In the past year or so, three internet mysteries popped up that really got my attention. They may seem very different, but trust me, they're connected. The first one is about a girl who found a door ...

This flight marked the beginning of almost a decade of research that explored the altitudes and hypersonic speed at the edge of space. At maximum speed, the X-15 would fly at Mach 6.7 ― 4,520 ...