Every single American bank note is printed at Bureau of Engraving and Printing facilities, with ink and on paper each made, separately, in only one factory in the world. And yet at any given time, there is at least $70 million worth of fake U.S. currency floating around, 75 percent of which is in $100 bills. In large part because of the advent of inexpensive scanners and printers, more and more fake bills are entering circulation: From 1997 to 2007, the amount of passed counterfeit bills nearly doubled, to $64.9 million.

NASA hopes to someday use a robot like Bill Stone's DepthX to explore Europa, a frozen moon of Jupiter and one of the most probably places in our solar system to support life.