In the summer of 1989, from a remote expanse of our solar system where sunlight is merely a tepid glow, NASA's Voyager 2 spacecraft radioed to Earth humankind's very first images of Neptune. The pictures revealed the sun's outermost planet was a stunning, deep blue orb. In contrast, Uranus, Neptune's planetary neighbor and the first to be discovered with a telescope, appeared noticeably paler.
Both seemingly twin worlds have a lot in common. They're roughly the same size, almost equally massive and are both enveloped with deep atmospheres made of similar materials. So why were the two orbs different shades of blue? This is a question that has puzzled scientists for decades.
