WHY DID ASTRONOMERS THINK THERE MIGHT BE LIFE ON MARS

WHY DID ASTRONOMERS THINK THERE MIGHT BE LIFE ON MARS?

As you know,scientists are now conducting all kinds of experiments to see if life can be found anywhere else in the universe.Naturally,it is easier to explore our own solar system for signs of life than it is to probe outer space.And one of the places where some scientists thought a form of life might have been found is the planet Mars.
Why did they pick Mars? Well, Mars is considered to be a sort of twin of our own planet earth. It is the next planet beyond the earth in distance from the sun.Mars is about half the diameter of the earth and it rotates arount the in just under two years.But Mars has a day that is almost equal in lenght to our day here on earth.
In observing Mars,astronomers have noticed certain things that indicate a form of life may be possible there.First of all,Mars seasons like the earth,In face,as the seasons change on Mars,there seem to be changes on its surface.The dark areas get stronger in the spring and summer,and the colour changes from bluish-green to yellow.Could this be vegetation?
Astronomers also believe that there is at least a small amount of water vapor in the atmosphere of Mars,and this would be helpful in supporting life.Then,too,in 1887 an Italian astronomer,Giovanni Schiaparelli,reported seeing marking on the surface of Mars that resembled canals."Could these have been built by Martians in order to carry water from the polar regions to desert areas?" scientists wondered.
In 1976 two American Viking space probes landed on the surface of Mars.The instuments in the space probes searche the surrounding soil for signs of life and radioed their results back to earth.These reults showes that either there are germs in the soil or that the soil is very unusual and not like that on earth.If life does exist on Mars it would be a very simple form of life.