The Necessity of Cosmic DesignBack in my younger years when I was an atheist and arguing that the cosmos had to be an accident, one of my suggestions was that there is too much waste in the cosmos to believe that any being with intelligence and purpose could have created it. "All you need is the sun and the earth," I said. "All the rest of the creation is superfluous fluff." As the years have gone by and I have become better educated, I have realized that what I called "fluff" is vital to our survival. We now know that the tilt of the earth on its axis is only possible because of the moon.1 The stability of the elliptical orbit of the earth around the sun is only possible because of the effects of the other objects in the solar system.
As astronomers search the galaxy for other solar systems, more and more factors are being found which are directly related to the ability of a planet to sustain life. New data from studies of galaxies and star systems are also showing us that the complexity of life supporting planetary systems is far greater than anyone imagined even a few years ago. In simple terms, there are two things that must exist--the right material to produce and sustain life and protection from those things that would destroy life. Both of these are more difficult to achieve than anyone would have imagined even five years ago.
GHZ is an abbreviation for galactic habitable zone. It has been known for a long time that certain regions of our galaxy could not sustain a stable solar system capable of supporting any kind of life. The cores of galaxies contain black holes and areas of enormous energy outbursts that would produce too much instability for the stability necessary for life to exist. As new studies are being released concerning planets orbiting other stars, it is becoming obvious that something called metallicity is critical to being able to produce life and the places where it can exist. Metallicity is the ratio of metal atoms to hydrogen atoms in a star. Metallicity determines whether planets can exist, what size planets can form, and what their properties will be. Every star that a planet has been found going around has a metallicity close to our sun, and no planets have been discovered around any star with 25% of the value of the sun or lower. Recent studies of our Milky Way show that only 2% of the stars in our galaxy possesses metal richness that would allow planets to form.2 Each of the 67 planets that have been found orbiting other stars are orbiting metal-rich stars.3 High metallicity will also prevent a life-sustaining planet from existing due to stronger gravity, more volatile compounds, and more interference between stars.
The interesting thing is that studies of the Milky Way and of other galaxies show that metallicity varies in the different parts of galaxies. Moving out from the cores of galaxies, metallicity decreases at about 17% every 14,000 light years. This means that the part of the galaxy where the materials would exist to produce life and a planet to put it on is extremely small. Studies of globular clusters which have stars with metallicities of about 25% have not found any planets at all.
Having the right materials is only half of the GHZ story. The other part of the story is being protected from dangerous objects in space. Galactic nuclei, super novas, gamma ray bursts, and black holes all hold the potential to destroy terrestrial planets and any life that might exist on them. Very high metallicities exist near the cores of galaxies, producing black holes. Some kinds of galaxies have large numbers of gamma ray bursts, making them inhospitable for life. When all of these factors are more fully understood, it is obvious that the GHZ is going to be a very small percentage of the volume of the entire galaxy.
CHZ is an abbreviation for circumsteller inhabitable zone. Like the GHZ, it is the region around a star where a life-supporting planet and where life itself can exist. This concept has been understood longer than the GHZ, but in recent years, more data has shown that the earlier proposals about CHZ were more valid than anyone knew. The earlier proposals were that the CHZ was the zone where liquid water can persist for a very long period of time. As more and more data has been collected, the necessity of water for life to exist has become more and more obvious, and it is now clear that water must exist in the liquid state. Studies of Venus have shown that water will boil off of planets too close to the sun and be lost to space due to not only the closeness of the sun, but also of a runaway greenhouse effect. Planets outside the CHZ will be frozen over and again prevent life forms from being able to survive. Green area is the habitable part.
Studies of planets orbiting other stars have shown the shape of planetary orbits are a major issue. A vast majority of the planets that have been discovered have elliptical orbits that are so eccentric that the planets spend part of their orbit outside the CHZ, part of it inside the CHZ, and a relatively small amount of its orbit in the CHZ. These planets not only could not have life on them, but they would radically alter any other planets that might be in the CHZ.
Over the past 50 years, we have seen many claims that life is abundant in the cosmos, with popularizers like Carl Sagan maintaining numbers in the thousands when referring to inhabited planets in our own galaxy. As more data has been obtained, and more has been understood about the dynamics of the solar system and the galaxy, it has become obvious that the conditions needed to have a planet that can sustain life are very hard to come by. The miracle of the planet Earth is just that--a miracle. Our planet is not one of many places where an accidental series of reactions produced a life-supporting planet and then life itself. Complex life is incredibly rare in the galaxy by all measurements available to us, and that rareness suggests that intelligent purpose and design is part of the process that makes it happen wherever that might be.
1. Neil Comins, What If There Were No Moon (New York: Harper
2. Hugh Ross, "Exotic Life Sites," Facts for Faith, page 22.
--Reference: "Refuges for Life in a Hostile Environment," Guillermo Gonzales, Donald Brownlee, and Peter Ward, Scientific American, October 1, 2002, page 60-67.
--John N. Clayton
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