[John Paul]

John Paul asked the Naked Scientists:
   
What evidence has lead scientists to conclude that the earth is one member of a solar system consisting of other planets?

What do you think?

[damocles]

Umm...

Initially I suppose the evidence comes from the observed behaviour and motions of the other planets in the sky: both the positions and the observed phases (Mercury and Venus seen a crescent through full disk, but smaller as they get fuller; outer planets only ever seen in a variety of gibbous phases)

But the strongest evidence surely comes in the fact that both American and Soviet teams were able to successfully target and deliver payloads to other planets along complicated trajectories that were calculated according to this assumption. Space is so vast and empty there is no chance that they could have arrived at a target planet if the underlying assumptions at this very basic level were wrong.