HD 4203 b
HD 4203 b is a cold gas giant orbiting HD 4203 in the constellation Pisces. It lies about 265 light-years from Earth and was discovered in 2001 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 4203 b in the Habitable Zone?
HD 4203 b orbits within the optimistic habitable zone of HD 4203 — the broader region where liquid water might be possible under favorable atmospheric conditions.
Habitable zone of HD 4203: 1.010–2.393 AU (conservative: 1.280–2.269 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Orbit and Year Length
A year on HD 4203 b — one full orbit around HD 4203 — lasts 431.9 Earth days, longer than an Earth year. It orbits at an average distance of 1.170 AU. Its orbit is highly elliptical (eccentricity 0.52), swinging dramatically closer to and farther from its star.
How Was HD 4203 b Discovered?
HD 4203 b was discovered in 2001 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 4203 b?
HD 4203 b is 265.4 light-years (81.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1761. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,671,040 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 4203 b scores 0.37, ranking #655 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 4203
HD 4203
- Surface temperature
- 5,596 K (Sun: 5,772 K)
- Mass
- 1.25 M☉
- Radius
- 1.42 R☉
The HD 4203 Planetary System
HD 4203 b is one of 2 known planets in the HD 4203 system. Its siblings:
- HD 4203 c (Cold Gas Giant)
HD 4203 b — Complete Data
| Mass (best estimate) | 708.76 Earth masses |
|---|---|
| Orbital period | 431.88 days |
| Orbital distance | 1.170 AU |
| Eccentricity | 0.520 |
| Earth Similarity Index | 0.37 |
| Distance from Earth | 265.4 light-years (81.4 parsecs) |
| Constellation | Pisces |
| Discovery method | Radial Velocity |
| Discovery facility | W. M. Keck Observatory |
| Discovery year | 2001 |
Data: NASA Exoplanet Archive, last updated 2018-09-04. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 4203 b
Is HD 4203 b habitable?
HD 4203 b orbits within the habitable zone of HD 4203, 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 4203 b?
HD 4203 b is about 265 light-years from Earth in the constellation Pisces. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,671,040 years to get there.
How long is a year on HD 4203 b?
One orbit around HD 4203 takes 431.9 Earth days.
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