Date: 25 January 2002
Subject: Physics/Cosmology

Are there many inhabited planets throughout the universe, and is this a problem for theology?

The last few months have seen some major new breakthroughs in the search for other inhabitable planets. The basic difficulty with looking for planets, as against stars, is that they are small and shine only by reflected light. Those in our own solar system are, of course, very close to us in astronomical terms. The outer planet Neptune orbits about thirty times as far out as we are. Light travels at around 300,000 kilometers or 176.000 miles per second across space, and takes around nine minutes to reach us from our Sun. The light from Neptune would therefore take less than 5 hours to reach us even at its furthest point. The light from the nearest star takes around two years to reach us. If it has a system of planets we are unlikely to be able to detect them by any reflected light. Even in the nineteenth century, however, the planet Neptune was first located because of its gravitational effect on Uranus. Planets have small effects even on the stars they orbit ? and increasing sophistication in equipment has enabled us to detect this. In 1995 a planet half the size of Jupiter was detected orbiting the star 51 Pegasi. In six years astronomers have detected 66 systems with 74 planets in them.

Are they inhabitable? Life as we know it can actually survive in some fairly extreme earth conditions. Our earth, however, is temperate compared e.g. to its sister planet Venus, which has a very hot dense atmosphere of CO2, with swirling clouds of sulfuric acid. We need the heavy outer planets like Jupiter, too, to sweep up incoming asteroids before they hit us and exterminate life. Inhabitable planets need a fairly precisely specified system.

Most of the planets discovered so far turn out to be so close to their stars that they would be impossibly hot. Last August, though, Debra Fischer (a colleague of veteran planet hunter Geoff Marcy) discovered the second of two planets orbiting 47 Ursae Majoris, which seem to have orbits fairly like ours around a sun also fairly like ours.

Astronomers differ still over details of the dynamics of planetary formation and life cycles, but perhaps 5-10% of them may turn out to have planets something like ours. Given the vastness of the universe, this would imply many other Earths.

Is this threatening to theology? Might there be other intelligent life forms out there? It may be a surprise to many to know that the overwhelmingly common traditional view of the church has tended to be that there are likely to be ?other worlds? and other intelligent inhabitants for them.

So much so, that when the fairly orthodox William Whewell wrote a book on the Plurality of Worlds he was nervous to suggest that we might be the only intelligent life ? and was attacked by the outraged evangelical David Brewster in a book More Worlds Than One in 1854 who insisted that God surely had made others.

Whatever side we personally come down on in this debate, the Bible only tells us that God is very interested in us ? not necessarily that we are his only interest. Christians, of course, have nothing to fear from ?War of the Worlds? type invasions of aliens if God is indeed sovereign of the whole universe. In any case, the distances away any inhabitable or inhabited planets are likely to be, are so vast, that we needn?t hold our breath waiting for visitors.