Kapteyn b
| Exoplanet | List of exoplanets | |
|---|---|---|
| Parent star | ||
| Star | Kapteyn's star | |
| Right ascension | (α) | 05h 11m 40.58s |
| Declination | (δ) | +45° 01′ 06.3″ |
| Apparent magnitude | (mV) | 8.8 |
| Distance | 12.8 ly (3.92±0.01 pc) |
|
| Spectral type | sdM1 | |
| Mass | (m) | 0.274 M☉ |
| Radius | (r) | 0.291±0.025 R☉ |
| Temperature | (T) | 3550±50 K |
| Metallicity | [Fe/H] | −0.99 (± 0.04) |
| Age | ~11 Gyr | |
| Physical characteristics | ||
| Mass | (m) |
4.8+0.9 −1.0 M⊕ |
| Radius | (r) |
1.6+0.41 −0.4 R⊕ |
| Stellar flux | (F⊙) | 0.4 ⊕ |
| Maximum stellar flux | (F⊙max) | 0.69 ⊕ |
| Minimum stellar flux | (F⊙min) | 0.29 ⊕ |
| Temperature | (T) | 205 K (−68 °C; −91 °F) |
| Orbital elements | ||
| Semi-major axis | (a) |
0.168+0.006 −0.008 AU |
| Eccentricity | (e) | 0.21+0.11 −0.10 |
| Orbital period | (P) |
48.616+0.036 −0.032 d |
| Discovery information | ||
| Discovery date | June 2014 | |
| Discoverer(s) | HARPS | |
| Discovery method | Radial velocity | |
| Discovery status | Published refereed article | |
| Other designations | ||
|
HIP 24186 b; 2MASS J05114046-4501051 b; TYC 8078-01749-1 b; IRAS 05100-4502 b; WISE J051146.81-450204.5 b; CPD-44 612 b; SAO 217223 b; GJ 191 b; VZ Pic b; Kapteyn's star b; LHS 29 b; HD 33793 b; CD-45 1841 b
|
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| Database references | ||
| Extrasolar Planets Encyclopaedia |
data | |
| SIMBAD | data | |
| Exoplanet Archive | data | |
| Open Exoplanet Catalogue | data | |
Kapteyn b is a possible exoplanet that orbits within the habitable zone of the red subdwarf Kapteyn's star, located approximately 12.8 light-years (3.92 pc) from Earth. Kapteyn b is within the estimated habitable zone of its star. It was the closest suspected potentially habitable exoplanet to the Solar System other than Tau Ceti e up until 2016, when Proxima Centauri b at 4.22 light-years was confirmed. However, later research has cast doubt on the existence of Kapteyn b, suggesting the signal is consistent with stellar activity rather than a planet.
The system itself is estimated to be 11 billion years old, substantially older than the Solar System.
Kapteyn b, if it exists, is a super-Earth, a planet that has a radius and mass bigger than that of Earth, but smaller than that of the ice giants Uranus and Neptune. It has a surface temperature of 205 K (−68 °C; −91 °F). It has a mass greater than that or equal to 4.8 M⊕ and a radius less than or equal to around 1.6 R⊕, depending on its composition, making it a likely rocky world.
The planet orbits a red subdwarf star named Kapteyn's Star. The star has a mass of 0.27 M☉ and a radius 0.29 R☉. It has a surface temperatures of 3550 K and is roughly 11 billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K.
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 8.85. It is too dim to be seen with the naked eye, but can be seen with good binoculars.
Kapteyn b makes a complete orbit around its parent star with about 1.2% of the Sun's luminosity about every 48.62 days at a distance of 0.17 AU (compared to Mercury, which orbits at a distance of around 0.39 AU. It has an eccentricity of 0.21, meaning its orbit is mildly elliptical.
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