His business card reads: “John D. Rummel, Ph.D., Planetary Protection Officer.” He’s a cheerful, 49-year-old NASA biologist whose job is to keep the Earth safe from any microbes that might one day turn up on Mars, and to keep our own germs from contaminating the Red Planet — or any other heavenly body. Even if a spacecraft were to land on a completely sterile planet, there is a danger that microbes on a robot would take hold and forever confound scientific efforts to determine if the germs were native. “We know a lot about life in Florida,” Rummel said of NASA’s primary launching site. “We don’t want to go all the way to Mars, and discover life from Florida.”