NASA's Viking landers may have destroyed organic material on Mars. Pictured, a selfie of Curiosity Mars rover compiled from many smaller images — which is why the mechanical arm holding the camera is not visible. NASA, JPL-Caltech, MSSS

Just last month, NASA announced the discovery of complex organic material on Mars, which could be related to some form of ancient microbial life. The revolutionary find is the key to better understanding the red planet but if a new report is anything to go by, the American space agency might have discovered Martian organic compounds decades ago in the 70s and then destroyed it.

Organic compounds can be related to non-biological processes, but they also make up building blocks of life as we know it. Scientists across the globe have been hunting for these materials on Mars and other worlds, and NASA has been at the forefront of this search.

Back in 1976, the agency sent two landers to the red planet as part of its Viking mission. It hoped the instruments on these machines would find traces of organic compounds, either signifying signs of ancient life or material delivered through meteorites. However, the mission did not provide any evidence, raising a number of questions and theories related to Mars.

“It was just completely unexpected and inconsistent with what we knew,” NASA planetary scientist Chris McKay told New Scientist. “You get some new insight, and you realize that everything you knew was wrong.”

The inconclusive findings led many to think meteorites crashing onto the Martian surface were not just depositing organic compounds but also destroying them. However, the theory was reconsidered when the agency’s Phoenix lander found the evidence of a compound called perchlorate in 2008.

Known for its explosive tendencies, perchlorate is widely used for making flares, explosives, blasting agents, fireworks, and military munitions such as grenades. It ignites at extremely high temperatures, which indicated any organic material likely found by Viking lander might have been destroyed when the lander’s gas chromatograph-mass spectrometer would have heated the soil to trace the molecules.

Though there was no evidence to confirm the theory, it got further support in the year 2013 when NASA’s Curiosity Mars rover found chlorobenzene on the red planet. This molecule forms due to the burning of carbon with perchlorate.

This prompted McKay, Melissa Guzman from LATMOS research center in France, and colleagues to reanalyze the data collected under the Viking mission. The joint effort revealed chlorobenzene was also detected on the Martian surface all the way back in the 70s.

While this suggests heating of perchlorate destroyed organic compounds and formed this molecule, there is no sure way to confirm this idea. As the researchers involved in the study suggest it is also possible chlorobenzene detected decades ago might be that trapped from Earth and contaminated the lander’s equipment.

NASA has been using heating techniques to find organic compounds. Curiosity did the same to locate sulfur and carbon compounds. The rock, mudstone, tested by the rover didn’t contain perchlorate, which probably helped with the detection.

The study titled, “Identification of Chlorobenzene in the Viking Gas Chromatograph ‐ Mass Spectrometer Data Sets: Reanalysis of Viking Mission Data Consistent With Aromatic Organic Compounds on Mars,” was published in the Journal of Geophysical Research: Planets.