Mars is perceived as a red planet, with all its images seen by the world so far showing red rocks and craters. When NASA’s Perseverance rover landed in the Jezero Crater on Mars, scientists too hadn’t expected anything different to see. But what the rover found on the ground was surprising.
The Jezero Crater was chosen as the spot for the rover to land because of its history as a lake and part of a “rich river system, back when Mars had liquid water, air and a magnetic field”.
Analysing data from the rover, planetary scientists Roger Wiens and Briony Horgan, professor and associate professor, respectively, of earth, atmospheric, and planetary sciences at Purdue’s College of Science, made some startling discoveries, which were recently published in journals Science and Science Advances.
While the rover was expected to see sedimentary rocks “washed in by rivers and accumulated on the lake bottom”, it found many of these rocks volcanic in nature, according to a statement issued by Purdue University, which added that these rocks were found to be composed of “large grains of olivine, the muddier less-gemlike version of peridot that tints so many of Hawaii’s beaches dark green”.
“We started to realize that these layered igneous rocks we were seeing look different from the igneous rocks we have these days on Earth. They’re very like igneous rocks on Earth early in its existence,” Wiens was quoted as saying.
It was Wiens who led the design and construction of the SuperCam on Perseverance that helps analyse samples and determine the type and origin of the rocks. Horgan, meanwhile, helped select Jezero Crater as the landing site for the rover.
According to the scientists, the rocks and lava being examined by the rover on Mars are nearly 4 billion years old. It’s not that such old rocks have not been found on Earth, but they are incredibly weather-beaten due to our planet’s active tectonic plates besides the weathering effects of wind, water and life over billions of years. On Mars, however, these rocks are pristine and hence much easier to study, the university said.
The Jezero Crater Surprise
NASA’s Perseverance rover began examining rocks on the floor of Jezero Crater on Mars in the spring of 2021. Scientists were in for a surprise when rover shared what they found. Since there was a lake at the site billions of years ago, the expection was to find sedimentary rock that would have formed after sand and mud settled in the watery environment. What the rover discovered, instead, was that the floor was made two kinds of igneous rock — one that formed from magma deep underground, and the other from volcanic activity on the surface, NASA said.
Igneous rocks are considered to be great timekeepers as the crystals in them record a lot of details about the exact moment they were formed.
Ken Farley of Caltech, Perseverance’s project scientist and the lead author of a Science paper mentioned above, said in a NASA blog: “One great value of the igneous rocks we collected is that they will tell us about when the lake was present in Jezero. We know it was there more recently than the igneous crater floor rocks formed.” He said this would address some major questions like when was Mars’ climate conducive to lakes and rivers, and when it changed to the very cold and dry conditions seen at present.
One of Perseverance’s main stated goals is the search for life. However, according to NASA, igneous rock because of the way it is formed isn’t ideal for preservation of the potential signs of ancient microscopic life that the rover is searching for. Sedimentary rock, on the other hand, often forms in watery environments that are suitable for life and is hence better at preserving ancient signs of life. However, it is difficult to determine the age of sedimentary rock, particularly when it contains fragments formed at different times before the sediment was deposited.
This is why scientists had found the sediment-rich river delta the rover has been exploring since April 2022 so “tantalizing”, NASA said.
“From orbit, we looked at these rocks and said, ‘Oh, they have beautiful layers!’ So we thought they were sedimentary rocks. And it wasn’t until we were very close up and looked at them, at the millimeter scale, that we understood that these are not sedimentary rocks. They’re actually ancient lava. It was a huge moment when we figured that out on the ground, and it really illustrated why we need this kind of exploration,” Horgan was quoted as saying by Purdue.
After discovering the potential for habitable environments in Jezero Crater’s aged lava flows, which is considered uninhabitable, scientists have big hopes that they will find something great in the sedimentary rocks Perseverance is now examining.
Horgan said they are excited to see “even better results about organics and ancient habitable environments”. “I think it’s really setting the stage that Mars is this watery, habitable place, and all the samples we’re getting back are going to help us understand the history of ancient microbial life on Mars.”
Perseverance is now drilling and collecting core samples of the sedimentary rocks which the Mars Sample Return campaign could bring to Earth to be studied by powerful lab equipment, NASA said.