KELT-18 b
KELT-18 b is a hot Jupiter orbiting the F4 V star KELT-18 in the constellation Ursa Major. It lies about 1,048 light-years from Earth and was discovered in 2017 using the transit method.
How Big Is KELT-18 b?
KELT-18 b has a radius of 17.60 times that of Earth, or 1.57 times the radius of Jupiter. Its mass is 375 times that of Earth, giving it a density of 0.38 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is KELT-18 b in the Habitable Zone?
KELT-18 b orbits inside the inner edge of the habitable zone of KELT-18. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of KELT-18: 1.814–4.201 AU (conservative: 2.298–3.983 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on KELT-18 b
The equilibrium temperature of KELT-18 b is about 2,085 K (1,812 °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 3,152 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on KELT-18 b — one full orbit around KELT-18 — lasts 2.87 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.046 AU — closer to its star than Mercury is to the Sun.
How Was KELT-18 b Discovered?
KELT-18 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-18 b?
KELT-18 b is 1,048.2 light-years (321.4 parsecs) from Earth. Light arriving here tonight left the planet about 1,048 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 18,448,320 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-18 b scores 0.05, ranking #5,257 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: KELT-18
KELT-18 b belongs to a system of 2 stars; it orbits KELT-18.
KELT-18
- Spectral type
- F4 V
- Surface temperature
- 6,670 K (Sun: 5,772 K)
- Mass
- 1.52 M☉
- Radius
- 1.91 R☉
- Luminosity
- 6.4999 L☉
- Age
- 1.9 billion years (Sun: 4.6)
Planetary System
KELT-18 b is the only planet known to orbit KELT-18 so far.
KELT-18 b — Complete Data
| Radius | 17.598 Earth radii (1.570 Jupiter radii) |
|---|---|
| Mass | 375.04 Earth masses (1.180 Jupiter masses) |
| Density | 0.38 g/cm³ (Earth: 5.51) |
| Orbital period | 2.87 days |
| Orbital distance | 0.046 AU |
| Equilibrium temperature | 2,085 K (1,812 °C) |
| Stellar irradiation | 3,152.00× Earth |
| Earth Similarity Index | 0.05 |
| Distance from Earth | 1,048.2 light-years (321.4 parsecs) |
| Constellation | Ursa Major |
| Discovery method | Transit |
| Discovery facility | KELT-North |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2017-04-24. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About KELT-18 b
Is KELT-18 b habitable?
No — KELT-18 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is KELT-18 b?
KELT-18 b is about 1,048 light-years from Earth in the constellation Ursa Major. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 18,448,320 years to get there.
How big is KELT-18 b compared to Earth?
KELT-18 b has 17.60 times the radius of Earth and about 375 times its mass.
How long is a year on KELT-18 b?
One orbit around KELT-18 takes 2.9 Earth days — short enough that 127 of its years would fit into one Earth year.
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