Extreme-class world
KELT-9
The hottest known exoplanet — daytime hotter than most stars (4,600 K).
- Planets
- 1
- Distance
- 666.8 ly
- Host
- B-type
About KELT-9
Discovery
KELT-9 b was discovered in 2017 by the KELT survey (Gaudi et al., Nature) — the hottest known exoplanet, transiting a fast-rotating A0-type star nearly twice as hot as the Sun.
Why it matters
With a dayside near 4,600 K, KELT-9 b is hotter than most stars. Iron and titanium atoms have been detected in vapor form in its atmosphere — the planet is so hot its molecules thermally dissociate.
Current research
Ongoing high-resolution spectroscopy continues to inventory atomic species in KELT-9 b's escaping atmosphere; JWST emission spectroscopy probes the thermal inversion driven by its extreme irradiation.
Comparable to
A gas giant orbiting a blue-white A-type star — its dayside is hotter than a typical K-dwarf and atoms float around as free vapor instead of molecules.
System geometry
At a glance
- Hostname
- KELT-9
- Spectral type
- B9.5-A0
- Distance
- 666.8 ly · 204.46 pc
- Stellar mass
- 2.52 M☉
- Stellar radius
- 2.36 R☉
- Luminosity
- 53.001 L☉
- Effective temp
- 10170 K
- Confirmed planets
- 1
- Habitable zone
- 6.916 – 9.974 AU
Top-down orbital diagram
Orbits to scale within this system. Dashed green = habitable-zone edges.
Planet positions are illustrative (evenly spaced in phase). For live motion see the 3D scene.
The planets
1 confirmed.
Gas giant
KELT-9 b
- Orbit
- 0.035 AU
- Period
- 1.48 days
- Radius
- 21.20 R⊕
- Mass
- 915.35 M⊕
- Eq. temperature
- 4050 K
- Eccentricity
- 0.000
- Discovered
- 2017 · Transit
Compared to our Solar System
Each row shows the closest Solar-System analog by radius (log-space). Earth is pinned at the bottom as the constant frame of reference.
| Planet | Radius (R⊕) | Mass (M⊕) | Orbit (AU) | Period (days) | Eq temp (K) | Solar analog |
|---|---|---|---|---|---|---|
| KELT-9 b | 21.20 | 915.35 | 0.035 | 1.48 | 4050 | Jupiter |
| Earth (reference) | 1.00 | 1.00 | 1.000 | 365.25 | 255 | — |
Research status
◇ JWST observation status
1 planet has confirmed JWST observation time across Cycles 1–3.
- KELT-9 b
JWST programs include transit spectroscopy, thermal phase curves, and direct imaging coronagraph observations depending on planet class.
Discovery timeline
- 2017
KELT-9 b
via Transit
If you liked this
Other systems in the same theme:
51 Pegasi
1 planets · 50.4 ly · G5V
First exoplanet ever found around a sun-like star (1995, Nobel Prize 2019).
HD 209458
1 planets · 157.5 ly · G0 V
First exoplanet seen transiting its star (1999) — atmospheric studies pioneer.
WASP-12
1 planets · 1393.5 ly · G2V
A hot Jupiter being literally devoured by its star — losing 6×10⁹ tonnes/sec.
Experience it
See KELT-9 in interactive 3D
Fly through the system, click any planet, watch orbits play out at 100× speed.
▶ Launch 3D scene