If all trees were blue, and every tree you had ever seen was blue, would you ask “Why are trees blue?”Maybe not. But if suddenly one day you saw a green tree, wouldn’t you ask, “Why is this tree green, when all the others are blue?”That’s what happens when you discover new things. It makes you curious. It makes you want to know why one thing is this way, and another thing is that way.That’s what exploring the solar system has done for humans. Before NASA’s two Voyager spacecraft explored them in the 1970s and 80s, we didn’t know very much about Jupiter, Saturn, Uranus, and Neptune.The Voyagers revealed surprising differences among even Jupiter’s four largest moons.Io had active volcanoes. Europa was covered in ice with crazy, criss-crossing cracks.Saturn’s rings had “spokes,” and in Saturn’s atmosphere, the wind was blowing at over 1,000 miles per hour.Neptune’s moon Triton had ice volcanoes. What a bunch of weird places!Many other NASA spacecraft have orbited or flown past these and other planets, moons, comets, and asteroids in our solar system.All in all, we have learned that our solar system is stranger and more diverse than anyone imagined.No two planets or moons look alike. Why not? Many appear to have formed in different ways.Why? And why do they orbit and rotate as they do — and where they do?Now our telescopes on Earth and in space are finding other planetary systems in our galaxy.But they have not yet found any similar to ours.Most of the gas giant planets in other solar systems orbit very close to their stars — even closer than Earth’s orbit of the Sun. Our own gas giants are way, way out there, far from our star. Why?NASA’s planetary science missions are all about figuring out our own solar system.How did it form? Why is it the way it is? Is it likely other solar systems are like ours? Just how lucky are we, anyway?Explore the solar system for yourself at The Space Place, http://spaceplace.nasa.gov/menu/solar-system.This article was written by Diane K Fisher and provided through the courtesy of the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.