I don't need to go to Mars to know its real. All I have to do is look up in the sky in someplace where there isn't a lot of light pollution. The theory of evolution is still a theory, but I accept it because it is the most logical explanation. Scientific discovery is based on empirical evidence, that has been confirmed time and time again. Historical fact is often warped and re shaped, depending on who's stating. An example of this is the Armenian genocide. One side calls it genocide because the Turks killed about 1.5 million Armenians, and the other side denies that it was genocide and merely an action of retaliation against the Armenians, and that they didn't kill that many. History is debated and debated, but scientific discoveries can be confirmed again and again because evidence can be renewed and rediscovered. If all you have are the mentionings and writings of long deceased figures, then how can you know how credible they actually are. Historical fact is defined by record keeping. Record keeping is vulnerable to human flaws and errors as well as exaggeration. It is only until hard, concrete evidence, which can deteriorate over time, is discovered.