Having discovered flowing, liquid water on the once-imagined arid surface of Mars, NASA scientists are looking to the next missing element needed for human habitability on the Red Planet: oxygen.

Finding a way to produce oxygen on the planet is vital if the space agency is to fulfill its goal of sending humans to Mars sometime during the 2030s, they say.

They have considered sending microbes on the journey to fill large bio domes to be built by the astronauts on the planet’s surface. Another idea they’ve pondered is sending along a large machine to split up the oxygen-containing carbon dioxide that makes up most of Mars’ thin atmosphere.

Then there is the Bay Area scientist who has NASA’s ear with his idea that a dangerous salt compound believed to exist on Mars’ surface can be converted into breathable oxygen.

Supporting humans

The compound, a perchlorate, is known to be a threat to human health on Earth, interfering with the production of human growth hormones.

John Coates, a microbiologist at UC Berkeley, has patented a mechanism he says can turn the perchlorate into oxygen fit for humans. Throughout the development process, he consulted NASA scientists who see Coates’ invention as a partial answer to the oxygen issue, but not the entire solution.

“What happens if astronauts are 10 miles from home (base) and they have a big problem and need oxygen? That is the niche that the perchlorate would fill,” said Chris McKay, a planetary scientist at NASA Ames Research Center in Mountain View. “When you are (on Mars) out in middle of nowhere, scooping up a bag of dirt to produce oxygen would be easy to do.”

But Coates said his machine could produce enough oxygen to support human survival on Mars if its surface contains as much perchlorate as some scientists believe — up to 1 percent of the planet’s total surface material.

“As we realize more and more about the water content of Mars, then we realize oxygen is the limiting factor,” Coates said.

His device would extract perchlorate from the Martian surface using water, creating a solution that would then be combined with microorganisms and an electrical charge to produce oxygen. One kilogram of rocky, perchlorate-filled material would provide enough oxygen for 12 minutes of human consumption, he said.

Reusing water

Solar panels would power the machine, and the water it uses would be cycled back into the process for reuse.

“The only thing consumed in the process is the perchlorate,” Coates said.

That’s another benefit NASA sees in Coates’ machine, McKay said.

“A lot of John’s work is and was focused on how to clean up soil and water that is contaminated with perchlorate,” he said. “We may have to think of that on Mars. We would need to have ways to clean it up while astronauts are there. ... It is essentially a giant Superfund site.”

In 2008, after evidence of perchlorate was found on Mars by NASA’s Phoenix lander, McKay and Alfonso Davila from the SETI Institute in Mountain View solicited Coates to lead a conversation about perchlorate’s role in a mission that would take humans to Mars. The scientists met when they could, and even recruited students to help with research, Davila said.

“We kind of set up this perchlorate club,” he said. “We asked: What is the relevance and importance of this? Through conversations we started understanding the implications.”

The scientist ultimately concluded that perchlorate could be a benefit.

“We ran some numbers. and it turns out you don’t need that much soil to produce an amount of oxygen that would be useful,” Davila said.

Trip planned in 2020

Still, McKay said NASA will probably end up settling on one of the options it already had been considering for oxygen production on Mars, and use Coates’ device as a backup.

“We would probably get oxygen from carbon dioxide in the atmosphere,” he said.

He and Davila said NASA is planning a Mars trip in 2020, when it will test a machine to do just that. If all goes well, a similar machine could travel to Mars on the manned mission, they said.

Kevin Schultz is a San Francisco Chronicle staff writer. E-mail: kschultz@sfchronicle.com Twitter: KevinEdSchultz