I don't know - I think that at some level our discovery of Mars could be dis-proven if you think that Mars is a solid terrestrial planet then in all likelihood you are correct, but you may be wrong - Mars could be gaseous with a floating mantel and some very strange properties... That all said I'm happy to tell bible thumpers that evolution has been proven since they aren't approaching the question from a legitimate point of skepticism and trying their best to misinform others.

For everyone who is earnest though - discoveries (even the earth being round) are only accepted until they're disproven, and there have been widely accepted theories that have been disproven in the past - like how relativity blew holes in Newtonian understandings.