Ocean Insights to Life on Mars

According to popular culture, extraterrestrial life might look like the iridescent green egg that launched terror in the 1979 movie “Alien,” or fly in sophisticated spaceships to deliver linguistically complex messages as in 2016’s “Arrival.” But if you ask a scientist, the most likely extraterrestrial life looks like the microbes that live in Earth’s deep ocean and subsurface.

“The evolution of life on Earth has been a huge, ongoing biological experiment,” Senior Research Scientist Ramunas Stepanauskas said. “Finding life on Mars would provide a second case of life in the universe and allow us to have a meaningful discussion about what it takes for life to emerge.”

Looking for this life is complicated. It is difficult to know what visual and chemical clues to expect, where to find them, and how to avoid contaminating the research site and samples with microbes from Earth. Several researchers at Bigelow Laboratory are looking for answers to these problems by applying what they’ve learned through ocean research to the search for life on Mars. 

Postdoctoral Researcher Rose Jones and other team members working with Senior Research Scientist Beth Orcutt are wielding chemistry and physics to narrow down what types of microbes could live on Mars. Jones studies microbes that live in “analog environments”— places on Earth that resemble Martian environments and can yield valuable insights about what life could look like there.

“Some really weird microbes live on Earth,” Jones said. “We have microbes that thrive in pools of acid and in hydrothermal vent fluids. Some environments on Mars are probably no more extreme.”

The microbes Jones is interested in thrive in places like the ocean subseafloor, inside the continental crust, buried beneath ice in subglacial lakes, and under polar desert soils. These environments are isolated from the sun, limited in oxygen, and barely influenced by the surface world. By studying the chemistry of these environments and the characteristics of microbes that make a living there, Jones can narrow down what astrobiologists should look for in comparable places on Mars.

Jones and colleagues recently published a study on low-energy analog environments in the journal Frontiers in Microbiology. As future Mars missions bring back more detailed data, Jones will be able to refine her calculations about the possible chemical pathways microbes could use to live on Mars. This research drew on grants from the Center for Dark Energy Biosphere Investigations Science and Technology Center, the NASA Astrobiology Institute Life Underground program, and the Deep Carbon Observatory.

“What we’re doing now would have been considered science fiction even 20 years ago,” Jones said. “It boggles the mind that similar organisms could live on Mars and Earth.”

Senior Research Scientist Dave Emerson is also developing new ways to search for life on Mars. He is an expert on iron-oxidizing bacteria, microorganisms that process iron for energy.

“Iron-oxidizing bacteria are ancient microbes, and they thrive in environments as common as roadside ditches and as extreme as deep-sea hydrothermal vents,” Emerson said. “I think they could live on Mars as well. After all, it’s called the 'red planet’ because its rocks are so rich in rust.”

Iron-oxidizing bacteria generate energy by transferring electrons between iron and oxygen. This process produces rust minerals as byproducts, which the microbes often convert to ribbon-like structures as they grow. These twisted stalks are visually distinctive and can become fossilized, making them an effective biosignature that provides evidence of past or present life. 

Leveraging funding from the NASA Exobiology program, Emerson and colleagues at NASA’s Goddard Space Flight Center recently discovered an organic molecule that seems unique to iron-oxidizing bacteria and can be preserved in rocks under the right conditions. This biosignature could provide another way to identify iron-powered life on Mars. Emerson and his NASA colleagues recently published a paper announcing this discovery in the journal Astrobiology.

“These are molecules we wouldn’t expect to be formed any way other than by life,” Emerson said. “Using this biosignature could be transformational for our understanding of both Mars and ancient Earth.” 

If microbes are found on Mars, it will be essential to know whether they indeed originated there or traveled to the planet aboard NASA’s spacecraft. Success of the mission will depend on rover cleanliness and a thorough understanding of the microbes that might make the journey. Stepanauskas is collaborating with NASA’s Jet Propulsion Laboratory to help minimize the risk of microbial contamination for the Mars mission that launches in 2020, which has a key goal of searching for microbial life. Stepanauskas directs the Single Cell Genomics Center at Bigelow Laboratory, where he uses novel techniques to detect and genetically sequence individual cells. 

“If microbes are really rare in Martian samples, it won’t be simple to identify life that is actually from Mars, rather than contamination from Earth,” Stepanauskas said. “Any doubt about the origin of the microbes would be detrimental to the science and very costly, so we must maximize the chances of clean results.”

Protecting the planet will also be essential during the mission. Remote sensing suggests that Mars has slopes covered by flowing liquid in the summertime, which may be hospitable to life. NASA currently avoids the places it believes are most suitable for microbial life, for fear that spacecraft could contaminate them with microbes from Earth. The work done in the Single Cell Genomics Center will feed into the decision-making process on selecting sites for the Mars rover to explore.

“This is a good example of how technology we developed from marine microbiology finds use in diverse applications as exotic as the search for life on other planets,” Stepanauskas said. “Microbes have thrived in the ocean for nearly a third of the age of the universe. Finding them on Mars as well would put in perspective what is so special about ocean microbes.”

Upper image courtesy of NASA/JPL-Caltech. Lower image courtesy of Ocean Exploration Trust and NASA SUBSEA Expedition.