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à=Ð/Ð8Is There Life Out There?
Feature Article
In 1996 the world was stunned by news that scientists had discovered evidence of life having existed at one time upon Mars. The evidence came in the form of a small meteorite discovered in Antarctica which has been identified as having come from Mars. Knocked off the Martian surface millions of years ago by an asteroid impact, it drifted through space until pulled into Earth’s gravity about 30,000 years ago. Landing on Antarctica, it was gradually moved to the edge of the ice sheet by the conveyor belt action of glaciers until discovered in 1984.
Analysis of minerals and isotopes in the meteorite identify it as having originated on Mars. Recent electron microscope photographs of its interior and other experiments yield tantalizing clues that microscopic organisms once lived on Mars and their fossil remains have been preserved inside this rock. The accompanying photo is an electron microscope section of part of the interior. The fossils are clearly visible.
Of course, many other scientists dispute these findings and further research needs to be done, but it certainly brings up intriguing questions: Are we alone in the universe? Are there other civilizations capable of communicating with us? If so, why haven’t we heard from them yet? If Mars did have microscopic life, it could only have been during its early days several billion years ago when it was warmer and wetter. The chances are low that life exists on Mars now; its atmosphere is too thin and the climate too cold to sustain life as we know it. But if life did occur there, then two out of nine planets in our solar system have had life. This makes the odd favorable for life-bearing planets elsewhere.
What are the chances of life-bearing planets in other star systems? If we examine the probabilities, there are about 400 billion stars in our galaxy. Many of these are old, metal-poor stars in globular clusters and in the galactic core. That leaves some 200 billion stars in the spiral arms, which contain more metals and could therefore have planets capable of sustaining life. Of these, roughly half are binary or trinary systems. Planets in such a system would be less likely because of the gravitational tug-of-war being the stars. Any such planets would have unstable and extreme temperatures and would therefore not be very hospitable to life.
Of the 100 billion stars remaining, probably half of those actually have planets and about one-fourth of the planets are in a temperate enough zone where liquid water could exist (based on our solar system). Recent announcements of planets in such systems as 70 Andromeda and Barnard’s Star support these numbers - the planets discovered are more massive than Jupiter and usually lie further away from their star than Mars and would be too cold. This doesn’t mean, however, that smaller planets don’t exist in these systems closer to their stars.
Of the 12 billion planets remaining, most of these have probably never experienced life (although if Mars did have life, the odds increase). It took over a billion years for life to start on Earth, and 2 billion more years before life had developed into multi-celled organisms. All complex life on Earth is comparatively young, only since the Cambrian Period 600 million years ago. Intelligent life has only existed on Earth for about 3 million years or so, or about 1/1000 of the time life has been here. Our technological civilization has only been capable of sending and receiving signals from space for about 50 years out of that 3 million, or about 0.0000017 % of the time life has been here.
Working through the math, we are left with about 200 civilizations in our galaxy capable of sending signals. When you realize that the galaxy is over 100,000 light years in diameter, it is no wonder no one has answered us yet. They simply haven’t had enough time to hear us. If we continue the SETI program to send signals and listen for answers we will eventually receive a response. According to the odds, there are others out there similar to us, probably wondering if they have company in the universe. Of course, carrying on a conversation at the speed of light would be a slow process, but infinitely worthwhile.
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