On the surface of Mars, a rover has filled over two dozen airtight titanium tubes with pristine rock samples, each a little thicker than a pencil.
Some tubes have been stashed on the Red Planet's surface, while others are held inside the rover's belly. NASA and the European Space Agency are planning to return some of these precious rock samples to Earth, the culmination of a decades-long dream to retrieve pristine rocks from Mars.
The ambitious, multi-billion-dollar effort, however, has been plagued by concerns about ballooning costs.
Now, in a press briefing held Tuesday, NASA officials said that the agency was going to simultaneously explore two different mission plans, and hold off on making the final decision about which one to actually pursue until the second half of 2026.
One of the two options would use tried-and-true methods for landing on Mars demonstrated by past rover missions, such as the "sky crane," but would require using a smaller ascent vehicle than previously envisioned to get the rocks off of the planet.
The second option would rely on commercial launch and landing capabilities that aren't yet fully developed, but show promise.
Each of these two options would be "simplified, faster, and less expensive" compared to the original plan, said NASA administrator Bill Nelson.
"We want to have the quickest, cheapest way to get these 30 samples back," said Nelson. "We want to return 30 titanium tubes as soon as possible at the cheapest price."
Previously, the Mars Sample Return mission had been estimated to cost around 11 billion dollars and would not return a sample until the 2040's, noted Nelson, who said a re-evaluation of the mission had to be done because "this thing had gotten out of control."
He said that either of these two new options would cost in the range of 6 to 7 billion dollars and could return a sample by 2039.
While some experts recommended returning the samples into orbit around the moon where they could be retrieved later, NASA officials preferred a direct return to Earth, in part because "it reduces complexity," said Nicky Fox, associate administrator of NASA's science mission directorate.
"My priority is to find a path forward for Mars Sample Return within a balanced overall science program," said Fox. "All of these new possibilities that we've outlined today will help us achieve that."
Both of the two new options under consideration would redesign the mission's landing platform and sample loading systems. But each would still rely on an orbiter being built by the European Space Agency that would capture the sample container in space near Mars and return it to Earth.
She said over the next year or so, teams would be working on the engineering for each proposed plan.
This decision to pursue two separate pathways comes after the agency requested proposals for lowering the mission's cost and complexity in April, and after they recently consulted with outside experts about the different possible ways of moving forward.
It's unclear what incoming president Donald Trump and his pick to head NASA, entrepreneur and private astronaut Jared Isaacman, will think of all of this—to say nothing of Congress, which holds the purse strings.
But what is clear is that the rocks stored on Mars are a tantalizing collection of geologic treasures that lab scientists could search for signs of ancient microbial life.
While Mars rocks do occasionally come to Earth as meteorites, these are rare and have been altered by their time in space and their fiery entry through Earth's atmosphere.
Pristine Mars rocks, in contrast, could tell planetary scientists far more about the history of Mars and the likelihood that life evolved there. That's why getting such a sample has long been a top priority for researchers—although they have also worried that if costs get out of hand, the project might draw funds away from other important science missions.
When the Perseverance rover launched in 2020, it carried along with it the tools and mechanisms needed to collect and store rocks. The rover landed on Mars in 2021 and soon drilled its first rock sample.
Since then, as the rover has trundled through the alien dirt, its controllers have ordered the robot to collect samples of particularly intriguing rocks and seal them up for safekeeping, creating a carefully-curated collection.
While robotic missions have returned samples from the moon, a comet, and asteroids, no mission has ever returned rocks and dirt from another planet.
The prospect is daunting and poses technical challenges. For example, mission planners will need to ensure that nothing from Mars could end up contaminating the Earth.
Nelson noted that China was pursuing what he called a "grab and go" mission to return a sample from Mars, and that the ultimate decisions about what NASA does will get made by officials in the incoming administration.
"I think it was a responsible thing to do, not to hand a new administration just one alternative, if they want to have a Mars sample return, which I can't imagine that they don't," says Nelson. "I don't think we want the only sample return coming back on a Chinese spacecraft."
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