At the University of Arizona's Biosphere 2, a small, airtight habitat is yielding greater understanding about how humans might one day survive far beyond Earth and on Mars. For the past two weeks, one researcher lived sealed inside the Space Analog for the Moon and Mars, or SAM, sharing his quarters with 144 dwarf pea plants.

The goal of the project was to measure how much carbon dioxide the pea plants could remove from the air and how much oxygen they could return in a closed system sustained only by sunlight, water and human breath.

"We need places like this to do the science that will help us survive off world," said Matthias Beach, who played the role of an astronaut during the simulated mission. "Some people might think we're decades away from that, but we're not. In the next 30 to 40 years, someone is going to Mars – it's inevitable. This is real science, and I'm so proud to be part of it."

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The experiment, directed by SAM research director Kai Staats, marks the first bioregenerative life-support trial with a human participant at Biosphere 2 since 1994.

The research occurred in tandem with the international World's Biggest Analog project, a coordinated two-week mission spanning from Oct. 13-27 that connected 16 space-habitat analogs across four continents. While crews elsewhere tested operations and psychology, Staats' focus was verifying whether plants can reliably manage air quality for humans during long-term missions off-Earth.

During the first week of the mission, the dwarf pea plants sequestered Beach's exhaled carbon dioxide through photosynthesis, a process in which the plants convert carbon dioxide and light into oxygen and carbohydrates. On the morning of Day 8, he harvested the plants, which were removed from the habitat through the airlock for external processing and analysis. The second week became a controlled contrast to track the rise in carbon dioxide levels with no plants in the habitat.

Inside SAM's test module, sensors embedded within each of the four compartments continuously monitored carbon dioxide. With the data, researchers can calculate precisely how much carbon each of the 144 pea plants removed from the air, giving an exact per-plant sequestration rate.

Dwarf pea plants produce a high seed yield in a small footprint, allowing astronauts to grow nutritious, protein-rich food in tightly packed spaces. That yield also makes the system self-sustaining as a portion of each crop's seeds can restart the next generation, reducing dependence on Earth-supplied resources.

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High productivity also means high carbon efficiency. Every additional plant represents carbon pulled from the air and locked into organic matter. This is a measurable gain for both food and oxygen supply. 

"You only have so many inches between the hydroponic racks," Staats said. "A full pea plant would be almost two meters tall. So, you're going to want a dwarf pea plant that produces a similar amount of fruit and similar amount of oxygen that doesn't take up as much space. Dwarf varieties are always preferred."

The hydroponic racks, managed by graduate student Atila Meszaros with guidance from the U of A's Controlled Environment Agriculture Center, automate water, light and nutrient delivery while keeping environmental parameters stable. SAM's sealed environment ensures that no outside air dilutes the data, a necessity when tracking subtle changes in gas concentration.

Each plant dataset will inform a broader 22-crop database Staats and his team are building. The open scientific resource will catalogue how different plant species perform in closed environments. When complete, the database could inform future mission planners exactly how many plants are needed to support a human crew and how much carbon those crops can safely recycle.

"There are 22 food cultivars such as peas, wheat, rice, barley, lettuce, cabbage, spinach, sweet potatoes and white potatoes," Staats said. "We are going to try and do all of them, so each plant will go through a similar program. Our goal is to build a rich, detailed database that space-faring entities, whether it's NASA, SpaceX, Blue Origin or others, can use to determine exactly how many square meters of each crop are needed to keep humans alive."

Now that Beach has completed his two-week isolation inside SAM, researchers are starting to analyze the data he helped generate. The records will reveal not just how one person and a few trays of dwarf peas sustained each other, but how humanity might one day live and breathe beyond Earth.