God has placed us on a special planet

[David Seargent]

If astronomical science has shown us anything in recent years, it is just how special the Earth is! Although many science textbooks still say that the Earth is “average” and “not special” those astronomers who study the conditions for life in the universe tell a very different story.

Compared with the other rocky planets in our solar system, Earth is very different. It is at just the right distance from the Sun to be not too hot or not too cold, it has a very large moon that acts to stabilize its axis of rotation and it has a relatively thin crust that allows constant release of internal heat through plate tectonics rather than having heat build up over vast ages and erupting in episodes of extreme volcanic activity of the type that seems to have happened on Venus where the entire planet appears to have been flooded with lava and left with a chocking atmosphere. On top of that, the Sun and its retinue of planets (of which Earth in one) are now known to orbit the center of the Galaxy at a very special location. If it was much closer to the core, the density of stars in our region would be higher. But some stars explode in violent thermonuclear catastrophes which would just about sterilize any planet within tens of light years of them (these explosions are known as supernovas). But if the Sun and Earth were too far from the galactic core, there would not be enough of the elements that comprise earth-like planets (this is because the very explosions that make the inner regions of the Galaxy unsafe are also responsible for synthesizing and scattering these elements which then go into the formation of later generations of stars and their attendant planets). But even more than this, the Galaxy is crossed by spiral patterns of bright stars which sweep around the Galaxy along the crests of density waves. Photographs of other galaxies like our own show these as very pretty patterns, but in reality they are dangerous places to be. The bright stars marking them out, along with many other smaller ones, form along the crests of these density waves, but the bright stars are so vigorous that they do not last long and (whereas the smaller and longer-lived ones eventually scatter beyond the spiral patterns) blow up whilst still within the spiral patterns. The spiral patterns, being waves, are not actually orbiting the galactic core as the stars are. In fact, the stars closer to the core orbit faster than the spiral patterns while those in the outer regions go slower. In either case, both populations of stars periodically pass through the spiral patterns and, in so doing, are in danger of being too close to one of the bright stars when it explodes as a supernova. Not only that, but the Sun (and many other stars presumably) are surrounded at great distances by clouds of tens or hundreds of billions of comets, so far out that they are only just held in orbit by gravity. If the Sun passed through a spiral pattern, the higher density of material within the spiral would cause many of these to fall inward and not a few would strike the inner planets, including Earth. Moreover, there are probably many more within the spirals that have been tossed out of other star systems and maybe even a number that have always floated free within the spiral. In any event, between nearby supernova and in-falling comets, Earth would be in for a rough time!

However, the Sun is found to be orbiting the galactic core at a region called the corotation radius. In short, this is a narrow zone where the orbital velocity of a star matches that of the density wave. Furthermore, the Sun is located between the spiral patterns, so it simply orbits the galactic core in a safe region – rather like a ship sailing in the eye of a hurricane remains safe if its speed matches that of the hurricane itself! In our Galaxy, this corotation circle lies within the zone favorable to life, but there is no reason why that should be so and a study of other galaxies suggests that it may not be the case in many of these objects.

But, if all of this is not enough, it now seems that our Galaxy itself is rather special too! Very large galaxies like ours typically grow through the merging of several smaller ones. However, in most instances one or more of these “smaller” galaxies is still quite large and its merger may well disrupt the orbits of many stars within the primary one (forcing the Sun out of its orbit near the corotation circle for instance). But it seems that our Galaxy grew from the merger of many small galaxies rather than a few large ones. One consequence of this is the orbital stability of the Sun. Another is the relatively small size of the black hole at the galactic core. Galaxies are known to have supermassive black holes at their cores, but the one in our galaxy (although still supermassive) is a lot smaller than is normal for so large a galaxy. When galaxies merge, their central black holes will also merge eventually, so the fact that only small galaxies merged into our own means that the central black hole remains undersized. Although this research is very new, it does appear that galaxies with very large central black holes contain lower amounts of the heavy elements required for the building of earth-like planets. Central black holes draw in a lot of matter, but this does not fall directly into them. Instead, it forms a doughnut shaped ring around the black hole. This becomes very hot and pours out a lot of light, creating a light-propelled “wind” that sweeps much of the material that would otherwise go to make stars and be synthesized into heavy elements, into intergalactic space, cutting short the buildup of material required for earth-like planets.

Looking through all of this, one is struck by the number of “anomalies” that converge to provide a home for beings such as ourselves in a universe that is largely unfavorable for life. Surely, this is no coincidence, but evidence of the existence of a designing God.

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