Ultraviolet Habitable Zones

Ultraviolet Habitable Zones

Two years ago, the discovery of Earth-sized planets around M-dwarf stars generated well-deserved excitement in the astronomical community. These stars comprise more than 75 percent of all main-sequence stars (those generating energy by fusing hydrogen into helium in their cores) and they reside as single stars rather than in multi-star systems. For comparison, Sun-like G stars represent less than eight percent of all stars. The existence of planets around M dwarfs greatly expands the potential life-sites in the universe if any of the planets meet all habitability requirements. However, as I predicted, additional research affirms Earth’s unique capacity to continuously support life.

Planets are deemed life-friendly if certain features fall within a specified (and typically narrow) range known as “habitable zones”. For instance, scientists know the surface temperature of a planet must fall within a narrow range in order for liquid water to exist. This constraint allows one to define a water habitable zone around stars. Although liquid water is a necessary condition for life, it is not sufficient. The amount of ultraviolet (UV) radiation a planet receives also affects its habitability. Naturalistic models typically use UV radiation from the Sun as the energy supply required to drive the chemical reactions related to life’s origins. (Creation models don’t have this requirement.) Yet too much UV radiation destroys the DNA backbone vital to life. Thus, each star also exhibits a UV habitable zone.

A team of Chinese scientists recently determined what kind of stars show an overlap between the water and UV habitable zones.1 Their research demonstrated that the two zones coincide for only a relatively small fraction of stars similar to the Sun. For stars with temperatures below 4,600K (like all M-dwarf stars), the UV habitable zone resides closer to the star than the water habitable zone allows. For stars hotter than 7,100K, the UV habitable zone is located beyond the water habitable zone. Requiring a planet to fall within both habitable zones eliminates over 80 percent of all stars, including all M-dwarfs, as potential sites for discovering extraterrestrial life in the universe.

These results add to the growing body of evidence that Earth uniquely provides a habitat for human life. This idea aligns with the biblical description of God preparing our home planet specifically for that purpose.

  1. Jianpo Guo et al., “Habitable Zones and UV Habitable Zones around Host Stars,” Astrophysics and Space Science 325 (January 2010: 25–30.