
If only the
planets are considered, an equation for the
probability of a habitable planet can be
established in any star system. [2] 


8.2.1 Definition 
F_{ph}
= F_{p}
· F_{h} 
So you can use the rounded values.
F_{ph} = 201:14,000 · 10:603
F_{ph}
= 1:4200
Among 4200 star systems there is probably one that has
planets, at least one of which is a habitable planet.
Then applies to the set of all star systems of a spectral
class that possess habitable planets:
8.2.2 Equation 
N_{phx}
= N_{X }·
F_{ph
}N_{phx}
= A · F_{X }·
F_{ph} 
It is important here that all
factors can be determined in the long term by appropriate
instruments of observation, i.e. empirically. According
to theorem 6.1.2, this should be the case in the next two
centuries.
The set of all star systems N_{phxGal}
in the galaxy, with planets and at least one in the
habitable zone, is then the sum of all spectral classes:

N_{phxGal}
= ∑ N_{phx}
= ∑ (A · F_{X }·
F_{ph}) 
Since A remains the same for all
spectral classes, A can be taken from
the sum:
8.2.3 Equation 
N_{phxGal}
= ∑ N_{phx}
= A · ∑ (F_{X }·
F_{ph}) 
Strictly speaking, the
probabilities F_{p} and F_{h} and thus F_{ph}
would have to be determined individually for each
spectral class.
However, since this is not yet possible, a rough
calculation or maximum estimate can be achieved by
assuming the same or similar frequencies of the planetary
distributions in the spectral classes in a first
approach.
If one assumes, in a first assumption, that other star
systems, i.e. not sunlike stars, also have the same or
similar planetary distribution, one can calculate how
many systems could exist with habitable planets at most.
8.2.4 Approach 
In star systems that are not
sunlike, there are probably the same or similar
distributions, for habitable planets, as in
sunlike systems. 
Provided that F_{p} and F_{h}
remain the same for all spectral classes (approach
8.2.4), they can also be drawn from the sum (equation
8.2.3):

N_{phxGal}
= ∑ N_{phx}
= A· F_{ph}
· ∑ (F_{X}) 
The sum of all spectral classes
(for the probabilities F_{X})
results in the totality of the stars in the galaxy:
This results approximately from the
approach 8.2.4:
8.2.5 Equation 
N_{phxGal}
≈ A · F_{ph} 
Starting point are 100300 billion
solar systems, in the galaxy, and inserting all values
into equation 8.2.5 results:
8.2.6 Theorem 
The
quantity of all star systems in the galaxy with
planets and at least one in the habitable zone is
probably a maximum of 23.81 to 71.428 million. 
