Who's to say that Mars, Venus, or even the Earth aren't already migrating into slightly different orbits?
How reliably can we measure the distance between worlds? If earth's orbit were expanding, I assume we could measure our a year getting longer, but how long have we actually been able to do that reliably, and even still, how accurate are such measurments.
By the way, I propose that we are now in Year 1 of the new age.