NASA’s Curiosity rover touched down on the red planet, tasked with one major goal: to assess the habitability of Mars.
The rover landed in Gale Crater in 2012. The 96-mile-wide (154 km) crater was once the site of an ancient lake. Curiosity has returned evidence that not was this once a freshwater oasis, but it could have contained microbial life.
The roaming science lab has shown that dried up mud in the region contains organic molecules. Now this doesn’t mean that Curiosity found life. But it does mean that these molecules could have a biological origin. Or maybe not.
The mud samples were collected by the rover back in 2018 and scientists have been busy analyzing them. Scientists at Washington State University believe they have identified a group of interesting molecules, called thiophenes.
Thiophenes are particularly interesting because while they form through physical processes unrelated to living organisms, their ingredients could in fact have a biological origin. The molecules are composed of hydrocarbons and sulfur; when temperatures are greater than 248 °Fahrenheit (120 °C), they react through a process called thermochemical sulphate reduction (TSR).
On Earth thiopenes are found in incredibly interesting areas: crude oil deposits (which are made from dead organisms) and in coal (made from compressed, dead plants).
So how do they form on Mars? This is the question researchers have tried to answer.
“We identified several biological pathways for thiophenes that seem more likely than chemical ones, but we still need proof,” said astrobiologist Dirk Schulze-Makuch of Washington State University.
It’s entirely possible that sometime in Mars’ past, when the planet was warmer and wetter, that bacteria and other life forms could have thrived in its surface. They may have even left their mark in the mud. As such, it’s easy to assume these molecules are biological but we can’t just assume. We need hard evidence.
According to Schulze-Makuch, the presence of thiophenes has a number of explanations, not all of which are biological. For instance, the thiophenes could have been delivered by meteorites bombarding the planet, or they could form from geological processes like volcanism. Mars is seismically active and hosts a number of volcanoes, so this could be a likely explanation.
Here’s where the next-generation Mars rovers come into play. Both NASA and the European Space Agency are sending rovers to Mars this summer, in search of life. These two rovers are equipped with specialized instruments (that Curiosity lacks) that will be able to better analyze samples on the Martian surface.
But Schulze-Makuch thinks it will take sending people to Mars before we will find any definitive proof of 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,” he said.