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Very few such halo stars are located near our solar system, with such stars accounting for only 0.1 to 0.2 percent of all stars that are near the sun. Kapteyn's Star is believed to be the closest of these.  The star is a member of a local cluster of halo stars that is very thinly spread out over a distance of some 6,500 to 9,800 light-years stretching towards the galactic halo.<ref>Eggen, O. (1996). The Ross 451 Group of Halo Stars. ''The Astronomical Journal'', 112, p.2661. [http://adsabs.harvard.edu/abs/1996AJ....112.2661E Online]</ref> Kapteyn's Star is unusual because most such stars lie far above or below the galactic plane. Like other halo stars, Kapteyn's Star does have an extremely [[ellipse|elliptical]] galactic orbit and is believed to be among the oldest stars in the galaxy and the region around it, estimated to be some 10 billion years old or older.

Very few such halo stars are located near our solar system, with such stars accounting for only 0.1 to 0.2 percent of all stars that are near the sun. Kapteyn's Star is believed to be the closest of these.  The star is a member of a local cluster of halo stars that is very thinly spread out over a distance of some 6,500 to 9,800 light-years stretching towards the galactic halo.<ref>Eggen, O. (1996). The Ross 451 Group of Halo Stars. ''The Astronomical Journal'', 112, p.2661. [http://adsabs.harvard.edu/abs/1996AJ....112.2661E Online]</ref> Kapteyn's Star is unusual because most such stars lie far above or below the galactic plane. Like other halo stars, Kapteyn's Star does have an extremely [[ellipse|elliptical]] galactic orbit and is believed to be among the oldest stars in the galaxy and the region around it, estimated to be some 10 billion years old or older.

In October 2009, astronomers observing the group of stars that Kapteyn's star is a member of hypothesized that Kapteyn's Star itself is one of 14 [[halo star]]s that share the same elemental abundance as many stars in the globular cluster [[Omega Centauri]], some 17,000 light years away.<ref>Bekki, K. and Freeman, K. (2005). Formation of ω Centauri from an Ancient Nucleated Dwarf Galaxy. ''Highlights of Astronomy'', 13, p.196. [http://adsabs.harvard.edu/abs/2005HiA....13..196B Online]</ref> Because Omega Centauri has stars of different age groups, it is theorized that it is the core remainder of a dwarf galaxy that since merged with the [[Milky Way]]. Kapteyn's Star may be one of the ancient stars of Omega Centauri perturbed into a retrograde orbit from this galactic merger.<ref>Boer, E., Freeman, K. and Williams, M. (2009). Evidence of Omega Cen tidal debris in the Kapteyn moving group. ''Proceedings of the International Astronomical Union'', 5(S265), pp.263-266. [http://arxiv.org/abs/0910.3735 arXiv:0910.3735]</ref>

In October 2009, astronomers observing the group of stars that Kapteyn's star is a member of hypothesized that Kapteyn's Star itself is one of 14 [[halo star]]s that share the same elemental abundance as many stars in the globular cluster [[Omega Centauri]], some 17,000 light years away.<ref>Bekki, K. and Freeman, K. (2005). Formation of ω Centauri from an Ancient Nucleated Dwarf Galaxy. ''Highlights of Astronomy'', 13, p.196. [http://adsabs.harvard.edu/abs/2005HiA....13..196B Online]</ref> Because Omega Centauri has stars of different age groups, it is theorized that it is the core remainder of a dwarf galaxy that since merged with the [[Milky Way]]. Kapteyn's Star may be one of the ancient stars of Omega Centauri perturbed into a retrograde orbit from this galactic merger.<ref>Boer, E., Freeman, K. and Williams, M. (2009). Evidence of Omega Cen tidal debris in the Kapteyn moving group. ''Proceedings of the International Astronomical Union'', 5(S265), pp.263-266. [https://arxiv.org/abs/0910.3735 arXiv:0910.3735]</ref>

There are no known sub-stellar companions around Kapteyn's Star at this time. However the star is classified as a "Tier 1" target star for [[NASA|NASA's]] optical [[Space Interferometry Mission]] that will search for rocky worlds, due to its proximity to our system. For an [[Earth]]-like world to have liquid water on its surface, the world would have to be around 0.26 [[AU]]s from the star, or about half of [[Mercury|Mercury's]] distance from the sun. Such a world would be tidally locked to the star.<ref name="sol"/>

There are no known sub-stellar companions around Kapteyn's Star at this time. However the star is classified as a "Tier 1" target star for [[NASA|NASA's]] optical [[Space Interferometry Mission]] that will search for rocky worlds, due to its proximity to our system. For an [[Earth]]-like world to have liquid water on its surface, the world would have to be around 0.26 [[AU]]s from the star, or about half of [[Mercury|Mercury's]] distance from the sun. Such a world would be tidally locked to the star.<ref name="sol"/>