HD 27969 b
HD 27969 b is a cold gas giant orbiting the G0 V star HD 27969 in the constellation Perseus. It lies about 222 light-years from Earth and was discovered in 2021 using the radial velocity method. It orbits within the habitable zone of its star — the region where liquid water could exist on a planet's surface.
Is HD 27969 b in the Habitable Zone?
HD 27969 b orbits inside the conservative habitable zone of HD 27969 — the region where a rocky planet could sustain liquid water on its surface. This makes it one of the most interesting known exoplanets in the search for life.
Habitable zone of HD 27969: 1.005–2.356 AU (conservative: 1.272–2.233 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on HD 27969 b
The equilibrium temperature of HD 27969 b is about 261 K (-12 °C) — in a range broadly comparable to Earth, whose equilibrium temperature is 255 K. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 0.76 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on HD 27969 b — one full orbit around HD 27969 — lasts 654.5 Earth days, longer than an Earth year. It orbits at an average distance of 1.552 AU. Its orbit is mildly elliptical (eccentricity 0.18).
How Was HD 27969 b Discovered?
HD 27969 b was discovered in 2021 using the radial velocity method, with observations from Haute-Provence Observatory.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is HD 27969 b?
HD 27969 b is 221.6 light-years (67.9 parsecs) from Earth. Light arriving here tonight left the planet around the year 1805. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,900,160 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 27969 b scores 0.38, ranking #563 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 27969
HD 27969
- Spectral type
- G0 V
- Surface temperature
- 5,966 K (Sun: 5,772 K)
- Mass
- 1.16 M☉
- Radius
- 1.27 R☉
Planetary System
HD 27969 b is the only planet known to orbit HD 27969 so far.
HD 27969 b — Complete Data
| Mass (best estimate) | 1,525.58 Earth masses |
|---|---|
| Orbital period | 654.50 days |
| Orbital distance | 1.552 AU |
| Eccentricity | 0.182 |
| Equilibrium temperature | 261 K (-12 °C) |
| Stellar irradiation | 0.76× Earth |
| Earth Similarity Index | 0.38 |
| Distance from Earth | 221.6 light-years (67.9 parsecs) |
| Constellation | Perseus |
| Discovery method | Radial Velocity |
| Discovery facility | Haute-Provence Observatory |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-07-26. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 27969 b
Is HD 27969 b habitable?
HD 27969 b orbits within the habitable zone of HD 27969, the region where liquid water could exist on a planet's surface. It sits in the conservative habitable zone — the most promising region for habitability. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is HD 27969 b?
HD 27969 b is about 222 light-years from Earth in the constellation Perseus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,900,160 years to get there.
How long is a year on HD 27969 b?
One orbit around HD 27969 takes 654.5 Earth days.
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