In 1976, in a life detection experiment, based on the data returned by the two Viking landers, researchers were surprised to find four positive results. They detected “microbial respiration”. The test curves from Mars were the same as those on Earth’s soil. The curves produced by the tests were similar, but since no organic matter was found in the sample, NASA believed it was only life-like material. Since then, NASA has not installed life-detection equipment on the lander to follow up on this discovery.