Kapteyn b

Kapteyn b[1][2]
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
Distance12.8 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
Database references
Extrasolar Planets
Encyclopaedia		data
SIMBADdata
Exoplanet Archivedata
Open Exoplanet Cataloguedata

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.[2] 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.[3]

The system itself is estimated to be 11 billion years old, substantially older than the Solar System.[2]

Characteristics

Mass, radius, and temperature

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.

Host star

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[4] and has a surface temperature of 5778 K.[5]

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.

Orbit

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.

Habitability

The exoplanet was announced to orbiting in the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. Kapteyn b has a radius range of 1.2–1.6 R⊕, so it is likely rocky. Its host star is a red subdwarf, with a little more than a quarter as much mass then the Sun does. As a result, stars like Kapteyn's Star have the ability to live up to 100–200 billion years, 10–20 times longer than the Sun will live.[6]

Another crucial factor in habitability is temperature and atmospheric properties. The estimated equilibrium temperature for Kapteyn b is around 205 K (−68 °C; −91 °F), too cold to support liquid water on the surface. Without the proper greenhouse gases in its atmosphere (if it has one), it is likely to be a planet covered in ice. However, if it has enough CO2 in its atmosphere, the surface temperature may rise enough to have water exist in its liquid form on the surface.

Discovery

The planet was first discovered by the HARPS spectrometer which is housed at the European Southern Observatory's La Silla Observatory in Chile. Further confirmations of the planetary detection were made at the Keck Observatory in Hawaii and at the PFS Observatory, also in Chile.[2] The method of discovery involved observing and recording tiny wobbles in the star caused by the gravitational tug of its planets, using Doppler spectroscopy.[2]

Additional planet

One other planet has been detected within the same planetary system. It is designated "Kapteyn c" and orbits further out from the star, beyond the outer edge of the habitable zone.[2] It is considered to be too cold for stellar-light based life.[2]

See also

References

  1. ↑ Anglada-Escude, G.; et al. (8 July 2014). "Two planets around Kapteyn's star: a cold and a temperate super-Earth orbiting the nearest halo red dwarf". Oxford Journals. Bibcode:2014MNRAS.443L..89A. arXiv:1406.0818 Freely accessible. doi:10.1093/mnrasl/slu076. Retrieved 10 January 2015.
  2. 1 2 3 4 5 6 7 Wall, Mike (3 June 2014). "Found! Oldest Known Alien Planet That Might Support Life". Space.com. Retrieved 10 January 2015.
  3. ↑ Robertson, Paul (11 May 2015). "Stellar activity mimics a habitable-zone planet around Kapteyn's star". arXiv:1505.02778 Freely accessible.
  4. ↑ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
  5. ↑ Fraser Cain (September 15, 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  6. ↑ Adams, Fred C.; Laughlin, Gregory; Graves, Genevieve J. M. "Red Dwarfs and the End of the Main Sequence". Gravitational Collapse: From Massive Stars to Planets. Revista Mexicana de Astronomía y Astrofísica. pp. 46–49. Bibcode:2004RMxAC..22...46A.

Coordinates: 05h 11m 40.58s, +45° 01′ 06.3″

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