HD 128356 b
HD 128356 b is a cold gas giant orbiting the K3 V star HD 128356 in the constellation Hydra. It lies about 85 light-years from Earth and was discovered in 2016 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 128356 b in the Habitable Zone?
HD 128356 b orbits inside the conservative habitable zone of HD 128356 — 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 128356: 0.473–1.149 AU (conservative: 0.599–1.089 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 128356 b — one full orbit around HD 128356 — lasts 298.2 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.870 AU — comparable to the inner Solar System. Its orbit is highly elliptical (eccentricity 0.57), swinging dramatically closer to and farther from its star.
How Was HD 128356 b Discovered?
HD 128356 b was discovered in 2016 using the radial velocity method, with observations from Multiple Observatories.
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 128356 b?
HD 128356 b is 85.3 light-years (26.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1941. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,501,280 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. HD 128356 b scores 0.36, ranking #703 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 128356
HD 128356
- Spectral type
- K3 V
- Surface temperature
- 4,875 K (Sun: 5,772 K)
- Mass
- 0.65 M☉
- Radius
- 0.85 R☉
- Luminosity
- 0.3600 L☉
- Age
- 10.0 billion years (Sun: 4.6)
Planetary System
HD 128356 b is the only planet known to orbit HD 128356 so far.
HD 128356 b — Complete Data
| Mass (best estimate) | 282.87 Earth masses |
|---|---|
| Orbital period | 298.20 days |
| Orbital distance | 0.870 AU |
| Eccentricity | 0.570 |
| Earth Similarity Index | 0.36 |
| Distance from Earth | 85.3 light-years (26.2 parsecs) |
| Constellation | Hydra |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2016-11-09. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 128356 b
Is HD 128356 b habitable?
HD 128356 b orbits within the habitable zone of HD 128356, 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 128356 b?
HD 128356 b is about 85 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,501,280 years to get there.
How long is a year on HD 128356 b?
One orbit around HD 128356 takes 298.2 Earth days.
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