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HD 106315

K2-109

A faint F-type bright yellow star, HD 106315 lies westward of Zaniah or Eta Virginis, close to the line of the Ecliptic as it runs through Virgo. At ninth magnitude, the star is much too faint to be detected with the naked eye. HD 106315 is a dwarf star, somewhat larger, hotter and more luminous than the Sun (it is estimated to be some 1.5 times the Sun's diameter, and 3.7 times more luminous). By comparison with the Sun, it is also relatively lacking in heavier elements ('metals' in this context). According to parallax measurements, HD 106315 lies some 356 light years from the Solar System.

Imagery provided by Aladin sky atlas

HD 106315 is notable for its possession of planetary system consisting of two, and quite possibly three, planets. Two of these are confirmed to be large and massive planets in close orbits of the star (both orbit well within the distance of Mercury from the Sun). The innermost, HD 106316 b, is more than ten times the mass of Earth and twice its diameter, and is typcially classified as a 'super Earth' (though it is not known whether or not it has a solid surface). The outermost - while still in an extremely close orbit of the star - is HD 106315 c, which is generally thought to be similar in structure to the ice giants of the Solar System (though, being so close to its star, it is more suitably described as a 'warm Neptune').

Positioned so near to the star HD 106315, these two planets orbit extremely rapidly, with HD 106315 b completing its 'year' in nine days, while HD 106315 c orbits once every twenty-one days. The dynamics of the orbits of these two planets suggest that a third planet, more distant and massive than either of the inner pair, is also to be found within the system, though the existence of this third planet has yet to be confirmed.

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