At 35,000 km the circumference of the world is a long way to travel. Embarking today, an experimental aeroplane, Solar Impulse-2, is going to make that journey by solar power alone. I'm very excited about this, partly because planes are cool, but mostly as it's a giant leap forward for green technology.
The aeroplane is wider than a jumbo jet but less than 1% of the weight. However it can only hold one pilot and travels no faster than a car. But I've no doubt it's the shape of things to come.