Washington, D.C., is full of conspiracy theories and political intrigue at the best of times. When it comes to talk about aliens in the U.S. capital, it's often about calls for the CIA to reveal what it did with a UFO that allegedly crashed in Roswell, New Mexico, in the 1950s, or buzz about frozen alien bodies in the basement of the Pentagon. But next week in Washington, talk about aliens will be taken with furrowed-brow seriousness. It's not speculation about pregnant women and Martian abductions, but the painstaking search for possible Martian microbes. Not alien invaders, but talk about...