Lesson 43 Are there strangers in space?First listen and then answer the following question.What does the 'uniquely rational way' for us to communicate with other intelligent beings in space depend on?We must conclude from the work of those who have studied the origin of life, that given a planet only approximately like our own,life is almost certain to start.Of all the planets in our solar system, we are now pretty certain the Earth is the only one on which life can survive.Mars is too dry and poor in oxygen, Venus far too hot, and so is Mercury,and the outer planets have temperatures near absolute zero and hydrogen-dominated atmospheres.But other suns, starts as the astronomers call them, are bound to have planets like our own,and as the number of stars in the universe is so vast, this possibility becomes virtual certainty.There are one hundred thousand million starts in our own Milky Way alone,and then there are three thousand million other milky ways or galaxies, in the universe.so the number of stars that we know exist is now estimated at about 300 million million million.
