Among the approximately earth-great planets there are still a number of planets which have a mass of earth about the size of the earth and which have a certain similarity to the earth in the orbit time around their central star, as well as in the rotation time. Such planets are referred to here as approximately earth-like planets.

According to the "Habitable Exoplanets Catalog" of September 2015, 4 out of 10 habitable planets about the size of the earth can be described as distant earth-like.
This corresponds to a share of 40 %. The probability factor is F_a = 0.4 = 2:5.

According to the "Habitable Exoplanets Catalog" of December 2017, 5 of 13 selected habitable planets about the size of the Earth can be described as distant earth-like.
This corresponds to a share of 38.4 %. The probability factor is F_a = 0.384,615 = 5:13.

If you calculate the mean value from both information, you get:

hen equation 2.4.2 can be used to extrapolate a relationship for approximately earth-like planets
Related to all star systems A in our galaxy, the number N_ha of the solar-like star systems, with habitable, approximately earth-like planets, results to:

Starting point are 100-300 billion solar systems, in the galaxy, and inserting into equation 2.5.2 provides:

The probability for habitable, approximately earth-like planets, in solar-like star systems, in the galaxy, is then:

F_ha = F_sph·F_g·F_a
F_ha= 1:15,000 · 1,212:3,286 · 51:130
F_ha= 1:103,664


As a result, only about every 103,664th sun-like star system produces a approximately earth-like planet in the habitable zone.