HD 128311 b
HD 128311 b is a cold gas giant orbiting HD 128311 in the constellation Boötes. It lies about 53 light-years from Earth and was discovered in 2002 using the radial velocity method.
Is HD 128311 b in the Habitable Zone?
The position of HD 128311 b relative to the habitable zone of HD 128311 cannot be precisely determined from the available orbital data.
Orbit and Year Length
A year on HD 128311 b — one full orbit around HD 128311 — lasts 453.0 Earth days, longer than an Earth year. It orbits at an average distance of 1.084 AU — comparable to the inner Solar System. Its orbit is highly elliptical (eccentricity 0.30), swinging dramatically closer to and farther from its star.
How Was HD 128311 b Discovered?
HD 128311 b was discovered in 2002 using the radial velocity method, with observations from W. M. Keck 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 128311 b?
HD 128311 b is 53.3 light-years (16.3 parsecs) from Earth. Light arriving here tonight left the planet around the year 1973. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 938,080 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 128311 b scores 0.27, ranking #2,625 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 128311
HD 128311
- Mass
- 0.83 M☉
- Radius
- 0.76 R☉
- Age
- 1.0 billion years (Sun: 4.6)
The HD 128311 Planetary System
HD 128311 b is one of 2 known planets in the HD 128311 system. Its siblings:
- HD 128311 c (Cold Gas Giant)
HD 128311 b — Complete Data
| Mass (best estimate) | 562.24 Earth masses |
|---|---|
| Orbital period | 453.02 days |
| Orbital distance | 1.084 AU |
| Eccentricity | 0.303 |
| Earth Similarity Index | 0.27 |
| Distance from Earth | 53.3 light-years (16.3 parsecs) |
| Constellation | Boötes |
| Discovery method | Radial Velocity |
| Discovery facility | W. M. Keck Observatory |
| Discovery year | 2002 |
Data: NASA Exoplanet Archive, last updated 2015-06-24. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 128311 b
Is HD 128311 b habitable?
HD 128311 b is not known to orbit within the habitable zone of HD 128311, and as a cold gas giant it is an unlikely candidate for life as we know it.
How far away is HD 128311 b?
HD 128311 b is about 53 light-years from Earth in the constellation Boötes. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 938,080 years to get there.
How long is a year on HD 128311 b?
One orbit around HD 128311 takes 453.0 Earth days.
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