HD 128717 b
HD 128717 b is a exoplanet orbiting HD 128717 in the constellation Draco. It lies about 240 light-years from Earth and was discovered in 2025 using the astrometry method.
Is HD 128717 b in the Habitable Zone?
HD 128717 b orbits beyond the outer edge of the habitable zone of HD 128717. At that distance, any surface water would almost certainly be frozen.
Habitable zone of HD 128717: 1.059–2.471 AU (conservative: 1.341–2.342 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 128717 b — one full orbit around HD 128717 — lasts 3,420.0 Earth days, longer than an Earth year. It orbits at an average distance of 4.850 AU. Its orbit is highly elliptical (eccentricity 0.85), swinging dramatically closer to and farther from its star.
How Was HD 128717 b Discovered?
HD 128717 b was discovered in 2025 using the astrometry method, with observations from European Space Agency (ESA) Gaia Satellite.
Astrometry detects a planet by measuring the tiny periodic shift in a star's position on the sky as the star and planet orbit their common center of mass.
How Far Away Is HD 128717 b?
HD 128717 b is 240.2 light-years (73.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1786. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,227,520 years to make the journey.
The Host Star: HD 128717
HD 128717
- Surface temperature
- 6,210 K (Sun: 5,772 K)
- Mass
- 1.21 M☉
- Radius
- 1.25 R☉
- Luminosity
- 2.0989 L☉
- Age
- 1.4 billion years (Sun: 4.6)
Planetary System
HD 128717 b is the only planet known to orbit HD 128717 so far.
HD 128717 b — Complete Data
| Mass | 6,293.00 Earth masses (19.800 Jupiter masses) |
|---|---|
| Orbital period | 3,420.00 days |
| Orbital distance | 4.850 AU |
| Eccentricity | 0.850 |
| Distance from Earth | 240.2 light-years (73.6 parsecs) |
| Constellation | Draco |
| Discovery method | Astrometry |
| Discovery facility | European Space Agency (ESA) Gaia Satellite |
| Discovery year | 2025 |
Data: NASA Exoplanet Archive, last updated 2026-01-08. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 128717 b
Is HD 128717 b habitable?
No — HD 128717 b orbits outside the habitable zone of HD 128717 and is likely too cold for liquid water on its surface.
How far away is HD 128717 b?
HD 128717 b is about 240 light-years from Earth in the constellation Draco. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,227,520 years to get there.
How long is a year on HD 128717 b?
One orbit around HD 128717 takes 3,420.0 Earth days.
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