Are We Alone?: Humankind's Search for Extraterrestrial Civilizations

In December 2014 scientists announced that NASA's Curiosity rover had detected spikes of methane in the atmosphere of Mars and evidence of carbon-based organic molecules in Martian rock samples. Oceans covered much of Mars in the ancient past, and seasonal dark streaks observed on the Red Planet's surface today may be caused by salty flowing water. Oceanic icy worlds have also been found in Jovian moons, Europa, Callisto, and Ganymede; in Saturn's moons, Enceladus and Titan; and probably in Neptune's moon, Triton. Since life as we know it needs water, these revelations are some of the latest in a growing body of evidence leading ever closer to the answer to humanity's greatest question-does life exist beyond planet Earth? Earth revolves around one of billions of stars in the Milky Way, which is but one of billions of galaxies in the known universe. With odds like this, it seems likely that humankind is not alone. The cutting edge of science promises to provide clues to a definitive