GEOLOGICAL PROCESSES
able to regulate its temperature. Even if it was located within the bounds of the conventionally defined HZ, the planet’s surface temperature would become too hot and would not be amenable to supporting life.
Discussion
The incorporation of geological, planet-specific factors into an evaluation of the HZ provides a broader insight into this concept that can alter and more tightly focus the scope and direction of extraterrestrial investigations into the search for life. Health and Doyle (2014) have suggested an “Ecospheres” approach, for example. Looking holistically at geological and other factors that contribute to the availability of liquid water may identify a wider variety of planets that are capable of supporting life, even where the orbits of those planets lie far outside the inner or outer bounds of the HZ associated with the respective host stars. These planets may contain self-sustaining ecosystems independent of the temperature restrictions associated with the respective distance from a star (Kane, 2014). These specialty ecosystems may have evolved on snowball worlds, densely-atmosphered worlds made from unconventional gases, or even tidally-locked planets (one side in perpetual starlight and another in perpetual darkness) that revolve around M-dwarf (small, cool) stars.
While an important and significant starting point, defining the Habitable Zone goes beyond the traditional analysis of Kasting et al. (2014). It is not sufficient to infer a planet’s abil- ity to sustain liquid water or define its breadth of habitability based solely on its distance from a star. The contributions of complex geological processes are significant in determin- ing whether or not a planet can support not only water but also biological activity. Considering the suggested 17 billion Earth-sized worlds that exist in just our galaxy alone, it seems reasonable for astrophysicists to seek some simple means of isolating the potential for extraterrestrial life (Rushby, 2013). The concept of the Habitable Zone will continue to be a useful starting point, but over time likely will need to evolve into a more sophisticated and broadly encompassing tool that includes geologic and other planet-specific processes. As the HZ tool and our knowledge evolves, our understanding of and efficiency at exploring for life will increase and eventually be determinative.
Acknowledgement
The author wishes to thank Bob Blauvelt (CPG 6508), course instructor for Introduction to Geophysics at NYU Poly, for his review of this paper.
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Jerome Scelza is currently studying Mechanical Engineering and Nuclear Physics at New York University. He has always aspired to contribute to the physical sciences. With a natural ability for hands on application and a founda- tion in engineering he hopes to provide an applied component to research in the more pure sciences.
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