Evrim Yazgin
Cosmos science journalist
NASA’s Perseverance rover has found rocks which might hold the key to understanding Mars’ geological history.
These are the first datable Mars rock samples so they will provide a landmark in geological time for mapping the history, evolution, and changing climate of the red planet.
The olivine cumulate is an igneous rock (formed when molten magma cools and crystallises) which was found below the sedimentary layer of the Jezero Crater where Perseverance has been conducting its surveys of Mars since it landed on February 18 last year.
Researchers from the Queensland University of Technology (QUT) are part of the team which is analysing the samples and published the discovery in Science.
Like a geological “Rosetta Stone,” the samples will be dated once returned to Earth and help place other geological and climatic events into context. The researchers believe the samples will give a better understanding of warmer and wetter periods in Mars’ past and will be important for any potential past life the mission may find.
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“It was a surprise that we didn’t find sedimentary rocks on the crater floor but also ideal because finding a datable igneous sample was one of the main mission goals,” says co-author Dr David Flannery, QUT researcher and long-term planner for the Perseverance mission.
“Ancient igneous rocks will allow us to date a several billion-year-old rock with very high precision. This will provide important timing and duration constraints on the history of Jezero crater and its surrounding region.
“So effectively, we landed on exactly the thing we needed to help us with one of our other main goals, which is to find evidence of past life. If we find that this lake was a habitable environment, for example, we will have an age constraint on when it was habitable.”
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On Earth, igneous rocks can react with water to produce diverse habitats for microbial life.
Early signs from Perseverance show rocks on the floor of the 45-kilometre wide Jezero crater appear to share the same characteristics and may potentially record biosignatures of ancient ecosystems.
The olivine sample was identified by the QUT-developed Planetary Instrument for X-ray Lithochemistry (PIXL) tool aboard the Perseverance rover. PIXL was able to determine the composition and mineralogy, including diffraction peaks – changes in the atomic structure of the rock.
Once data was collected by the car-sized rover, it was sent back to Earth and analysed by Flannery’s team at QUT.
“Our working hypothesis was that we were at the bottom of a lake because sedimentary features viewed from orbit suggested the crater was under water at some point,” says Flannery. “Now we know we’re looking at olivine, which on Earth, would be pushed towards the surface from the mantle through tectonic processes – volcanos and lava flows.”
“This discovery is hugely important because these types of rocks can be dated with radiometric techniques, the same as we use on Earth to date very old rocks.”
In a second study published in Science, researchers explain how the discovery inside the crater helped solve a long-standing mystery of an olivine-rich outcrop spanning 70,000 square kilometres from the edge of Jezero into the surrounding region.
The olivine sample resembles Martian meteorites found on Earth and were found after Perseverance created an abrasion patch by grinding away surface material.
The olivine has a large crystal size and uniform compositionand it is believed it formed in a very slow cooling environment. The researchers theorise that magma in Jezero did not erupt to the surface but formed underground before being exposed over time by erosion.
Flannery says that in the distant past Mars may have been habitable.
“Mars is another example of how things can pan out, and things did pan out quite differently. It sort of died off geologically. It doesn’t have plate tectonics anymore, for example. And climate change has led to the cold and dry conditions that we have on the surface today.
“Being able to date these old rocks on Mars allows us to unravel its history. Studying Mars helps us put the Earth in context and gives us a mirror to better understand how our planet might be special.”
After being thwarted in January by an errant rock and hit by a wind-blown pebble in July, the discovery delighted supporters of the plucky rover which has persevered through trials and tribulation to deliver valuable scientific data.
With planned launch dates for the Earth Return Orbiter and Sample Retrieval Lander in 2027 and 2028, respectively, the samples are expected to arrive on Earth in 2033.