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HD 138573 is G-type main-sequence star in the constellation Serpens, class G5IV-V, roughly 100.8 light years from Earth (30.912 parsecs). Though a G type star like the Sun, a 2005 study found that it is not a solar twin as HD 138573 has a much lower mass, lower metallicity, and is much older age than the Sun at 5.6 billion years old. HD 138573 is otherwise close to the Sun's characteristics and could be classed as a Solar analog.
Sun comparison
This chart compares the Sun to HD 138573.
To date no solar twin with an exact match as that of the Sun has been found, however, there are some stars that come very close to being identical to that of the Sun, and are such considered solar twins by the majority of the public. An exact solar twin would be a G2V star with a 5,778K temperature, be 4.6 billion years old, with the correct metallicity and a 0.1% solar luminosity variation. Stars with an age of 4.6 billion years are at the most stable state. Proper metallicity and size are also very important to low luminosity variation.