earth
Planet Earth: the only home we have Of all the beautiful images humans and robotic spacecraft have captured while exploring our Solar System, perhaps none are more powerful than pictures of Earth. It can be profound and humbling to see our planet from deep space, as Planetary Society co-founder Carl Sagan eloquently explained in his 1994 book “Pale Blue Dot.” Astronauts who travel to space experience what is known as the “overview effect” upon seeing Earth from afar. They often return home feeling a deep responsibility to preserve and cherish our planet. We know of no other habitable worlds like Earth, nor do we currently have the technology to terraform a world like Mars to make it Earth-like. Earth is the fifth-largest planet in our Solar System and the third planet from the Sun. It sits in our Sun’s habitable zone , the not-too-hot, not-too-cold region around a star where liquid water can exist on a planet’s surface. Our planet’s churning liq...