WASHINGTON D.C. — The Perseverance Rover on Mars may have stumbled upon the oldest rocks humans have ever seen and, possibly, evidence of a new setting that ancient Martian organisms could have inhabited, if they ever existed.
“This is really one of the most exciting things that this mission is going to do, is to be looking at rocks that were formed so early in the history of the solar system,” said Caltech geochemist Kenneth Farley during a December 12 news briefing at a meeting of the American Geophysical Union. “Almost the dawn of the solar system.”
Possibly the oldest rocks we’ve seen
For most of its mission, Perseverance has been poking around within Jezero Crater, probing and sampling rocks that are probably about 3.7 billion years old (SN: 2/17/23). The rocks at the rim, however, are probably much older, having been uplifted by the impact that created the crater.
On December 11 — following a slippery, three-month-long, 500-meter climb from the crater floor — the robotic explorer finally surmounted that crater’s rim, after weeks of studying the high area’s geology. And all that exploration appears to have paid off.
“The rocks that we are now exploring are likely older than 4 billion years,” said Farley, who is also project scientist for the Mars 2020 Mission that brought the rover to the planet. “These are amongst the oldest rocks in the solar system, and they’re older than any rocks that exist on Earth.” Part of the reason for that is that much of Earth’s ancient surface has been destroyed at subduction zones, where one tectonic plate plunges beneath another to descend into the mantle (SN: 1/13/21).
At the top of the crater, Perseverance traveled through an area known as the Pico Turquino Hills, where it captured images of numerous outcrops. “What we found in these relatively small outcrops is that the rocks are extremely diverse, and it appears that each one of the hills that make up the Pico Turquino Hills have a distinct assemblage of largely igneous minerals, with some alteration by water,” Farley said. “These are likely pieces of the earliest crust of Mars.”
Instruments aboard Perseverance cannot precisely date the rocks. Instead, researchers are basing their age estimates on their current understanding of the crater’s formation and Mars’ history. “They are our best estimates, but they are just estimates,” Farley said. “This is one of the reasons why we want to do sample return.”
If the newly encountered Martian rocks are really that old, they could contain information about how rocky planets like Mars and Earth evolved in their infancy (SN: 3/16/17). “For us to understand how rocky planets behave in that first, say, half a billion years, [we] can’t do it from Earth,” Farley said.
A new potential setting for Martian life
Ancient rocks weren’t all that Perseverance found in the Pico Turquino Hills. The rover also came across evidence of a completely new habitable setting for possible Martian life (SN: 7/15/24): a field of “brilliant white, cantaloupe-sized [stones], and the instruments aboard the rover confirm that these cobbles are pure quartz,” Farley said. “This has never been seen before” on Mars.
Quartz forms in places where hot fluids circulate through rocks, and sometimes at temperatures that are habitable. These rocks may have formed in a setting akin to a hot spring, and we know those environments can support life on Earth, so perhaps something similar once existed on Mars, Farley said. “This is a potentially habitable environment that’s totally different from the habitable environments that Perseverance investigated on the crater floor.”
According to Farley, the goal is to now search for quartz where it is still embedded in the Martian surface, so it can be sampled. “Neither our drill nor our abrader can actually operate on such loose, [cobblestone-sized rocks],” Farley said. “The rock would just move out of the way if we try to work on it.” Finding easier-to-access quartz could also help researchers better understand how the mineral fits into the rest of the Martian rock record.
Next stop, Witch Hazel Hill
Moving on from the Pico Turquino Hills, Perseverance will spend the next six months exploring an area called Witch Hazel Hill. Located away from the crater, the rocks at Witch Hazel Hill should be more representative of the geology of the broader region beyond, said planetary scientist and geologist Candice Bedford of Purdue University in West Lafayette, Ind., at the news briefing.
What’s more, NASA’s Mars orbiters have already identified extensive outcropping of layered rocks at Witch Hazel Hill. “As geologists we love layered outcrops,” Bedford said. “For us, every layer preserved is like, as we look down through that, it’s like turning a [page in the book] of Martian history.”
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