HD 154857 b
HD 154857 b is a cold gas giant orbiting the G5 V star HD 154857 in the constellation Ara. It lies about 207 light-years from Earth and was discovered in 2004 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 154857 b in the Habitable Zone?
HD 154857 b orbits within the optimistic habitable zone of HD 154857 — the broader region where liquid water might be possible under favorable atmospheric conditions.
Habitable zone of HD 154857: 1.256–2.973 AU (conservative: 1.591–2.819 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 154857 b — one full orbit around HD 154857 — lasts 408.6 Earth days, longer than an Earth year. It orbits at an average distance of 1.290 AU. Its orbit is highly elliptical (eccentricity 0.46), swinging dramatically closer to and farther from its star.
How Was HD 154857 b Discovered?
HD 154857 b was discovered in 2004 using the radial velocity method, with observations from Anglo-Australian Telescope.
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 154857 b?
HD 154857 b is 206.9 light-years (63.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1820. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,641,440 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 154857 b scores 0.29, ranking #1,766 of 5,565 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 154857
HD 154857
- Spectral type
- G5 V
- Surface temperature
- 5,605 K (Sun: 5,772 K)
- Mass
- 1.72 M☉
- Radius
- 1.76 R☉
The HD 154857 Planetary System
HD 154857 b is one of 2 known planets in the HD 154857 system. Its siblings:
- HD 154857 c (Cold Gas Giant)
HD 154857 b — Complete Data
| Mass (best estimate) | 778.68 Earth masses |
|---|---|
| Orbital period | 408.60 days |
| Orbital distance | 1.290 AU |
| Eccentricity | 0.460 |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 206.9 light-years (63.4 parsecs) |
| Constellation | Ara |
| Discovery method | Radial Velocity |
| Discovery facility | Anglo-Australian Telescope |
| Discovery year | 2004 |
Data: NASA Exoplanet Archive, last updated 2018-09-04. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 154857 b
Is HD 154857 b habitable?
HD 154857 b orbits within the habitable zone of HD 154857, the region where liquid water could exist on a planet's surface. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is HD 154857 b?
HD 154857 b is about 207 light-years from Earth in the constellation Ara. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,641,440 years to get there.
How long is a year on HD 154857 b?
One orbit around HD 154857 takes 408.6 Earth days.
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