A rover has been collecting rocks from Mars for years. How will they get back to Earth?

A collection of Martian rocks could reveal details about potential past life on the Red Planet – but first NASA has to get them back to Earth.

For years, the U.S. space agency's Perseverance rover has been scouring Mars and scooping up intriguing rock samples. Some of those samples have been stashed away in cylindrical tubes on the planet's surface, while others are safely tucked away within the rover.

NASA and the European Space Agency have long yearned to transport at least some of those rocks to Earth for in-depth study. But ballooning costs and mission delays had begun to make the goal of returning the samples within the 2030s seem impossible.

So, the agency stepped back months ago to regroup and reevaluate.

Now, it appears the final say on the plan to get those Martian rocks to Earth will be made under President-elect Donald Trump's administration.

Earlier this month, outgoing NASA Administrator Bill Nelson and other agency officials presented two possible plans for the mission, known as Mars Sample Return, for the incoming administration to consider next year. That means when Trump takes office Monday, his pick to lead the agency – most likely billionaire entrepreneur and private astronaut Jared Isaacman, who last year led the Polaris Dawn mission – will have a major say in the final decision.

While robotic missions have returned samples from the moon and space rocks like asteroids, a successful Mars mission would mark the first time that rocks from another planet made it back to Earth. And once the samples are in the hands of scientists, the experts hope to study them to learn about the geological history of the now-barren planet, including whether life ever thrived.

"NASA’s rovers are enduring Mars’ harsh environment to collect ground-breaking science samples,” Nicola Fox, associate administrator of NASA’s Science Mission Directorate, said in a statement. “We want to bring those back as quickly as possible to study them in state-of-the-art facilities."

Here's everything to know about the Mars rock samples, potential plans to get them to Earth and what's next for Perseverance:

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What are the Mars rock samples?

In July 2020, the Perseverance rover underwent a 200-day, 300-million-mile journey to reach Mars. After landing in February 2021 in the Jezero Crater, the robot, controlled remotely from Earth, has since spent nearly four years searching for and collecting more than two dozen rock samples – many of which are stored at the first-ever depot on another planet for NASA and the ESA to one day retrieve.

The bottom of the Jezero Crater – believed to have formed 3.9 billion years ago from a massive impact – is considered to be among the most promising areas on Mars to search for evidence of ancient life.

Perseverance's adventures have revealed some insights about the enigmatic Martian geology, but nothing like what studying rocks up close with state-of-the-art equipment could unveil. And while Mars rocks do occasionally come to Earth as meteorites, such events are not only rare, but result in objects that have been altered during their spaceflights and fiery entry into our atmosphere.

For those reasons, NASA and the ESA are adamant about retrieving the pristine Mars rocks that Perseverance has amassed.

"These samples have the potential to change the way we understand Mars, our universe, and – ultimately – ourselves," Nelson said in a statement.

NASA's 2 options to return Martian rocks

To ensure that the goal of returning Mars samples in the 2030s remains on track, NASA in April 2024 sought other options to the roughly $11 billion plan the agency had been pursuing.

After 11 proposals were put before NASA in September, the agency appointed a review team to make final recommendations. NASA on Jan. 7 then unveiled the two mission plans estimated to cut costs to between an estimated $6 and $7 billion that agency officials believe offer the best chance of ensuring the samples arrive well before astronauts venture to Mars.

The more traditional option would involve the sky crane system, which is the same method that used a hovering rocket to lower NASA’s Perseverance and Curiosity rovers via cable onto the Martian surface. The second option would include a landing system developed by private companies.

Under each plan, the number of spacecraft and launches would remain the same, as an orbiter built by the European Space Agency would be tasked with bringing the rocks back. But NASA said the proposed plans would simplify the overall mission.

NASA said a final decision would come in the second half of 2026 following engineering studies into details of each plan.

"Pursuing two potential paths forward will ensure that NASA is able to bring these samples back from Mars with significant cost and schedule saving," Nelson said.

What's next for Perseverance on Mars?

As for Perseverance, the rover's hunt for Martian rocks is far from over.

After years in the trenches of Jezero, Perseverance in December finally summitted the steep Martian crater to begin the next leg of its journey exploring Mars.

Perseverance had begun its slow ascent in August 2024 to the top of the crater, which scientists believe was once flooded with water. The arduous climb, which took well over three months, was a journey filled with perilous obstacles – but also moments of discovery and awe as the six-wheeled robot stopped along the way to survey its surroundings.

Upon reaching the rim, ahead of the rover was a quarter-mile drive to another area where orbital data shows is rife with light-toned, layered bedrock, according to NASA. In the next year, the rover is expected to visit as many as four sites in a span of four miles to collect samples along the northern part of the southwestern section of Jezero's rim.

The first phase at the bottom of the crater focused on hunting for rocks believed to have partially filled the crater during its formation, NASA has said. Now, Perseverance will be looking for rocks believed to have originated from deep inside Mars that, after the crater-forming impact, were thrown upward to form the rim.

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at [email protected]

This article originally appeared on USA TODAY: Mars rock sample return: NASA proposes 2 plans for Trump to consider