The hunt for signs of extraterrestrial life on Mars has been one of NASA’s biggest efforts in the past few decades, leading to the Mars Sample Return mission, which allows scientists to probe Mars samples for life in depth. However, the current theory suggests that scientists discovered life on Mars 50 years ago, but NASA killed it.

To fully understand this theory, we must go back to the mid-1970s, when NASA sent two Viking land vehicles to the Red Planet. At the time, the two landers were quite successful, even performing the first and only experiment to detect life on another planet.

Back then, the results of these tests might have been clearer. As Big Think points out, some of the initial testing showed positive results. However, the gas exchange experiment did not yield positive results. Additionally, the instrument on the Viking landers, designed to detect organic compounds, detected nothing but traces of chlorinated organics.

While this was exciting, scientists at the time assumed that chlorinated organics must have been contaminated by the Earth, since there were no organic bodies. Other experiments showed the addition of water to the soil, which undoubtedly destroyed traces, leading some to believe that NASA destroyed the first evidence of life on Mars.

We are now certain that local organic compounds exist on Mars, meaning that the traces found in the 1970s are most likely not pollution from Earth. Of course, there’s no real way to prove they came from Mars. But with a more comprehensive picture of everything we’ve learned about the Red Planet over the past 50 years, it certainly looks like it could be.