The rover found that the floor of Jezero Crater is made up of volcanic rocks that have interacted with water.
Scientists got a surprise when NASA’s Perseverance Mars rover began examining rocks on the floor of Jezero Crater in the spring of 2021: Because the crater contained a lake billions of years ago, they expected to find sedimentary rocks, which would have formed when sand and mud settled in a formerly watery environment. Instead, they discovered that the ground was made up of two types of igneous rock – one that formed deep underground from magma, the other from volcanic activity on the surface.
The findings are described in four new articles published Thursday, August 25. In Science, we offer an overview of Perseverance’s exploration of the crater floor before its arrival in the ancient Jezero River Delta in April 2022; a second study in the same journal details distinctive rocks that appear to have formed from a thick body of magma. The other two papers, published in Science Advances, detail the unique ways in which Perseverance’s rock vaporization laser and ground-penetrating radar established that igneous rocks line the crater floor.
rock of ages
Igneous rocks are excellent timekeepers: the crystals they contain record details of when they were formed.
“One of the great values of the igneous rocks we collected is that they will tell us when the lake was present at Jezero. We know that it was there more recently than the igneous rocks at the bottom of the crater formed” , said Ken Farley of Caltech, a scientist with the Perseverance project and lead author of the first of the new scientific papers. “It will answer some major questions: when was the climate of Mars suitable for lakes and rivers on the surface? of the planet, and when did it change to the very cold and dry conditions that we have today?”
However, due to the way it forms, igneous rock is not ideal for preserving the potential signs of ancient microscopic life that Perseverance seeks. In contrast, determining the age of a sedimentary rock can be difficult, especially when it contains rock fragments that formed at different times before the rock sediment was deposited. But sedimentary rocks often form in aquatic environments that support life and are better able to preserve the old signs of life.
That’s why the sediment-rich river delta that Perseverance has been exploring since April 2022 is so tempting to scientists. The rover began drilling there and collecting sedimentary rock cores so that the Mars Sample Return campaign could potentially send them back to Earth to be studied by powerful laboratory equipment too large to bring to Mars.
Mysterious rocks formed from magma
A second paper published in Science solves a long-standing Mars mystery. Years ago, Mars orbiters spotted a rock formation filled with the mineral olivine. Measuring approximately 27,000 square miles (70,000 square kilometers) – almost the size of South Carolina – this formation stretches from the inner rim of Jezero Crater to the surrounding region.
Scientists have offered 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 the slow cooling of magma – molten rock – before being exposed over time by erosion.
Yang Liu of NASA’s Jet Propulsion Laboratory in Southern California and his co-authors determined that the latter explanation is the most likely. Perseverance abraded a rock to reveal its composition; Studying the exposed plot, the scientists focused on the large grain size of the olivine, as well as the chemistry and texture of the rock.
Using Perseverance’s Planetary Instrument for X-Ray Lithochemistry, or PIXL, they determined that the olivine grains in the area are 1 to 3 millimeters in size – much larger than one might expect. Wait for the olivine that formed in the rapidly cooling lava on the planet’s surface.
“This large crystal size and uniform composition in a specific rock texture requires a very slowly cooling environment,” Liu said. “So most likely this magma at Jezero did not erupt to the surface.”
Unique scientific tools
The two Science Advances articles detail discoveries of scientific instruments that helped establish that igneous rocks line the floor of the crater. Instruments include Perseverance’s SuperCam laser and a ground-penetrating radar called RIMFAX (Radar Imager for Mars’ Subsurface Experiment).
SuperCam is equipped with a rock vapor laser that can zap a target as small as a pencil tip up to 20 feet (7 meters) away. He studies the resulting vapor using a visible light spectrometer to determine the chemical composition of a rock. SuperCam removed 1,450 points during the first 10 months of Perseverance on Mars, helping scientists reach their conclusion about the igneous rocks at the bottom of the crater.
Additionally, SuperCam used near-infrared light – the first instrument on Mars with this capability – to find that water was altering minerals in rocks on the crater floor. However, the alterations were not ubiquitous throughout the crater floor, according to the combination of laser and infrared observations.
“The SuperCam data suggests that these rock layers were isolated from the water of Lake Jezero or that the lake existed for a limited time,” said Roger Wiens, SuperCam principal investigator at Purdue University and the Lab. Los Alamos National.
RIMFAX marks another first: Mars orbiters carry ground-penetrating radars, but no spacecraft on the surface of Mars have them before Perseverance. Being on the surface, RIMFAX can provide unparalleled detail and has probed the crater floor down to 50 feet (15 meters).
Its high-resolution “radargrams” show unexpectedly tilted rock layers up to 15 degrees underground. Understanding how these rock layers are ordered can help scientists establish a timeline for Jezero Crater’s formation.
“As the first instrument of its kind to operate on the surface of Mars, RIMFAX demonstrated the potential value of ground-penetrating radar as a tool for subterranean exploration,” said researcher Svein-Erik Hamran. principal of RIMFAX at the University of Oslo in Norway. .
The science team is excited about what they’ve discovered so far, but they’re even more excited about the science ahead.
Learn more about the mission
A key focus of Perseverance’s mission to Mars is astrobiology, including searching for signs of ancient microbial life. The rover will characterize the planet’s past geology and climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust).
Subsequent NASA missions, in cooperation with the ESA (European Space Agency), would send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for further analysis.
The Mars 2020 Perseverance mission is part of NASA’s Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.
JPL, which is managed for NASA by Caltech in Pasadena, Calif., built and manages operations of the Perseverance rover.
To learn more about perseverance:
Jet Propulsion Laboratory, Pasadena, California.