Scientific research suggests that close flybys of asteroids or cometary bodies larger than 100 kilometres (60 mi) across could be used to move a planet in its orbit, or increase the speed of rotation. The energy required to do this is large. In his book on terraforming, one of the concepts Fogg discusses is to increase the spin of Venus using three quadrillion objects circulating between Venus and the Sun every 2 hours, each traveling at 10% of the speed of light.