The rover discovered that the bottom of Jezero Crater is made of volcanic rock that interacts with water.
When NASA’s Perseverance Mars rover began examining rocks at the floor of Jezero Crater in the spring of 2021, scientists were taken aback: Because the crater had a lake billions of years ago, they had expected to find sedimentary rocks, which Sedimentary rocks form when sand and mud settles in a once-wet environment. Instead, they found that the floor was made of two types of igneous rocks — one formed by magma deep underground and the other formed by volcanic activity at the surface.
The findings are described in four new papers published Thursday, August 25. In the journal Science, an article outlines Perseverance’s exploration of the crater floor before reaching Jezero’s ancient river delta in April 2022; a second study in the same journal details what appears to be a thick Unique rock formed from magma. Two other papers published in Science Advances detail the unique way Perseverance’s rock-vaporization laser and ground-penetrating radar determined that igneous rock covers the crater floor.
Stone of the Century
Igneous rocks are excellent timekeepers: crystals within them record details of the precise moment they formed.
“A great value of the igneous rocks we collect is that they will tell us when Lake Jezero came into being. We know it formed later than the rocks at the bottom of the igneous crater,” said Caltech’s Ken Farley, a project scientist at Perseverance , and lead author of the first new scientific paper. “This will address some major questions: When did Mars’ climate favor lakes and rivers on Earth’s surface, and when did it turn into the very cold and dry conditions we see today?”
However, because of the way it formed, igneous rock is not suitable for preserving the potential signs of ancient microscopic life that Perseverance is looking for. By contrast, determining the age of a sedimentary rock can be challenging, especially when it contains rock fragments that formed at different times before the rocky sediments were deposited. But sedimentary rocks typically form in aquatic environments suitable for life and are better at preserving ancient signs of life.
That’s why the sediment-rich river delta that Perseverance has been exploring since April 2022 has been so enticing to scientists. The rover has already begun drilling and collecting core samples of sedimentary rocks there, so that the Martian sample return campaign could potentially return them to Earth for study by powerful laboratory equipment too large to take to Mars.
Mysterious lava rocks
The second paper, published in the journal Science, solves a long-standing mystery on Mars. Years ago, a Mars orbiter discovered a rock formation filled with the mineral olivine. About 27,000 square miles (70,000 square kilometers) — almost the size of South Carolina — this formation extends from the inner edge of Jezero Crater to the surrounding area.
Scientists have proposed various theories as to why olivine is so abundant over such a large surface area, including meteorite impacts, volcanic eruptions and sedimentary processes. Another theory is that olivine formed deep underground from slowly cooling magma (lava), which was then exposed by erosion over time.
Yang Liu of NASA’s Jet Propulsion Laboratory in Southern California and her co-authors have determined that this last explanation is the most likely. Perseverance grinds away a stone to reveal its composition; by studying the exposed patches, scientists have focused on the large grain size of olivine and the chemical composition and texture of the rock.
Using Perseverance’s Planetary Instrument for X-ray Petrochemistry (PIXL), they determined that the region had olivine grains ranging from 1 to 3 millimeters in size—much larger than expected for olivine formed in rapidly cooling lava on the planet’s surface.
“This large crystal size and its uniform composition in a specific rock texture requires a very slow cooling environment,” Liu said. “So, most likely, Jezero’s magma did not erupt at the surface.”
Unique scientific tools
Two Science Advances papers detail the discovery of scientific instruments that helped pinpoint the igneous rock covering the bottom of the crater. These instruments include Perseverance’s SuperCam laser and a ground-penetrating radar called RIMFAX (Radar Imager for Underground Experiments on Mars).
Equipped with a rock vaporization laser, the SuperCam can hit targets as small as the tip of a pencil at a range of up to 20 feet (7 meters). It uses a visible light spectrometer to study the steam produced to determine the chemical composition of the rock. The SuperCam scored 1,450 points in Perseverance’s first 10 months on Mars, helping scientists draw conclusions about the igneous rocks at the bottom of the crater.
In addition, SuperCam used near-infrared light — the first instrument on Mars with this capability — to find that water changed minerals in the rocks at the bottom of the crater. However, these changes were not widespread across the crater floor, according to a combination of laser and infrared observations.
“SuperCam’s data suggest that these rock formations either separated from Jezero’s lake waters or that the lake existed for a limited time,” said Roger Wiens, SuperCam’s principal investigator at Purdue University and Los Alamos National Laboratory.
RIMFAX marks another first: Mars orbiters carry ground-penetrating radar, but no spacecraft on the surface of Mars before Perseverance. On the surface, RIMFAX can provide unparalleled detail and measure crater bottoms as deep as 50 feet (15 meters).
Its high-resolution “radar map” shows rock formations sloping an unexpected 15 degrees into the ground. Knowing how these rock layers are arranged could help scientists establish a timeline of the formation of Jezero Crater.
“As the first instrument of its kind to operate on the surface of Mars, RIMFAX demonstrates the potential value of ground-penetrating radar as a subsurface exploration tool,” said Svein-Erik Hamran, principal investigator of RIMFAX at the University of Oslo, Norway.
The scientific team is excited about their discoveries so far, but they are even more excited about future science.
More about Mission
A key goal of the Perseverance Mars mission is astrobiology, including the search for signs of ancient microbial life. The rover will describe Mars’ geology and past climate, pave the way for human exploration of the Red Planet and be the first mission to collect and store Martian rock and regolith (broken rock and dust).
Subsequent NASA missions, in partnership with ESA (European Space Agency), will send spacecraft to Mars to collect these sealed samples from the surface and send them back to Earth for in-depth analysis.
The Mars 2020 Perseverance mission is part of NASA’s approach to moon-to-Mars exploration, including the Artemis lunar mission, which will help prepare humans for exploration of the Red Planet.
JPL is managed for NASA by Caltech in Pasadena, California, building and managing the operations of the Perseverance rover.
More on perseverance:
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