"There is evidence that the solar system started out with 12 planets of which only six remain today," said maverick astronomer Tom Van Flandern when he appeared on Monday's show. Van Flandern was speaking about his Exploded Planet hypothesis, which suggests that the asteroid belt between Mars and Jupiter was once one of those 12 planets. Three of our current planets, he went on to say, were once moons (Mercury orbited Venus, Mars circled the Exploded Planet, and Pluto belonged to Neptune).
Van Flandern also delved into photographic evidence for artificial structures on Mars (images here). He said of NASA's 100,000 high resolution images sent by the Global Surveyor, 100-200 of them "turned up astonishing anomalies." Among these, were images he called "glass tubes" which could show some type of interlinking transportation network.
He also commented on the possibilities of traveling through outer space. "We have found evidence that gravity travels faster than light," Van Flandern said, intimating that one day it may be possible to build crafts that take advantage of this force.