The search for life on Mars have to go underground, say scientists

The jammed front wheel of NASA’s Spirit rover this trench was dug in Mars’ Gusev Crater in 2008. Spirit’s observations allowed researchers to determine that the white color is evidence of an ancient hydrothermal system on the Red Planet.

(NASA/JPL/Cornell University)

The search for signs of life on Mars must be a bit of a rethink, scientists argue in a new study.

A popular strategy calls for studies into places where the water sediment collected long ago, like the ancient lake-bed environment that NASA’s Curiosity rover discovers Mars’ 96-metre-wide (154 kilometers) Gale Crater.

Here on Earth, such ancient habitats preserve abundant evidence of ancient life — but that does not mean that the same will be true on the Red Planet, according to the study team, which was led by Joseph Michalski, an associate professor in the Department of Earth Sciences at The University of Hong Kong. [The Search for Life on Mars (A Photo Timeline)]

“Mars is not the Earth,” the researchers wrote in the study, a “Perspectives” piece that was published today (Dec. 18) in the journal Nature Geoscience.

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“We must recognize that our whole perspective on how life has evolved, and how the evidence of life is preserved, it is coloured by the fact that we live on a planet where photosynthesis evolved,” they say. “Even if photosynthesis did evolve on Mars, the questions remain as to how successful surface life would have been, and whether the evidence of that life could be recorded in the sedimentary record.”

Life was, for the first time set foot on the Earth about 4 billion years ago, but it really began about 1.5 billion years later, after cyanobacteria evolved oxygen-generating photosynthesis. The oxygen produced by these microbes led to the formation of an atmospheric ozone layer, which protects surface life from harmful ultraviolet radiation.

This evolutionary innovation is therefore opened up vast amounts of livable space, allowing organisms to colonize the surface and near-surface environments on land and at sea, scientists say.

The timing here is important, according to the study team. Mars was once relatively warm and wet —much warmer and wetter than it is now, anyway. But by 4 billion years ago, Mars ‘ interior had cooled enough that the magnetic dynamo shut down, and the Red Planet lost its global magnetic field. (The earth has a magnetic field because our planet is 10 times more mass than Mars, and so are not cooled nearly as much.)

This magnetic field had served to protect the atmosphere of Mars from the solar wind, the stream of charged particles from the sun. The loss resulted in the gutting of this once-thick atmosphere and the transformation of the planet to the cold desert it is today — a process that was largely completed by about 3.7 billion years ago.

Thus, the surface of life to really go and so a good chance to be preserved in lake-bed deposits — photosynthesis probably would have had to evolve at least 1 billion years earlier on Mars than it did on Earth.

Michalski and his colleagues do not think that this is a big bet. So they advocate for the prioritisation of the places where the surface of life may have once teemed on Mars — environments, such as ancient hydrothermal systems, which are life cradle here on Earth.

And you wouldn’t necessarily have to dig deep to find of these systems; NASA’s Spirit rover stumbled on an inside Mars Gusev Crater back in 2008, when the wobbly wheel road scraped some of the surface dirt.

Such reasoning can quickly in real-world applications: In 2020, NASA plans to launch a life-hunting on the Mars rover that will collect and store rock samples for possible return to Earth.

Study co-author Jack Mustard, a professor of geology at Brown University in Rhode Island, said that he’d like the 2020 rover to examine the exposed mineralized fracture zones ” on the Red Planet.

“These are places where there was flow in the crust, and where you will be mixing between the different fluids from different sources may have different concentrations of major elements, as well as the dissolved hydrogen, for example,” said Mustard (Hydrogen is a possible energy source for the microbes.) “That would be cool.”

The main purpose of this study is “to the greater scientific community to think along these lines as we move to continue to search for potential evidence” of life and its precursor molecules, he added.

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