Probabilities in the Galaxy


A Distribution Model for habitable Planets

Copyright © Klaus Piontzik
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2.4.1 - Comment on press releases

In the press you can read headlines like "Billions of habitable planets in the Milky Way" (spiegel.de) or "Every second star with an Earth twin?" (Scinexx.de). But all of these are just headlines from greedy journalists and are actually not correct. Already when reading the article it is striking that the authors then backtrack to a large extent and then there are numbers that are considerably smaller than propagated in the headline.

These articles usually refer to the investigation by Erik Petigura in the PNAS and the statement that a maximum of 22% of the G-star systems could have Earth-sized planets in the habitable zone. The number of G-star systems in the galaxy is 28 to 84 billion. 22% of these are 6.2 to 18.5 billion G-systems with habitable planets about the size of Earth. However, this number is then declared as “earth-like” or even “habitable” and that is not possible at all due to the information available and is therefore not permitted !!! The size categories are not taken into account here. In the PHL categorization, planets that are actually only about the size of an Earth are referred to as Terrans or Earth-like. This is actually somewhat misleading because it induces Terrans = "Earth 2". That's not the case!!!

In order to avoid misunderstandings and confusion, the categories Terran great and Terran like and Terran earth were introduced in Chapter 1.8.

In the PHL categorization: Terrans (earth-like)
In the new decoration: Terran great (approximately earth-great planets)

Terran like (approximately earth-like Planets)
Terran earth (Earth 2)

The mistake made in the press is to equate roughly earth-sized planets with earth-like or "earth 2" and thus (potentially) habitable planets. It is not possible to infer earth-like planets from the available information, and certainly not whether they are habitable. Therefore, such maximum information as in the press releases is inadmissible and misleading or wild speculation.

The maximum estimates made here are based on well-founded data and are far from being as high as with the press. So far, there have been several options, e.g. 15 times, 31 times, 60 times the values ??from the model seem to be possible. According to the "Habitable Exoplanets Catalog" from July 2018, a total of 18.5% of all exoplanets are roughly Earth-sized. According to Erik Petigura, 23 3% of the sun-like stars in the galaxy have an Earth-sized planet. Both statements do not take into account the habitability, so it is unlikely that the same occurrence rate will apply to habitable earth-sized planets.


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 Probabilities in the Galaxy

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176 sides, of them 64 in Color
76 pictures
11 tables

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ISBN 9-783-7528-5524-1

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The Autor - Klaus Piontzik