Transcript: The first place to conduct the search for life beyond Earth is our own solar system. Each of the planets in the solar system is hundreds of thousands of times closer than the next nearest extrasolar planets around nearby stars. So astronomers must start by closely inspecting all the planets and the major moons of the solar system for evidence of life. We can use remote sensing techniques, spectroscopy to tell us what the chemical composition of the surface material is. We can use flybys to measure in different regions of the electromagnetic spectrum, and in some cases we can use landers. We have to remember that evolution is an issue. The solar system conditions may have changed over billions of years. The habitable zone, the region of liquid water, that now encompasses only the Earth, may once have included either Mars or Venus. We may start by ruling out some environments. Mercury is almost certainly too hot and has almost no atmosphere. It's a moon-like object and so is unlikely to have life. Pluto and small bodies in the outer solar system are also unlikely to have life because their liquid materials and even their organic materials have been frozen. Asteroids and comets have ices, and they have been liquefied at times for never more than a million years at a time which most biologists think is too short of for life to develop. So we can start by ruling out some of the more extreme environments in the solar system.