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If humans are ever going to live beyond Earth, they'll need to construct habitats. But transporting enough industrial material to create livable spaces would be incredibly challenging and expensive. Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) think there's a better way, through biology.

An international team of researchers led by Robin Wordsworth, the Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences, have demonstrated that they can grow green algae inside shelters made out of bioplastics in Mars-like conditions. The experiments are a first step toward designing sustainable habitats in space that won't require bringing materials from Earth.

"If you have a habitat that is composed of bioplastic, and it grows algae within it, that algae could produce more bioplastic," explained Wordsworth. "So you start to have a closed-loop system that can sustain itself and even grow through time."

The research is in Science Advances.

Growing algae in Mars-like conditions

In lab experiments that recreated the thin atmosphere of Mars, Wordsworth's team grew a common type of green algae called Dunaliella tertiolecta. The algae thrived inside a 3D-printed growth chamber made from a bioplastic called polylactic acid, which was able to block UV radiation while transmitting enough light to allow the algae to photosynthesize.

The algae was kept under a Mars-like 600 Pascals of atmospheric pressure—over 100 times lower than Earth—and in a carbon dioxide-rich environment, as opposed to mostly nitrogen and oxygen like on Earth.

Liquid water cannot exist at such low pressures, but the bioplastic chamber created a pressure gradient that stabilized water within it. The experiments point to bioplastics as potentially key to creating renewable systems for maintaining life in a lifeless environment.

The concept the researchers demonstrated is closer to how organisms grow naturally on Earth, and it contrasts with an industrial approach using materials that are costly to manufacture and recycle.

Humans living in space

Wordsworth's team previously demonstrated a type of local Martian terraforming using sheets of silica aerogels that mimic Earth's greenhouse warming effect to allow for biological growth.

A combination of the algae experiments with the aerogels would solve both temperature and pressure issues for supporting plant and algae growth, Wordsworth said, and could open a clearer path toward extraterrestrial existence.

Next, Wordsworth said the researchers want to demonstrate that their habitats also work in vacuum conditions, which would be relevant for lunar or deep-space applications. His team also has plans to design a working closed-loop system for habitat production.

"The concept of biomaterial habitats is fundamentally interesting and can support humans living in space," Wordsworth said.

"As this type of technology develops, it's going to have spin-off benefits for sustainability technology here on Earth as well."