I always understood that Population II stars were unlikely to have planets as they were virtually all H and He with very little else.

Have recent observations confirmed this, or have planets been discovered around Population II stars?

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    $\begingroup$ Do you mean Population III stars? Population II stars do have lower metallicity than Population I, but they are by no means devoid of heavier elements. $\endgroup$
    – user24157
    Commented Feb 26, 2020 at 18:24

1 Answer 1


Kapteyn's star has 14% the metallicity of the Sun and is about 11 billion years old and is in the galactic halo. It has two reported planets.

I don't know if 14% is low enough to count as Population II, but according to the NASA exoplanet archive it is the lowest metallicity star known to have planets.

  • $\begingroup$ I seem to recall that below $[Fe/H] \approx -0.3$ stars count as Pop II, so that would include Kapteyn's star. $\endgroup$ Commented Feb 26, 2020 at 20:20
  • $\begingroup$ Its not particularly metal-poor. There is no strict definition, but this would be a borderline case. It is not in the halo, it is only 12 light years from Earth. $\endgroup$
    – ProfRob
    Commented Feb 26, 2020 at 20:56
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    $\begingroup$ According to the article academic.oup.com/mnras/article/350/2/575/1117003 it is a halo star. $\endgroup$
    – sno
    Commented Feb 26, 2020 at 21:14
  • $\begingroup$ It's kinematically a halo star, but is isn't "in the halo". Pedantic possibly, but a lot of readers would misunderstand. The same reference also provides a lower metallicity than your value. $\endgroup$
    – ProfRob
    Commented Feb 26, 2020 at 21:48

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