HD 18599 b
HD 18599 b is a super-Earth orbiting the K2 V star HD 18599 in the constellation Horologium. It lies about 126 light-years from Earth and was discovered in 2022 using the transit method.
How Big Is HD 18599 b?
HD 18599 b has a radius of 2.60 times that of Earth. Its mass is 24.1 times that of Earth, giving it a density of 7.50 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is HD 18599 b in the Habitable Zone?
HD 18599 b orbits inside the inner edge of the habitable zone of HD 18599. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 18599: 0.474–1.140 AU (conservative: 0.601–1.081 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on HD 18599 b — one full orbit around HD 18599 — lasts 4.14 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.048 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.34), swinging dramatically closer to and farther from its star.
How Was HD 18599 b Discovered?
HD 18599 b was discovered in 2022 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
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 HD 18599 b?
HD 18599 b is 125.8 light-years (38.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1901. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,214,080 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. HD 18599 b scores 0.23, ranking #3,443 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 18599
HD 18599 b belongs to a system of 2 stars; it orbits HD 18599.
HD 18599
- Spectral type
- K2 V
- Surface temperature
- 5,145 K (Sun: 5,772 K)
- Mass
- 0.86 M☉
- Radius
- 0.77 R☉
- Luminosity
- 0.3720 L☉
- Age
- 0.4 billion years (Sun: 4.6)
Planetary System
HD 18599 b is the only planet known to orbit HD 18599 so far.
HD 18599 b — Complete Data
| Radius | 2.600 Earth radii (0.232 Jupiter radii) |
|---|---|
| Mass | 24.10 Earth masses (0.076 Jupiter masses) |
| Density | 7.50 g/cm³ (Earth: 5.51) |
| Orbital period | 4.14 days |
| Orbital distance | 0.048 AU |
| Eccentricity | 0.340 |
| Earth Similarity Index | 0.23 |
| Distance from Earth | 125.8 light-years (38.6 parsecs) |
| Constellation | Horologium |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2022 |
Data: NASA Exoplanet Archive, last updated 2022-11-07. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 18599 b
Is HD 18599 b habitable?
No — HD 18599 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 18599 b?
HD 18599 b is about 126 light-years from Earth in the constellation Horologium. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,214,080 years to get there.
How big is HD 18599 b compared to Earth?
HD 18599 b has 2.60 times the radius of Earth and about 24.1 times its mass.
How long is a year on HD 18599 b?
One orbit around HD 18599 takes 4.1 Earth days — short enough that 88 of its years would fit into one Earth year.
Explore HD 18599 b in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
