A first estimate
for the probability factor F_{e}
can be developed. CASE 1 The probability of encountering an approximately earthgreat planet in the habitable zone is F_{g} = 0.368,837 = 1,212:3,286. The probability of finding an approximately earthlike planet is F_{a} = 0.392,3 = 51:130. The probability for a second earth could be in the same order of magnitude. The probability of a second earth is therefore set at a maximum of 30 %. The probability factor is therefore F_{e1 }= 0.3 = 3:10. The probability of finding an "Earth 2" among habitable planets is therefore: F_{gae1} = F_{g}·F_{a}·F_{e1} F_{gae1} = 1,212:3,286 · 51:130 · 3:10 F_{gae1} = 0.043,409 = 1:23 That means: Among 23 habitable planets there should be an "Earth 2". So we should have found a second Earth by now. Since this has not yet happened (so far 53 habitable planets are known) the probability F_{e1} = 0.3 is too high and can therefore be omitted in the further considerations. CASE 2 The probability of finding an approximately earthlike planet in the habitable zone can be formulated as follows: F_{e2} = F_{g}·F_{a} F_{e2} = 1,212:3,286 · 51:130 F_{e2} = 0.144,697 = 1:7 The probability of an approximately earthlike planet is 14.46%. The probability for a second earth is therefore chosen at a maximum of 10%. The probability factor is F_{e2} = 0.1 = 1:10. F_{gae2} = F_{g}·F_{a}·F_{e2} F_{gae2} = 1,212:3,286 · 51:130 · 1:10 F_{gae2} = 0.014,469 = 1:69 That means: Among 69 habitable planets an "Earth 2" should be found. Since 53 habitable planets are known, we should therefore be on the verge of finding a second Earth in the next few years. CASE 3 The number of solarlike systems with planets determined by the Kepler telescope is 1.4357 %. The number of suns, with planets, in habitable zones is 1.658 %. The probability of a second earth is therefore chosen at a minimum of 1 %. The probability factor is F_{e3} = 0.01 = 1:100. F_{gae3} = F_{g}·F_{a}·F_{e3} F_{gae3} = 1,212:3,286 · 51:130 · 1:100 F_{gae3} = 0.001,446 = 1:684 Among 684 habitable planets an "Earth 2" should be found. 
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