Imagine a planet like the Earth, orbiting a distant star. Could that planet have life? Well, life on Earth (the only life we know) needs liquid water. So to find life on another planet, we think that that planet would have to be "just right."
The hot springs of Yellowstone National Park may be extreme environments, but they are host to a diversity of microbes that could shed light on the evolution of life on Earth and, perhaps, what lurks on distant planets.