This story is part of, our series exploring the red planet.
Before we get into this, let's make it clear we haven't yet found life on Mars.
Scientists are investigating Martian thiophenes, organic molecules that are found in white truffles and coal on our planet. The question is if those compounds formed through chemical or biological processes on Mars. Researchers aren't ruling out a biological origin.
Astrobiologists with Washington State University (WSU) and Technische Universität in Berlin published a paper in February in the journal Astrobiology that discusses the possible origin of the thiophenes discovered by NASA's Curiosity Rover.
In 2018, NASA announced the rover had "found new evidence preserved in rocks on Mars that suggests the planet could have supported ancient life." That evidence involved a list of organic molecules, including thiophenes.
"If you find thiophenes on Earth, then you would think they are biological, but on Mars, of course, the bar to prove that has to be quite a bit higher," said Technische Universität's Dirk Schulze-Makuch, co-author of the paper, in a WSU release on Thursday.
There are both biological and chemical explanations for the thiophenes and we don't know for certain which process created the molecules on Mars. A biological origin would have involved bacteria billions of years ago.
A new batch of rovers (and ) heading to the red planet may be able to shine more light on this mystery in the coming years.
In the meantime, the astrobiologists are leaving the thiophenes as an open question. Add it to the pile of queries we still have about Mars, including where that.
How will we know for certain if Mars hosts life? "I think the proof will really require that we actually send people there, and an astronaut looks through a microscope and sees a moving microbe," Schulze-Makuch said.