A plethora of the Earth-like planet: Ramifications of a Fuzzy World

One primary reason for the formulation of the term Earth-like planet and the search for such planets in the galaxy are due to the fact that life has arisen on such a world. Thus, this search seems justifiable since it is here known what one is looking for. However, the Earth-like concept represents an attempt to set up sharp boundaries for an inhabited planet, even though nature often comes as continua. The analyzes in this work show that the term does not represent a clear cut entity as a general Earth likeness cannot be abstracted. Thus, the complex variation of environment and life means that the singular term Earth-like planet is more appropriately treated as a fuzzy world. Such a fuzzification has the consequence that the term is not only more limited than assumed, it may even be deceptive, as an Earth-like planet on the one hand can be in a segment where it does not seem particularly Earth-like, but still possesses life, but on the other hand can appear very Earth-like but not possess life anyway. An atmosphere can provide a biosignature by being displaced from thermodynamic equilibrium, derived from antagonistic adaptation, in which life as a double edged sword on the one hand continuously makes the external environment less favorable for itself, while on the other hand it increases its capacity to do so. Yet, there is an issue with using this as a search criterion for potentially inhabited worlds, as such planets can give impressions that do not reflect what has gone on, it can even give a ghost biosignature. These novel analyzes do not represent a limitation in the search for Earth-like planets, as the plethora of Earth-like planets shows the possibility that the number of inhabited worlds can be large, but it does represent a limitation in the search for life on such worlds.