (3,777 °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 44,900 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on KELT-9 b — one full orbit around KELT-9 — lasts just 35.5 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.035 AU — closer to its star than Mercury is to the Sun.
How Was KELT-9 b Discovered?
KELT-9 b was discovered in 2017 using the transit method, with observations from KELT-North.
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 KELT-9 b?
KELT-9 b is 666.8 light-years (204.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1360. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 11,735,680 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. KELT-9 b scores 0.04, ranking #5,313 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: KELT-9
KELT-9 b belongs to a system of 2 stars; it orbits KELT-9.
KELT-9
- Spectral type
- B9.5-A0
- Surface temperature
- 10,170 K (Sun: 5,772 K)
- Mass
- 2.52 M☉
- Radius
- 2.36 R☉
- Luminosity
- 53.0005 L☉
- Age
- 0.3 billion years (Sun: 4.6)
Planetary System
KELT-9 b is the only planet known to orbit KELT-9 so far.
KELT-9 b — Complete Data
| Radius | 21.196 Earth radii (1.891 Jupiter radii) |
|---|---|
| Mass | 915.35 Earth masses (2.880 Jupiter masses) |
| Density | 0.53 g/cm³ (Earth: 5.51) |
| Orbital period | 1.48 days |
| Orbital distance | 0.035 AU |
| Equilibrium temperature | 4,050 K (3,777 °C) |
| Stellar irradiation | 44,900.00× Earth |
| Earth Similarity Index | 0.04 |
| Distance from Earth | 666.8 light-years (204.5 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | KELT-North |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2017-06-02. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About KELT-9 b
Is KELT-9 b habitable?
KELT-9 b is not known to orbit within the habitable zone of KELT-9, and as a hot Jupiter it is an unlikely candidate for life as we know it.
How far away is KELT-9 b?
KELT-9 b is about 667 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 11,735,680 years to get there.
How big is KELT-9 b compared to Earth?
KELT-9 b has 21.20 times the radius of Earth and about 915 times its mass.
How long is a year on KELT-9 b?
One orbit around KELT-9 takes 1.5 Earth days — short enough that 247 of its years would fit into one Earth year.
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