NASA's push to land humans on the moon in 2024, along with the agency's ongoing research on the International Space Station (ISS), could serve as excellent analog environments for a mission to Mars, several researchers said at the Humans to Mars Summit in Washington on Thursday (May 16).

A group of researchers from space agencies, private spaceflight companies and other organizations around the world discussed how to best prepare for a mission to Mars. Such a venture involves several additional risks compared to an excursion to the moon. Among those risks, humans on Mars will have to spend long periods of time on the planet's surface in an environment that could contain Martian microbes.

Already, research on the ISS has helped NASA make plans to mitigate some of the risks of sending humans to Mars, said Julie Robinson, who is chief scientist of the orbiting complex at NASA's Johnson Space Center in Houston. For example, researchers have spent the better part of 20 years investigating the effects of microgravity on the human body; these include weakened muscles and bones, fluid shifts, and cardiovascular deconditioning.

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There is less risk of some of those health issues today, however, due to research on the ISS, Robinson said. We know more about how microgravity affects the human body now than we did before the ISS launched more than 20 years ago. But Mars remains tough. "As we look at the risks for all the design reference missions that could be done ... the most significant would be a human mission to Mars," she said.

Robinson added that NASA's plan to land humans on the moon would provide useful data for ISS missions, which take place fully in microgravity. Watching people adapt to gravity in the lunar environment, where they weigh one-sixth as much as they do on Earth, provides an idea of how to get ready for working on Mars. A slightly larger world than the moon, Mars has a gravity that's approximately 38% of Earth's.

Robinson's mention of lunar and ISS analogs for a human mission to Mars was also taken up by a representative from the German Aerospace Center (DLR) and another from Duke University, although their talks (which are discussed below) focused on other topics.

Martian life could be a threat

The big unknown on Mars is the possible presence of life, said Lisa Pratt, NASA's planetary protection officer. Her job is to lead a team to reduce the risks of Earth equipment contaminating the surface of Mars and to prevent nasty Martian microbes from being transferred back to our own planet during future sample-return missions.

Bringing samples back from a location like Mars is science fiction right now, but the future "is closer than you think," Pratt said. NASA's plans call for the first sample-return mission as early as 2026, which gives the agency only about five years to develop the appropriate technology before it gets finalized for flight. And the Mars 2020 rover mission, which launches next year, will cache samples for that 2026 sample-return mission.

Much of our uncertainty about Martian life arises because we don't know what lies underground on the Red Planet, Pratt said. "There is uncertainty about vapor caves or saline groundwater below the surface of Mars," she said. Certain bacteria can thrive in high-salt environments, for example. And salts allow liquid water to flow at more-frigid temperatures that are consistent with what is found at the surface of Mars.

Pratt also worried about Earth organisms contaminating the Martian environment . While studies are ongoing, "we don't know who is there," she said of the microorganisms on spacecraft. "We don't know much about the ecology of organisms that can survive in a clean-room assembly process and get on a spacecraft and launch."

While the transit in space between Earth and Mars, an environment with high radiation and no oxygen, could kill some organisms, it's unclear how many would survive, she added.

Studies on the ground

While space environments offer better analogs for studying how the human body will behave during a Mars mission, ongoing studies on the ground here on Earth are also important to help researchers understand the risks humans face. Radiation, microbiology, waste management, and human health and performance are the four main areas under study by DLR, said Ruth Hemmersbach. She's that agency's head of the division of gravitational biology and the vice director of the agency's Institute of Aerospace Medicine.

"I think it's not only necessary to do experiments in space, but we have to do these possibilities on the ground in possible microgravity environments," she said. One example is a unique DLR test facility called Envihab; it uses " bed rest studies ," in which patients remain in bed for months at a time to see how their body changes. In this controlled environment, it's easy to change parameters such as light and atmospheric conditions and watch how people react. One active area of study looks at changes in vision , which astronauts on the ISS already experience.

Astronaut crews today tend to be made up of superhealthy people who are not necessarily representative of the human population as a whole, noted Daniel Buckland; he works at Duke University as an assistant professor of both emergency medicine and mechanical engineering. He urged space agencies to consider countermeasures to allow more-ordinary humans to participate.

"It would be a tremendous waste of potential if the best botanist or geologist can't go [to Mars] because they are diabetic," Buckland said. "The current model of space medicine is [to] take the healthiest people you can. It limits the kind of people that can go and do the experiments on the surface."

More study is ongoing into sex-based health care, including how different sexes react to the stresses of spaceflight, said Saralyn Mark, an endocrinologist, geriatrician and women's health specialist who used to be a senior medical advisor at NASA, among other prominent positions. She is now president of iGIANT, a nonprofit that focuses on translating research into gender- and sex-specific elements.

Mark said that the decadal reviews used the definitions provided by the Institute of Medicine to define sex and gender: namely, sex is the biological construct whereas gender is the psychosocial construct. The definition is more nuanced today due to the influence of epigenetics, or changes in gene expression. She emphasized that there should not be a "battle of the sexes," but a focus on developing countermeasures and protocols to ensure that men and women can live and perform their duties safely and well during space exploration.

All sessions for the 2019 Humans to Mars summit will be archived on the organization's website .

Editor's Note: This article was corrected to remove an erroneous sentence about visual disturbances in space in men versus women and to clarify Mark's remarks about the definitions of sex and gender.