Curiosity rover finds erased pieces of rock, revealing clues

A new article enriches scientists ‘understanding of where the rock record preserved or destroyed evidence of Mars’ past and possible signs of ancient life.

Today, Mars is a planet of extremes: it is extremely cold, has high radiation, and is dry. But billions of years ago, Mars was home to lake systems that could have supported microbial life. As the planet’s climate changed, one of these lakes, in Mars’ Gale Crater, slowly dried up. Scientists have new evidence that the brine, or brine, seeped deep through cracks, between grains of soil in the parched bottom of the lake, and weathered the mineral-rich layers below.

The results published in the July 9 edition of the journal Science and led by the team in charge of the Chemistry and Mineralogy Instrument, or CheMin, aboard NASA’s Mars Science Laboratory Curiosity rover, helps to better understand where the rock recording preserved or destroyed evidence of the past of Mars and the possible signs of ancient life.

“We thought that once these layers of clay minerals formed at the bottom of the lake in Gale Crater, they stayed that way, preserving when they formed over billions of years,” said Tom Bristow. , Principal Investigator and Head of CheMin. author of the article at NASA’s Ames Research Center in Silicon Valley, California. “But later, the brines destroyed these clay minerals in some places, essentially resetting the rock record.”

March: it’s okay on your permanent record

Mars has a treasure trove of rocks and minerals that are incredibly old compared to Earth. And with the rock layers intact at Gale Crater, scientists knew it would be a great site to search for evidence of the planet’s history, and possibly life.

Using CheMin, the scientists compared samples taken from two areas about a quarter of a mile apart from a layer of mudstone deposited billions of years ago at the bottom of Gale Crater Lake. Surprisingly, in one region, about half of the clay minerals they expected to find were missing. Instead, they found mudstones rich in iron oxides, minerals that give Mars its characteristic rusty red color.

Scientists knew that the mudstones sampled were roughly the same age and were initially the same, loaded with clay, in the two areas studied. So why, as Curiosity explored the sedimentary clay deposits along Gale Crater, have patches of clay minerals – and the evidence they preserved – “disappeared”?

Clays contain clues

Minerals are like a time capsule; they provide a record of what the environment looked like when they were formed. Clay minerals have water in their structure and are evidence that the soils and rocks that contain them have come into contact with water at some point.

“Since the minerals we find on Mars are also forming in certain places on Earth, we can use what we know about their formation on Earth to tell us how salty or acidic the waters of ancient Mars were.” said Liz Rampe, CheMin’s assistant principal researcher and co-author at NASA’s Johnson Space Center in Houston.

Previous work revealed that as long as the Gale Crater lakes were present and even after they dried up, groundwater moved below the surface, dissolving and carrying chemicals. After their deposition and burial, some pockets of mudstone experienced different conditions and processes due to interactions with these waters which altered the mineralogy. This process, called “diagenesis,” often complicates or erases the soil’s earlier history and writes a new one.

Diagenesis creates an underground environment that can support microbial life. In fact, some very unique habitats on Earth, in which microbes thrive, are known as “deep biospheres”.

“These are great places to look for evidence of ancient life and assess habitability,” said John Grotzinger, co-investigator and co-author of CheMin at the California Institute of Technology, or Caltech, in Pasadena, Calif. . “Even though diagenesis can erase the signs of life in the original lake, it creates the chemical gradients necessary to support life underground, so we’re really excited to have discovered this.”

By comparing the mineral details of the two samples, the team concluded that brackish water filtering through the overlying sediment layers was responsible for the changes. Unlike the relatively freshwater lake that was present when the mudstones formed, the salt water is believed to have originated from later lakes that existed in an overall drier environment. Scientists believe these findings provide further evidence of the impacts of climate change on Mars billions of years ago. They also provide more detailed information which is then used to guide the Curiosity rover’s investigations into the history of the Red Planet. This information will also be used by NASA’s Mars 2020 Perseverance rover team when evaluating and selecting rock samples for possible return to Earth.

“We have learned something very important: Parts of the Martian rock records are not very effective in preserving evidence of past and possible life on the planet,” said Ashwin Vasavada, scientist of the Curiosity project and co-author of the NASA jet. Propulsion laboratory in Southern California. “Luckily, we find them both close to each other in Gale Crater and we can use mineralogy to tell which is what.”

Curiosity is in the initial phase of investigating the transition to a “sulphate-containing unit,” or rocks that may have formed as Mars’ climate dried up.