Mars-like places on earth shed light on conditions for life

In even the most inhospitable places -- the freezing Antarctic permafrost, Sun-baked salt pans in Tunisia or the corrosively acidic Rio Tinto in Spain -- pockets of life can be found.

Washington: Researchers from the Centro de Astrobiologia (CAB) in Madrid have made a series of field trips to the most Mars-like places on Earth to better understand the Martian surface and conditions for life.

In even the most inhospitable places -- the freezing Antarctic permafrost, Sun-baked salt pans in Tunisia or the corrosively acidic Rio Tinto in Spain -- pockets of life can be found.

“The big questions are: what is life, how can we define it and what are the requirements for supporting life? To understand the results we receive back from missions like Curiosity, we need to have detailed knowledge of similar environments on Earth,” said Dr. Felipe Gomez, the project leader said.

“Metabolic diversity on Earth is huge. In the field campaigns, we have studied ecosystems in situ and we have also brought samples back to the laboratory for further analysis. We have found a range of complex chemical processes that allow life to survive in unexpected places,” the stated.

Over the past 4 years, the team has carried out field trips to Chott el Jerid, a salt pan in Tunisia, the Atacama desert in Chile, Rio Tinto in Southern Spain and Deception Island in Antarctica.

The data collected from these field campaigns is comparable to the data now being collected by the Remote Meteorological Monitoring Station (REMS) carried by Curiosity, which was built by a team from CAB-INTA.

They also drilled samples to a depth of 3.6 meters in Chott El Jerid and to 6 meters in Atacama. The core samples showed subsurface ecosystems of completely different kinds of bacteria from those found on the surface. The populations of bacteria found at the surface decreased with depth, but there was an increase in archaea, and also single-celled halophilic organisms that are able to oxidize metabolites under aerobic and anaerobic conditions.

“In both Atacama and Chott El Jerid, we found ecosystems at a depth of a few meters that were completely isolated from the surface,” said Gomez.

The surface of Chott El Jerid salt pan is very pure sodium chloride with traces of other salts. The team found small accumulations of organic matter inside the salt crystals. When they analyzed the samples, they found that these were populations of halophilic, salt-loving bacteria that were dormant.

Gomez said, “This was a really exciting find. These condensed accumulations of halophilic bacteria could have been dormant for possibly hundreds of years. Back in the laboratory, we were able to rehydrate the samples and restore the bacteria to life.”

The Mars Exploration Rover, Opportunity, discovered jarosite on the surface of Mars. Jarosite is only synthesized in the presence of water and contains very high concentrations of metals, such as iron.

The team studied outcrops of jarosite at Rio Tinto, areas that have extraordinarily high levels of acidity. Unexpectedly, they found photosynthetic bacteria growing between the layers in salt crusts. When they analyzed the bacteria back in the laboratory, they made a further discovery: that iron appears to protect the bacteria from ultraviolet radiation.

Gomez explained, “We took two samples of the bacteria, one with iron present and one without and exposed them to high levels of ultraviolet radiation. For the sample without iron, nearly all the bacteria were destroyed. For the sample with iron present the population survived. There was a small increase due to toxic super-oxides being created, but the protective effect of ferric compounds was significant.”

Their findings have implications for the development of life on the Earth: early in its formation, the Earth had no oxygen and its atmosphere would not have given the protection from ultraviolet radiation that it provides today.

“What the bacteria we found in Rio Tinto show is that the presence of ferric compounds can actually protect life. This could mean that life formed earlier on Earth than we thought. These effects are also relevant for the formation of life on the surface of Mars,” stated Gomez.

The team also found that salt provides stable conditions that can allow life to survive in very hard environments.

“Within salts, the temperature and humidity are protected from fluctuations and the doses of ultraviolet radiation are very low. In the laboratory, we placed populations of different bacteria between layers of salt a few millimeters thick and exposed them to Martian conditions,” explained Gomez.

“Nearly 100 percent of deinoccocus radiodurans , a hardy type of bacteria, survived being irradiated. But fascinatingly, about 40 percent of acidithiobacillus ferrooxidans -- a very fragile variety of bacteria, also survived when protected by a salt crust,” the researcher added.

They presented their findings during a press conference at the European Planetary Science Congress in Madrid.