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Salts Could Be Important Piece of Martian Organic Puzzle
A NASA team has found that organic salts are likely present on Mars. Like shards of ancient pottery, these salts are the chemical remnants of organic compounds, such as those previously detected by NASA’s Curiosity rover. Organic compounds and salts on Mars could have formed by geologic processes or be remnants of ancient microbial life.
This look back at a dune that NASA's Curiosity Mars rover drove across was taken by the rover's Mast Camera (Mastcam) on Feb. 9, 2014 – the 538th Martian day, or sol, of Curiosity's mission. Photo: NASA/JPL-Caltech/MSSS
Besides adding more evidence to the idea that there once was organic matter on Mars, directly detecting organic salts would also support modern-day Martian habitability, given that on Earth, some organisms can use organic salts, such as oxalates and acetates, for energy.
“If we determine that there are organic salts concentrated anywhere on Mars, we’ll want to investigate those regions further, and ideally drill deeper below the surface where organic matter could be better preserved,” said James M. T. Lewis, an organic geochemist who led the research.
Lewis’s lab experiments and analysis of data from the Sample Analysis at Mars (SAM), a portable chemistry lab inside Curiosity’s belly, indirectly point to the presence of organic salts.
But directly identifying them on Mars is hard to do with instruments like SAM, which heats Martian soil and rocks to release gases that reveal the composition of these samples.
The challenge is that heating organic salts produces only simple gases that could be released by other ingredients in Martian soil.
Finding organic molecules, or their organic salt remnants, is essential in NASA’s search for life on other worlds. But this is a challenging task on the surface of Mars, where billions of years of radiation have erased or broken apart organic matter.
Curiosity collects Martian soil and rocks, which may contain tiny chunks of organic compounds, and then SAM and other instruments identify their chemical structure.
Using data that Curiosity beams down to Earth, scientists like Lewis and his team try to piece together these broken organic pieces. Their goal is to infer what type of larger molecules they may once have belonged to and what those molecules could reveal about the ancient environment and potential biology on Mars.
While some experts have predicted for decades that ancient organic compounds are preserved on Mars, it took experiments by Curiosity’s SAM to confirm this.
For example, in 2018, NASA Goddard astrobiologist Jennifer L. Eigenbrode led an international team of Curiosity mission scientists who reported the detection of myriad molecules containing an essential element of life as we know it: carbon. Scientists identify most carbon-containing molecules as “organic.”
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. (NASA)
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