Are We All Alone In the Universe?


The Sunday Nation


16 October 2005


Many readers have often asked whether there is life in outer space. The quick answer is that nobody knows. This is question arises perhaps because humans don’t like feeling lonely, and when we look up the sky we can’t accept the though that we might be the only ones around.

Life as we know it can only exist on a planet. So we can get an answer by finding out whether planets exist outside our solar system. It is estimated that ten percent of all stars in the universe are similar to our sun. Out of these sun-like stars, only five percent have a planetary system. And only one percent of the “solar” systems can have an earth-like planet.

In summary, an earth-like planet can only exist in one percent of five percent of ten percent of all stars! That is a very small fraction. Furthermore, the fact that a planet has similar properties to the earth doesn’t mean that it will have life. Perhaps only less than one percent of the earths-likes have life. So is it worth wondering if we are all alone?

Let’s find out: our Milky Way galaxy is a typical galaxy and it has about 300 billion other stars – Yes; billion with a “b”. There are about 100 billion galaxies in the universe thus there are about 30,000 billion-billion stars in existence.

Ten percent of all stars (that is 3,000 billion-billion) are sun-like.  Five percent of the sun-like stars (150 billion-billion) have planetary systems; and one percent of the “solar” systems (1.5 billion-billion) have earth like planets. The question then is, is it reasonable to expect that out of 1.5 billion-billion earth-like planets, only one has life? That is not a question for this kind of a column!

The above numbers are just estimates, the truth is that to date only 145 planets have been seen outside the solar system. The first was detected in 1992 and only confirmed three years later in 1995.

Most of these extra-solar planets are very large – comparable to Jupiter in size. The nearest one is some 10 light-years away and the furthest is over 17,000 light years away. A light year is the distance that light would travel in one year. It is equal to about 9.5 trillion kilometres.

Out of the 145 known extra-solar planets, 6 are earth-like but not in all terms of the phrase: only one has comparable mass, three are located the same distance from their stars as the earth is from the sun; and two take about one 360 days to go round their stars. None of these earth-likes are known to have an atmosphere.

Nevertheless, these are very encouraging discoveries and they point to the conclusion that we may not be all alone after all.

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