One of humanity's greatest mysteries might have been solved 50 years ago - but NASA might have destroyed all evidence of it.
Since its formation, the space agency has performed a series of projects to chart the landscape of Mars and to search for evidence to prove the existence of extraterrestrial life on the Red Planet.
One scientist believes that NASA may have already found such evidence, but that bungling scientists might have accidentally "destroyed" it.
Dirk Schulze-Makuch, president of the German Society for Astrobiology, wrote an article for Big Think in which he made the "provocative" suggestion.
"That we already found life on Mars almost 50 years ago but that without realising it, we killed it," the article reads.
The investigation he would have been referring to was the Viking lander, which touched down on the surface in the mid-1970s.
Both landers were capable of detecting life, but they beamed back results that NASA branded "confusing".
One of the tests showed a negative for gas exchange, making life unlikely, and another instrument capable of detecting organic compounds picked some up, but they were interpreted as "pollution from Earth".
Viking project scientist Gerald Soffen then said, "Without bodies, there is no life”, meaning that without organic compounds there couldn't be alien life.
The Viking mission then concluded that there was no presence of Martian life, or at best it was an inconclusive mission.
It wasn't until 2008 when the Phoenix lander touched down, sending off its Curiositt and Perseverance rovers to explore the planet, that NASA found native organic compounds.
Schulze-Makuch says that the methods used to determine signs of life during the Viking missions could have in fact destroyed the very alien life they were trying to find.
One example of the methods was applying water to soil samples, which could have killed organisms and "may explain the puzzling results".
He added: "It seemed reasonable that adding water [at the time] could encourage life to show itself in the extremely dry Martian environment."
“In hindsight, the approach may have been too good. What other researchers and I have learned in extremely dry places on Earth, such as the Atacama desert in Chile, is that there is a gradual progression of life forms as the habitat becomes more arid," added Schulze-Makuch.
"Perhaps the putative Martian microbes collected for the labeled release experiments couldn't deal with that much water and died after a while," he added.
