Post by Ruthanna Gordon
Humans have often speculated about the possibility of extraterrestrial life. As our ability to detect conditions on other worlds has improved, we have both narrowed and expanded the set of possibilities for what’s out there.
In the early years of the twentieth century, many believed that intelligences not too different from our own existed within the solar system. These hopes, and fears, have long since been laid to rest: Martian canals turn out to have been the product of an overenthusiastic imagination, and Venus harbors no dinosaurs. However, recent research suggests that relatively primitive life forms may be more abundant than we thought.
Life on earth depends on a few basic requirements. Carbon is needed as a building block for organic molecules. And liquid water is its necessary complement. Even in the most extreme conditions, terrestrial life flourishes wherever these two things can be found. And they seem to be surprisingly common elsewhere.
One way to get liquid water is to have your planet orbit in the “Goldilocks Zone”—the temperate band not so far from a star that water freezes, and not so close that it boils. But other factors can have the same effect. Molten rock or radioactivity can melt ice. The presence of salt or ammonia can prevent freezing, just as they do on a highway or in your car. We’ve found evidence for liquid water in the clouds of Venus, in the asteroid belt, and on moons orbiting Jupiter and Saturn. We may even have taken pictures of it on Mars.
The next step is a more direct search. The Curiosity Rover is scheduled to land on Mars in 2012, where it will analyze the rocks for chemicals characteristic of life.