When NASA announced recently that Mars once harbored the conditions necessary for life to exist, those of us who live in the Yucatan — especially the Maya — let out a collective groan. We fear another crackpot invasion. Ever since Erich Von Daniken published his best-selling “The Chariots of the Gods” in 1968, many misguided people around the world believe the Maya are the descendants of ancient space travelers. And so they flock here, usually to poke around Mayan ruins looking for telltale signs of alien visitation.