New Worlds, New Hope for Extra Terrestrial Life

Copyright Brent Silby 2000


Astronomers are showing us that planets are a relatively common phenomenon in our galaxy. Until the mid 1990's, there was no evidence of 'exoplanets' (that's what scientists call planets that orbit stars other than our sun), and any theories regarding the existence of planets outside our solar system were mere speculation. As far as we knew, our solar system was the only one that contained planets. If this had turned out to be true, our hopes of finding extra-terrestrial life would have been virtually non-existent. The search would have ended there.

But now our technology has improved and scientists have discovered over 50 exoplanets. Interestingly, astronomers cannot actually see these planets. This is because planets are not self luminous. Usually the only way to see a planet is from reflected light, which usually originates in a nearby star. But exoplanets are so far away from Earth that their reflected light is obscured by the brightness of their parent star, which means that astronomers have to find them in other ways. One such way is to infer their existence by looking at the gravitational effect they have on their parent star. Astronomers observe stars to see if they are being pulled by something close by -- something that can't be seen. Small 'wobbles' in a star's movement betray the presence of an orbiting planet. Observations of stars in this galaxy show that such wobbles are common place. If scientists are correct in supposing that these wobbles are caused by planets, then it seems that planets are relatively common. Enough evidence exists to suggest that the galaxy is full of planets.

By analyzing the magnitude of star wobbles, astronomers have determined that most of the exoplanets discovered so far are gas giants like Jupiter. Such planets are inhospitable and are not suitable for life as we know it. But we are just at the beginning of the search. As technology improves, smaller planets may be found. One day we may be able to use spectral analysis to determine what sorts of atmosphere they have. Perhaps we will find some that have Earth-like atmospheres. This possibility staggers the imagination. As far as we know, Earth is the only planet that supports life, but if we discover other Earth-like planets, we will face the possibility that some of them might support life -- some of which might be intelligent.

The discovery of extra-terrestrial life will be the most profound discovery in human history. It will change the way we view ourselves and the way we think about our place in the universe. But the question is still open. The discovery is still waiting to be made. Will we ever discover life on other worlds? Since other star systems are so far away, we cannot hope to explore them in the foreseeable future. With our current technology, a trip to the nearest star system would take over 40,000 years. And even if we developed propulsion systems that would move us at the speed of light, we would have Einsteinian relativity problems to overcome. One of these problems is the so-called 'time dilation' effect, which suggests that time moves slower for a person who is travelling at great speed. In effect, Einstein's theory states that if I travel to a nearby star system at the speed of light, from my point of view the trip would be instantaneous, but from the point of view of my friends on Earth, I will have been gone for several years. Given such transportation difficulties, it appears that the best way to discover life in other star systems is to observe it from here.

Finding extra terrestrial life is no easy task. Since we are stuck here, on Earth, the only type of alien life we can search for is intelligent life capable of radio communication. This limits the scope of our search, but for now there is no choice. SETI (the Search for Extra Terrestrial Intelligence) is an organization that is committed to discovering intelligent life in the galaxy. They search for life by systematically scanning the sky for radio signals that do not originate on Earth. The hope is that we might be able to eavesdrop on the internal communications of another civilization. We know that the chance of picking up a signal that was deliberately sent to us is extremely low, but we also know that intelligent civilizations probably use radio for their own communications. This is what SETI is trying to find. SETI have organized a system by which millions of personal computers around the world work on small chunks of radio data that has been picked up by radio telescopes. These computers sort through random background noise, and search for patterns that have no astronomical origin -- patterns that might have an intelligent origin. With any luck, SETI will find a star system that contains a planet, which is inhabited by intelligent life that has attained the capability to communicate through radio. If this happens we can decide whether we should attempt to communicate directly with the civilization -- a pretty big decision -- or leave it alone.

The continuing discovery of exoplanets gives us hope. We now know that the nine planets orbiting our sun are not alone in the universe. Knowing that there are planets elsewhere in our galaxy gives us good reason to suppose that extra terrestrial life exists somewhere in the cosmos. After all, if life can arise on Earth, then life can arise on other suitable worlds. This thought reaffirms the wisdom of searching for alien civilizations and gives the human species a goal to work towards.

Copyright Brent Silby 2000
Department of Philosophy
University of Canterbury
New Zealand