Question

What is the possibility of life other planets?

In order for life (in the form that is most familiar to us) to evolve on a planet, scientists believe that the planet must be warm enough to contain at least some liquid water, but not so hot that all of the water turns to vapor, as appears to be the case on the planet Venus. It must also contain certain important elements, like carbon and nitrogen, that are necessary to build living cells, and the environment must be calm enough that life has time to develop - the planets in some star systems may be hit so frequently by giant meteorites (causing all the surface water to boil or vaporize) that life never has a chance to form there. Earth is a very special place, in that it appears to be the perfect environment for life to form and flourish. In our own solar system, we see that Mars also had water at its surface long ago, and some very primitive life forms (like bacteria) could have developed there - scientists are still debating whether or not one of the meteorites that came from Mars, ALH84001, has fossil evidence of ancient life on Mars. One of Jupiter's moons, Europa, also might contain liquid water deep beneath its surface, which could harbor primitive life forms.

There is also a strong possibility of planets outside of our solar system having the conditions necessary for life. Our galaxy, the Milky Way, contains at least 200 billion (200,000,000,000) stars, and recent observations with very powerful telescopes suggests that many of the stars in the night sky have planets orbiting them. There is a famous equation called Drake's Equation that tries to calculate how many stars contain orbiting planets that have conditions suitable for the development of life. The equation suggests that life forms are very likely to exist on planets in our galaxy or any of the billions of other galaxies in the Universe. Scientists are still working hard to observe earth-like planets around other stars, and to understand the conditions under which life formed and evolved on the ancient Earth.

Prof. Brian W. Stewar University of Pittsburgh
January 28, 2002