NGTS-18 b
NGTS-18 b is a hot Jupiter orbiting the G5 V star NGTS-18 in the constellation Hydra. It lies about 3,575 light-years from Earth and was discovered in 2021 using the transit method.
How Big Is NGTS-18 b?
NGTS-18 b has a radius of 13.56 times that of Earth, or 1.21 times the radius of Jupiter. Its mass is 130 times that of Earth, giving it a density of 0.28 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is NGTS-18 b in the Habitable Zone?
NGTS-18 b orbits inside the inner edge of the habitable zone of NGTS-18. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of NGTS-18: 0.995–2.354 AU (conservative: 1.260–2.232 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on NGTS-18 b
The equilibrium temperature of NGTS-18 b is about 1,381 K (1,108 °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 845 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on NGTS-18 b — one full orbit around NGTS-18 — lasts 3.05 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.045 AU — closer to its star than Mercury is to the Sun.
How Was NGTS-18 b Discovered?
NGTS-18 b was discovered in 2021 using the transit method, with observations from Next-Generation Transit Survey (NGTS).
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 NGTS-18 b?
NGTS-18 b is 3,575.3 light-years (1,096.2 parsecs) from Earth. Light arriving here tonight left the planet about 3,575 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 62,925,280 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. NGTS-18 b scores 0.07, ranking #4,994 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: NGTS-18
NGTS-18
- Spectral type
- G5 V
- Surface temperature
- 5,610 K (Sun: 5,772 K)
- Mass
- 1.00 M☉
- Radius
- 1.39 R☉
- Age
- 10.8 billion years (Sun: 4.6)
Planetary System
NGTS-18 b is the only planet known to orbit NGTS-18 so far.
NGTS-18 b — Complete Data
| Radius | 13.563 Earth radii (1.210 Jupiter radii) |
|---|---|
| Mass | 129.99 Earth masses (0.409 Jupiter masses) |
| Density | 0.28 g/cm³ (Earth: 5.51) |
| Orbital period | 3.05 days |
| Orbital distance | 0.045 AU |
| Equilibrium temperature | 1,381 K (1,108 °C) |
| Stellar irradiation | 845.00× Earth |
| Earth Similarity Index | 0.07 |
| Distance from Earth | 3,575.3 light-years (1,096.2 parsecs) |
| Constellation | Hydra |
| Discovery method | Transit |
| Discovery facility | Next-Generation Transit Survey (NGTS) |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-04-23. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About NGTS-18 b
Is NGTS-18 b habitable?
No — NGTS-18 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is NGTS-18 b?
NGTS-18 b is about 3,575 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 62,925,280 years to get there.
How big is NGTS-18 b compared to Earth?
NGTS-18 b has 13.56 times the radius of Earth and about 130 times its mass.
How long is a year on NGTS-18 b?
One orbit around NGTS-18 takes 3.1 Earth days — short enough that 120 of its years would fit into one Earth year.
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