Early next week — assuming the weather holds — a lone man will be drifting across the Pacific Ocean for days on end, floating slowly and deliberately from the eastern edge of China all the way to Hawaii. It's a journey that will take him across the most featureless, unforgiving expanse of saltwater on Earth.

This is no sailboat, though: he'll be 5 miles above the planet in a freezing, cramped capsule, without enough oxygen to even stay conscious.

Solar Impulse 2 is one of the most ambitious aircraft ever built, because it's powered by sunlight alone; there's not a drop of gasoline spinning its four propeller engines. It's a sprawling mass of carbon fiber and silicon with a wingspan 11 and a half feet longer than a Boeing 747-8 jumbo jet. It is legitimately enormous, projecting the unwieldy awkwardness of a growth-spurting teenager whose limbs aren't quite the right size for their body. (It also looks a bit like a UFO when it's airborne.) Accomplished endurance pilots André Borschberg and Bertrand Piccard are currently flying it around the world in 12 segments in a bid to raise global awareness about renewable energy.