Turns out that the methane that was found on Mars is not a product of meteor strikes, scientists have found, which means Mars actually produces methane.

My question is: Where are the green aliens that fart all day to produce it?

NOTE: After careful investigation, I found the following: "According to Dr. James L. A. Roth, the author of Gastrointestinal Gas (Ch. 17 in Gastroenterology, v. 4, 1976) most people (2/3 of adults) pass farts that contain no methane. If both parents are methane producers, their children have a 95% chance of being producers as well.". Go figure.