Читать книгу Planet Formation and Panspermia - Группа авторов - Страница 32

To the limits of our ignorance, it is the level where life manifests itself. The modern habitability models (including galactic ones) have their roots in the concept of the circumstellar habitable zone [4.15]. Our present knowledge on exoplanets implies that there should be a multitude of Earth-like worlds within the habitable zones of their host stars. Their habitability would depend on the stability of orbital configurations, the evolution of the stellar radiation output, their atmospheres, and the possibility of them being impacted by the small bodies that orbit within the stellar system.

Figure 4.1 Sketch of the levels of influences of matter and their inter-relations in regard to panspermia.

Planetary systems can emit panspermia material on their own, during their intrinsic evolution that consists of planetary migrations and behavior of asteroid belts. However, this is likely to take place during the early stages of the stellar system’s evolution. Upon depleting the initial reservoirs of small bodies, e.g., such as the possible scenario in TRAPPIST-1 [4.11] and reaching stable planetary configurations, the emissions of this kind are likely to become significantly smaller. However, even such small emissions could be significant over longer time periods, increasing the “background” galactic panspermia potential. This implies an underlying assumption that dormant forms of life, within their carriers, are not affected by the harsh space conditions during these time spans. The nature of such a panspermia process is inherently diffusive and it would likely boost the appearance of life in general. In an epistemological sense, it is similar to an in situ appearance of life, given favorite galactic conditions. On the other hand, sporadic events such as close stellar flybys can perturb planetary systems and increase the emissions of material. As such, they offer a handle to relate the panspermia process to galactic parameters, especially dynamics.