Freshly fallen meteorites, far from being red hot, often have frost on them from condensation. Any microbial passengers would have a gentle landing. If ancient Mars life also left modern descendants at home, the biohazard to its cousins on Earth is much higher than that from two independent strands of life. The same argument holds if the transfer was from Mars to Earth. NASA has implemented some protocols for its Mars samples, but the issue includes more than just that planet.
Some scientists remain unconvinced that current protections are good enough.
A new group called the International Committee Against Mars Sample Return recently launched a Web site discussing its concerns, with links to other documents on planetary quarantine. Barry DiGregorio, co-founder of the group, says he's concerned that NASA may relax its standards of Mars samples. James Oberg spent 22 years as a rocket scientist for NASA, and has written eight books and numerous articles on space flight. Life on the Moon, Maybe It's commonly thought that on at least one occasion, infectious germs were brought back from the moon. This occurred on the Apollo 12 mission in November 1969, when the crew retrieved pieces of the Surveyor 3 robot that had been on the moon for two years.