Perseverance Rover Completes Depot of Mars Rock Samples

The collection is a failsafe for the Mars Sample Return project, which aims to deliver Martian rocks to Earth

Perseverance selfie
NASA's Perseverance Mars rover took this selfie with some of the sample tubes it left on the Red Planet's surface using the camera at the end of its robotic arm. NASA / JPL-Caltech / MSSS

NASA’s Perseverance rover has finished an important task in its exploration of the Red Planet: assembling a cache of Martian rock samples on the surface. One day, scientists may need retrieve these samples for further study back on Earth.

The rover spent the last six weeks creating this depot—ten tubes full of rocks that researchers have deemed “scientifically significant” for better understanding Mars. Scientists at NASA’s Jet Propulsion Laboratory got word that Perseverance had dropped its final tube on Sunday evening and announced the depot’s completion on Monday.

The sample depot is the first to ever be created on another planet, per NASA.

Ultimately, NASA and the European Space Agency (ESA) plan to bring Mars samples back to Earth. This cache on the surface will serve as a backup—the agencies’ plan A is to retrieve a duplicate group of rock samples collected by Perseverance and stashed aboard the rover itself. In 2028, the partnered space agencies hope to launch a Sample Retrieval Lander to Mars. Then, if all goes to plan, Perseverance will hand off its onboard sample tubes to a small rocket called the Mars Ascent Vehicle, which will carry the samples to orbit. Finally, the Earth Return Orbiter will bring them back to Earth. Based on the projected timeline, the samples could arrive on Earth as early as 2033, when they’d become available to scientists around the world for analysis.

But if Perseverance’s onboard cache cannot be recovered for some reason, scientists aren’t totally out of luck, thanks to the now-completed sample depot on the planet’s surface.

“The most challenging aspect of Mars Sample Return is just the long chain of events that all need to be successful,” said David Spencer, the Mars Sample Return mission manager, to Smithsonian magazine’s Theresa Machemer in February 2021. “We’re trying to build in robustness as much as we can.”

How to Bring Mars Sample Tubes Safely to Earth (Mars News Report)

To assemble the depot, Perseverance placed the ten 7-inch titanium tubes in a complex zigzag pattern, with all samples roughly 15 to 50 feet apart. Meanwhile, back on Earth, scientists carefully recorded the precise location of each tube in case they are coated in dust and not visible during any recovery mission in the future.

Perseverance created the cache on flat ground in the so-called Three Forks area of Jezero Crater, which scientists say was full of water several billion years ago. The depot is near the base of an ancient river delta that once flowed into Jezero Lake.

Researchers sent Perseverance to explore the 28-mile-wide Jezero Crater because of the area’s potential for evidence of ancient microbial life on Mars. If living things ever existed on the Red Planet, they may have inhabited areas with shallow water, like the Three Forks delta.

From the samples, which consist of igneous and sedimentary rock cores, researchers hope to learn more about the geological—and, possibly, astrobiological—processes that unfolded when the crater formed nearly four billion years ago. In addition to the tubes full of Martian rocks, Perseverance also created a “witness” tube, which will serve as a control to help determine if the samples were contaminated by materials from Earth that traveled to Mars aboard the rover.

Shadowy image of a tube on the ground
Perseverance deposited its first sample tube on the surface of Mars on December 21, 2022. NASA / JPL-Caltech / MSSS

With the depot now finished, the six-wheeled Perseverance rover will travel up the river delta via a previously explored route known as Hawksbill Gap. It will pass by an area called Rocky Top before exploring the top of the delta, which is new territory for the rover. Scientists are eager to explore this region, because it features different types of rocks that may offer additional insights into the Red Planet’s geological past.

“As we ascend the delta into a river setting, we expect to move into rocks that are composed of larger grains—from sand to large boulders,” says Ken Farley, a geochemist at California Institute of Technology who works on the Perseverance mission, in a statement. “Those materials likely originated in rocks outside of Jezero, eroded and then washed into the crater.”

Perseverance launched on July 30, 2020, and it arrived on the Red Planet on February 18, 2021. Along with gathering rock samples, the car-sized rover has also been imaging the planet’s surface and testing new technologies for possible future robotic and human missions to Mars.

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