Why did rocks from the Mars Perseverance rover surprise scientists?

Rocks collected by the Mars rover could help scientists figure out if Mars could support life and, if so, when.

NASA’s Perseverance Mars rover took this selfie near rock nicknamed “Rochette,” found on Jezero Crater’s floor, on Sept. 10, 2021, the 198th Martian day, or sol, of the mission. (photo credit: NASA/JPL-Caltech/MSSS)
NASA’s Perseverance Mars rover took this selfie near rock nicknamed “Rochette,” found on Jezero Crater’s floor, on Sept. 10, 2021, the 198th Martian day, or sol, of the mission.
(photo credit: NASA/JPL-Caltech/MSSS)

Groundbreaking new rock samples collected by NASA's Perseverance rover on Mars have provided surprising new discoveries already according to a new paper published in the peer-reviewed journal Science on Thursday, although scientists will need to wait a decade in order to fully study the rocks once they arrive on Earth.

The paper is a summary of three more in-depth papers published simultaneously in Science and Science Advances.

The rocks were collected in the Jezero Crater, an area targeted by NASA as it appears to contain a river delta and a lake and could be the best bet for scientists to learn about the geological and water history of the Red Planet.

Studying the chronology of Mars's rocks could also help scientists figure out when there was a lake at the site and when environmental conditions could have supported life, explained geochemist David Shuster, professor of earth and planetary science at the University of California, Berkeley, and a lead author of the study.

The rocks were collected from four sites on the floor of the crater — two sites referred to as Séítah (the Navajo word for “amidst the sand”) and two sites referred to as Máaz (Mars in the Navajo language).

 NASA’s Perseverance Mars rover looks out at an expanse of boulders on the floor of Jezero Crater in front of a location nicknamed “Santa Cruz” on Feb. 16, 2022, the 353rd Martian day, or sol, of the mission. (credit: NASA/JPL-Caltech/ASU/MSSS) NASA’s Perseverance Mars rover looks out at an expanse of boulders on the floor of Jezero Crater in front of a location nicknamed “Santa Cruz” on Feb. 16, 2022, the 353rd Martian day, or sol, of the mission. (credit: NASA/JPL-Caltech/ASU/MSSS)

Collected samples ideal for discovering the chronology of water on Mars

The samples collected are all igneous cumulate rocks - rocks formed by the cooling of molten magma - which is the ideal rocks for precise geochronology once they're returned to Earth. The rocks also show signs of having been altered by water.

“From a sampling perspective, this is huge,” said Shuster in a press release. “The fact that we have evidence of aqueous alteration of igneous rocks — those are the ingredients that people are very excited about, with regard to understanding environmental conditions that could potentially have supported life at some point after these rocks were formed.”

Geochemist Kenneth Farley of Caltech, Perseverance’s project scientist and another lead author on the paper, added that the rocks show that the lake in the crater was there after the igneous rocks formed.

“This will address some major questions: When was Mars’ climate conducive to lakes and rivers on the planet’s surface? And when did it change to the very cold and dry conditions we see today?” said Farley.

The rocks at the Séítah sites appear to have formed underground and cooled slowly, with whatever was covering them has eroded away over the past 2.5-3.5 billion years. The rocks may have also been formed by a magma lake that filled up the crater and cooled gradually.

What makes these rocks special?

The samples taken at the Máaz sites have a different composition from those at the other sites but are still igneous. The rocks come from a layer that overlies the layer of rock at the Séítah sites, showing that they may have come from the upper layer of a magma lake. They could also be from a later volcanic eruption.

Dr. David Flannery from the QUT Faculty of Science and QUT Planetary Surface Exploration research group explained that the samples will allow researchers a better understanding of warmer and wetter periods in Mars' past and any evidence for past life.

“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,” said Flannery.

“Ancient igneous rocks will allow us to date a several billion-year-old rock with very high precision... 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.”

"If we find that this lake was a habitable environment, for example, we will have an age constraint on when it was habitable."

Dr. David Flannery from the QUT Faculty of Science and QUT Planetary Surface Exploration research group

The rocks collected were altered by water

While the rocks collected at all sites showed signs of having been altered by water, they were altered in different ways. The Máaz rocks contained pockets of minerals that may have condensed from salty brine, while the Séítah rocks had reacted with carbonated water.

Flannery added that on Earth, reactions of igneous rocks with water produce diverse habitats for microbial life. The rocks collected by Perseverance seem to have similar characteristics and could record biosignatures of ancient habitats.

When will the rocks to return to Earth?

The rocks will be carried off of Mars by the Sample Retrieval Lander which will transfer them to the Earth Return Orbiter, with the rocks expected to land back on Earth in 2033.

“There are a variety of different geochemical observations that we can make in these rocks when we return them to Earth. That will give us all sorts of information about that igneous environment,” said Shuster.

“We can figure out when the rock crystallized, which is one of the things that I'm most excited about for providing a delta timing constraint. But it also gives us information about when igneous activity was occurring in the planet’s interior. Combined with satellite imagery, we can then relate that to some of the bigger-picture, more regional igneous activity,” he said. 

Duplicate rock samples were collected at all the sites and will be cached along with other duplicate samples at a contingency site near the delta in case the samples onboard the rover become inaccessible. The cache will also include recently collected samples of sediments from the delta.

“Mars is another example of how things can pan out, and things did pan out quite differently."

Dr. David Flannery from the QUT Faculty of Science and QUT Planetary Surface Exploration research group

“Mars is another example of how things can pan out, and things did pan out quite differently," explained Flannery. "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.”

Perseverance landed on Mars in February 2021.