Analyzing Organic Salts in the Lab

Decades ago, scientists predicted that organic compounds on Mars could be breaking down into salts. These salts, they argued, would be more likely to persist on the Martian surface than big, complex molecules, such as the ones that are associated with the functioning of living things.

If there were organic salts present in Martian samples, Lewis and his team wanted to find out how getting heated in the SAM oven could affect what types of gases they would release. SAM works by heating samples to upwards of 1,800 degrees Fahrenheit (1,000 degrees Celsius). The heat breaks apart molecules, releasing some of them as gases. Different molecules release different gases at specific temperatures; thus, by looking at which temperatures release which gases, scientists can infer what the sample is made of.

First Photograph Taken On Mars Surface: This is the first photograph ever taken on the surface of the planet Mars. It was obtained by Viking 1 just minutes after the spacecraft landed successfully early today [July 20, 1976]. Credit: NASA/JPL

“When heating Martian samples, there are many interactions that can happen between minerals and organic matter that could make it more difficult to draw conclusions from our experiments, so the work we’re doing is trying to pick apart those interactions so that scientists doing analyses on Mars can use this information,” Lewis said.
Lewis analyzed a range of organic salts mixed with an inert silica powder to replicate a Martian rock. He also investigated the impact of adding perchlorates to the silica mixtures. Perchlorates are salts containing chlorine and oxygen, and they are common on Mars. Scientists have long worried that they could interfere with experiments seeking signs of organic matter.

Indeed, researchers found that perchlorates did interfere with their experiments, and they pinpointed how. But they also found that the results they collected from perchlorate-containing samples better matched SAM data than when perchlorates were absent, bolstering the likelihood that organic salts are present on Mars.

Additionally, Lewis and his team reported that organic salts could be detected by Curiosity’s instrument CheMin. To determine the composition of a sample, CheMin shoots X-rays at it and measures the angle at which the X-rays are diffracted toward the detector.

Curiosity’s SAM and CheMin teams will continue to search for signals of organic salts as the rover moves into a new region on Mount Sharp in Gale Crater.

Soon, scientists will also have an opportunity to study better-preserved soil below the Martian surface. The European Space Agency’s forthcoming ExoMars rover, which is equipped to drill down to 6.5 feet, or 2 meters, will carry a Goddard instrument that will analyze the chemistry of these deeper Martian layers. NASA’s Perseverance rover doesn’t have an instrument that can detect organic salts, but the rover is collecting samples for future return to Earth, where scientists can use sophisticated lab machines to look for organic compounds.