The Universe 05

The Solar System

Most stars belong to systems of two or three or many suns bound together by gravity. Each system is isolated from its neighbors by the light years. We are approaching a single, ordinary, yellow dwarf star surrounded by a system of nine planets, dozens of moons, thousands of asteroids, and billions of comets: the family of the sun. Only four light hours from Earth is the planet Neptune and its giant satellite, Triton. Even in the outskirts of our own solar system, we humans have barely begun our explorations. Only a century ago, we were ignorant even of the existence of the planet Pluto. Its moon, Charon, remained undiscovered until 1978. The rings of Uranus were first detected in 1977. There are new worlds to chart even this close to home. Saturn is a giant gas world. If it has a solid surface, it must lie far below the clouds we see. Saturn’s majestic rings are made of trillions of orbiting snowballs. We are now only 80 light minutes from home. A mere one and a half billion kilometers. The largest planet in our solar system is Jupiter. On its dark side, super bolts of lightning illuminate the clouds as first revealed by the Voyager spacecraft in 1979.

Inside the orbit of Jupiter are countless shattered and broken worldlets: the asteroids. These reefs and shoals mark the border of the realm of giant planets. We are now entering the shallows of the solar system. Here there are worlds with thin atmospheres and solid surfaces: Earth-like planets with landscapes crying out for careful exploration. This world is Mars. In 1976, after a year’s voyage, two robot explorers from Earth landed on this alien shore. On Mars, there is a volcano as wide as Arizona and almost three times the height of Mount Everest. We’ve named it Mount Olympus. This is a world of wonders. Mars is a planet with ancient river valleys and violent sandstorms driven by winds at half the speed of sound. There is a giant rift in its surface 5,000 kilometers long. It’s called Vallis Marineris: the valley of the Mariner spacecraft that came to explore Mars from a nearby world.

In this, our first cosmic voyage, we have just begun the reconnaissance of Mars and all those other planets and stars and galaxies. In voyages to come, we will explore them more fully. But now, we travel the few remaining light minutes to a blue and cloudy world, third from the sun. The end of our long journey is the world where we began. Our travels allow us to see the Earth anew as if we came from somewhere else. There are a hundred billion galaxies and a billion trillion stars. Why should this modest planet be the only inhabited world? To me, it seems far more likely that the cosmos is brimming over with life and intelligence. But so far, every living thing, every conscious being, every civilization we know anything about lived there, on Earth. Beneath these clouds the drama of the human species has been unfolded. We have, at last, come home.

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