Science - science done right - allows for rebuttals, challenges, and overturning previous conclusions. Last year, NASA made a big deal out of the report that a microorganism had turned up which still reproduced even if highly toxic arsenic were substituted for phosphorous in its makeup.
Two new papers have been published that contradict the previous findings. One says the original team's samples were contaminated, screwing up results, the other saying the creatures don;t die with arsenic "installation," but they don't reproduce, either.
Despite all this, Dr. Felisa Wolfe-Simon of NASA’s Astrobiology Institute is sticking to her guns. She's convinced that further study will show the original finding was right.
Good science can be messy. This is a good example.