Research Determines Original Orientations of Rocks Drilled on Mars

Navigating an archaic lakebed on Mars, NASA’s Perseverance rover is amassing a unique collection of rocks. The car-sized explorer is methodically drilling into the Red Planet’s surface, extracting cores of bedrock that it stores in sturdy titanium tubes. Scientists hope to one day return the tubes to Earth and analyze their contents for signs of embedded microbial life.

Since touching down on Mars in 2021, the rover has filled 20 of its 43 tubes with bedrock cores. Now, MIT geologists have remotely determined a key property of the rocks collected so far that will support scientists answer key questions about the planet’s past.

In a research appears today in the journal, the MIT team reports that it has determined the original orientation of most of the bedrock samples collected by the rover so far. Using the rover’s own engineering data, such as the vehicle’s positioning and its drill bit, scientists could estimate the orientation of each bedrock sample before drilling it out of the Martian soil.

The results represent the first time scientists have oriented bedrock samples on another planet. The team’s method could be applied to future samples the rover collects as it expands its exploration beyond the archaic basin. Combining the orientations of multiple rocks in different locations could then give scientists clues about the conditions on Mars in which the rocks originally formed.

“There are so many scientific questions that require figuring out the orientation of the samples we bring back from Mars,” says study author Elias Mansbach, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

“The orientation of rocks can tell you something about any magnetic field that might have existed on the planet,” adds Benjamin Weiss, a professor of planetary science at MIT. “You can also study how water and lava flowed on the planet, the direction of past winds, and tectonic processes, such as what was lifted and what sank. So it’s a dream to be able to orient bedrock on another planet because it opens up so many scientific possibilities.”

Weiss and Mansbach’s co-authors include Tanja Bosak and Jennifer Fentress of MIT, as well as collaborators from numerous institutions, including the Jet Propulsion Laboratory at Caltech.

A profound change

The Perseverance rover, nicknamed “Percy,” is exploring the floor of Jezero Crater, a vast impact crater covered in layers of igneous rock that may have been formed by archaic volcanic eruptions, as well as sedimentary rocks that likely formed from long-dried rivers that flowed into the basin.

“Mars was once warm and wet, and there’s a good chance that life existed there once,” Weiss says. “Now it’s cold and dry, and something profound must have happened on the planet.”

Many scientists, including Weiss, suspect that Mars, like Earth, once had a magnetic field that protected the planet from the solar wind. Conditions then may have been favorable for water and life, at least for a time.

“When the magnetic field disappeared, the solar wind—this plasma that evaporates from the sun and moves faster than the speed of sound—just hit the Martian atmosphere and could have removed it over billions of years,” Weiss says. “We want to know what happened and why.”

Rocks beneath Mars’ surface likely hold a record of the planet’s past magnetic field. When rocks first formed on the planet’s surface, the direction of their magnetic minerals was set by the surrounding magnetic field. The orientation of rocks can therefore support reconstruct the direction and intensity of the planet’s magnetic field, and how it has changed over time.

As Perseverance collected samples of bedrock, as well as surface soil and air, as part of its exploration mission, Weiss, who is a member of the rover’s science team, and Mansbach looked for ways to determine the original orientation of the bedrock samples, which would be a first step toward reconstructing the history of Mars’ magnetic field.

“It was an amazing opportunity, but there was no initial mission requirement to orient the bedrock,” Mansbach notes.

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For months, Mansbach and Weiss met with NASA engineers to establish a plan to estimate the original orientation of each bedrock sample before drilling it out of the ground. The problem was a bit like trying to predict which way a petite circle of dough is pointing before screwing in a round cookie cutter to extract a piece. Similarly, to collect a bedrock sample, Perseverance screws a tube-shaped drill bit into the ground at a right angle, then pulls the drill straight back out, along with any rock it penetrates.

To estimate the orientation of a rock before drilling a hole in the ground, the team realized they needed to measure three angles: hade, azimuth, and roll, which are similar to the pitch, yaw, and roll of a boat. Hade is essentially the tilt of the sample, while azimuth is the absolute direction the sample is pointing relative to true north. Roll refers to how much the sample has to rotate before it returns to its original position.

Talking with NASA engineers, MIT geologists discovered that the three angles they needed were related to measurements the rover takes on its own during its normal operations. They realized that to estimate the hade and azimuth of the sample, they could employ the rover’s measurements of the drill’s orientation, because they could assume that the drill’s tilt was parallel to any sample it retrieved.

To estimate the sample’s rotation, the team used one of the rover’s onboard cameras, which takes a picture of the surface the drill is about to sample. They figured they could employ any distinguishing features in the surface image to determine how much the sample would have to rotate to return to its original orientation.

In cases where the surface showed no particular features, the team used the rover’s onboard laser to make an L-shaped mark on the rock before drilling a sample—an action jokingly described at the time as the first graffiti on another planet.

By combining all the rover’s positioning, orientation, and imaging data, the team estimated the original orientations of all 20 Mars bedrock samples collected so far, with accuracy comparable to the orientations of rocks on Earth.

“We know the orientations to within 2.7 degrees of uncertainty, which is better than what we can do with rocks in the Earth,” Mansbach says. “We’re now working with engineers to automate this orientation process so that it can be done with other samples in the future.”

“The next phase will be the most exciting,” Weiss says. “The rover will go beyond the crater to get the oldest known rocks on Mars, and this is an incredible opportunity to orient these rocks and hopefully uncover many of these ancient processes.”

This research was partially funded by NASA and the Mars 2020 Participating Scientist program.