Cradle of Life As We Know It
Earth is the only place we know of in the universe that harbors life. Ours is the largest terrestrial planet in the solar system. Our rocky, volcanic world is coated in a thin veneer of liquid water, living things, and translucent atmosphere, whose complicated interactions make Earth's surface into a place of constant change. We humans have only had fifty years of perspective on Earth as a planet, of seeing it as a "pale blue dot" floating in the black vacuum of space.
With that perspective, we know precious and unique our planet is. We know, too, that we are having measurable effects on the complex interactions of ocean, land, life, water, and air, changing our climate. But predicting the future of our climate is hard. Understanding how Earth's systems work by studying the way they operate on other worlds is a major goal of planetary exploration. Mars, Venus, and Titan all have (or had) active geology, hydrology, and weather -- but, as far as we know, they don't have life. Is Earth really that unique? Are we truly alone in the universe? We won't know unless we keep searching.
News from Earth
The Chang'e 5 test vehicle's short mission is more than half over. It has rounded the far side of the Moon and is on its way back to Earth for a planned October 31 test of lunar sample return technology. It's not a science mission -- it's an engineering mission -- but it has managed to return an absolutely iconic photo of its distant home, seen across the very unfamiliar far side of the Moon.
Watch as our enormous moon -- a quarter the diameter of the planet -- just winks out as it passes into Earth's long shadow, in an animation captured from more than 100 million kilometers away.
Earth's Place in Space
In 2016, The Planetary Society’s LightSail program will take the technology a step further.