MIT Study Unlocks Original Mars Rock Orientations

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Which direction a rock faces matters more than you’d think. Researchers at MIT have spent the last several months working to understand the original orientations of rocks on Mars, starting with bedrock samples collected by NASA’s Perseverance rover. Their method, which nails down rocks’ orientations within 2.7 degrees of uncertainty, could help astronomers better understand the Red Planet’s sediment, ancient magnetic field, tectonic processes, and more.

Perseverance’s data makes it all possible. In a study published Monday in Earth and Space Science, MIT researchers and experts at the Jet Propulsion Laboratory (JPL) at Caltech write that Perseverance—the star of NASA’s Mars 2020 mission—wasn’t designed to orient the bedrock samples it drilled from Mars’ surface. Understanding the original positioning of each rock requires a bit of reverse engineering: A process only made viable by the rover’s coring drill and wide-angle topographic sensor for operations and engineering (WATSON) camera.

Every time Perseverance obtains a bedrock sample, it angles its arm’s percussive coring drill at the Red Planet’s terrain. Before Perseverance stabilizes itself and shoves its drill into the ground, WATSON snaps a high-resolution image of the outcrop surface, the visibly exposed part. After drilling is complete, another picture is taken of the bottom of a sample. 

The Lefroy Bay core inside Perseverance’s drill bit.
Credit: NASA/JPL-Caltech/ASU

This data—the pictures taken before and after extraction and the angle of Perseverance’s drill—gives MIT and JPL a place to work backward. From there, the researchers determine three angles related to a given sample—the hade, azimuth, and roll—which they say are analogous to a boat’s pitch, yaw, and roll. While the tilt of a sample constitutes the hade, a sample’s azimuth is the absolute direction it’s pointing relative to true north. The roll describes how much a sample would turn to return to its original position. These angles allow the team to determine a rock’s original orientation with a certainty buffer of just 2.7 degrees.  

“Unlike Martian meteorites, the rocks sampled by the rover have geologic and stratigraphic contexts that constrain their formation and evolution,” the study’s authors write. They explain that orienting a sample relative to Martian geographic coordinates could reveal unprecedented insight into Martian geologic and geophysical processes, which are (or were) influenced by the Red Planet’s magnetic field, tectonic movements, and weather. 

MIT and JPL are now working to automate their process for future samples. 

“The next phase will be the most exciting,” said Benjamin Weiss, professor of planetary sciences at MIT. “The rover will drive outside [Jezero Crater] to get the oldest known rocks on Mars, and it’s an incredible opportunity to be able to orient these rocks, and hopefully uncover a lot of these ancient processes.”