Mars has right ingredients for present-day microbial life beneath its surface, study finds

As NASA's Perseverance rover begins its search for ancient life on the surface of Mars, a new study suggests that the Martian subsurface might be a good place to look for possible present-day life on the Red Planet.

The study, published in the journal Astrobiology, looked at the chemical composition of Martian meteorites -- rocks blasted off of the surface of Mars that eventually landed on Earth. The analysis determined that those rocks, if in consistent contact with water, would produce the chemical energy needed to support microbial communities similar to those that survive in the unlit depths of the Earth. Because these meteorites may be representative of vast swaths of the Martian crust, the findings suggest that much of the Mars subsurface could be habitable.

"The big implication here for subsurface exploration science is that wherever you have groundwater on Mars, there's a good chance that you have enough chemical energy to support subsurface microbial life," said Jesse Tarnas, a postdoctoral researcher at NASA's Jet Propulsion Laboratory who led the study while completing his Ph.D. at Brown University. "We don't know whether life ever got started beneath the surface of Mars, but if it did, we think there would be ample energy there to sustain it right up to today."

In recent decades, scientists have discovered that Earth's depths are home to a vast biome that exists largely separated from the world above. Lacking sunlight, these creatures survive using the byproducts of chemical reactions produced when rocks come into contact with water.

One of those reactions is radiolysis, which occurs when radioactive elements within rocks react with water trapped in pore and fracture space. The reaction breaks water molecules into their constituent elements, hydrogen and oxygen. The liberated hydrogen is dissolved in the remaining groundwater, while minerals like pyrite (fool's gold) soak up free oxygen to form sulfate minerals. Microbes can ingest the dissolved hydrogen as fuel and use the oxygen preserved in the sulfates to "burn" that fuel.

In places like Canada's Kidd Creek Mine, these "sulfate-reducing" microbes have been found living more than a mile underground, in water that hasn't seen the light of day in more than a billion years. Tarnas has been working with a team co-led by Brown University professor Jack Mustard and Professor Barbara Sherwood Lollar of the University of Toronto to better understand these underground systems, with an eye toward looking for similar habitats on Mars and elsewhere in the solar system. The project, called Earth 4-D: Subsurface Science and Exploration, is supported by the Canadian Institute for Advances Research.

For this new study, the researchers wanted to see if the ingredients for radiolysis-driven habitats could exist on Mars. They drew on data from NASA's Curiosity rover and other orbiting spacecraft, as well as compositional data from a suite of Martian meteorites, which are representative of different parts of the planet's crust.

The researchers were looking for the ingredients for radiolysis: radioactive elements like thorium, uranium and potassium; sulfide minerals that could be converted to sulfate; and rock units with adequate pore space to trap water. The study found that in several different types of Martian meteorites, all the ingredients are present in adequate abundances to support Earth-like habitats. This was particularly true for regolith breccias -- meteorites sourced from crustal rocks more than 3.6 billion years old -- which were found to have the highest potential for life support. Unlike Earth, Mars lacks a plate tectonics system that constantly recycle crustal rocks. So these ancient terrains remain largely undisturbed.

The researchers say the findings help make the case for an exploration program that looks for signs of present-day life in the Martian subsurface. Prior research has found evidence of an active groundwater system on Mars in the past, the researchers say, and there's reason to believe that groundwater exists today. One recent study, for example, raised the possibility of an underground lake lurking under the planet's southern ice cap. This new research suggests that wherever there's groundwater, there's energy for life.

Tarnas and Mustard say that while there are certainly technical challenges involved in subsurface exploration, they aren't as insurmountable as people may think. A drilling operation wouldn't require "a Texas-sized oil rig," Mustard said, and recent advances in small drill probes could soon put the Martian depths within reach.

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Preconditions for life present 3.5 billion years ago

Microbial life already had the necessary conditions to exist on our planet 3.5 billion years ago. This was the conclusion reached by a research team after studying microscopic fluid inclusions in barium sulfate (barite) from the Dresser Mine in Marble Bar, Australia. In their publication "Ingredients for microbial life preserved in 3.5-billion-year-old fluid inclusions," the researchers suggest that organic carbon compounds which could serve as nutrients for microbial life already existed at this time. The study by first author Helge Mißbach (University of Göttingen, Germany) was published in the journal Nature Communications. Co-author Volker Lüders from the GFZ German Research Center for Geosciences carried out carbon isotope analyses on gases in fluid inclusions.

Fluid inclusions show potential for prehistoric life

Lüders assesses the results as surprising, although he cautions against misinterpreting them. "One should not take the study results as direct evidence for early life," says the GFZ researcher. Rather, the findings on the 3.5-billion-year-old fluids showed the existence of the potential for just such prehistoric life. Whether life actually arose from it at that time cannot be determined. Based on the results, "we now know a point in time from which we can say it would have been possible," explains Lüders.

Australian barites as geo-archives

Fluid inclusions in minerals are microscopic geo-archives for the migration of hot solutions and gases in the Earth's crust. Primary fluid inclusions were formed directly during mineral growth and provide important information about the conditions under which they were formed. This includes the pressure, temperature and the solution composition. In addition to an aqueous phase, fluid inclusions can also contain gases whose chemistry can persist for billions of years. The fluid inclusions examined in this study were trapped during crystallization of the host minerals. The fluid inclusions investigated in this study originate from the Dresser Mine in Australia. They were trapped during crystallisation of the host minerals of barium sulphate (barite). The research team analysed them extensively for their formation conditions, biosignatures and carbon isotopes.

In the course of the analyses, it turned out that they contained primordial metabolism -- and thus energy sources for life. The results of Lüders' carbon isotope analysis provided additional evidence for different carbon sources. While the gas-rich inclusions of gray barites contained traces of magmatic carbon, clear evidence of an organic origin of the carbon could be found in the fluid inclusions of black barites.

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Touchdown! NASA's Mars Perseverance rover safely lands on Red Planet

 The largest, most advanced rover NASA has sent to another world touched down on Mars Thursday, after a 203-day journey traversing 293 million miles (472 million kilometers). Confirmation of the successful touchdown was announced in mission control at NASA's Jet Propulsion Laboratory in Southern California at 3:55 p.m. EST (12:55 p.m. PST).

Packed with groundbreaking technology, the Mars 2020 mission launched July 30, 2020, from Cape Canaveral Space Force Station in Florida. The Perseverance rover mission marks an ambitious first step in the effort to collect Mars samples and return them to Earth.

"This landing is one of those pivotal moments for NASA, the United States, and space exploration globally -- when we know we are on the cusp of discovery and sharpening our pencils, so to speak, to rewrite the textbooks," said acting NASA Administrator Steve Jurczyk. "The Mars 2020 Perseverance mission embodies our nation's spirit of persevering even in the most challenging of situations, inspiring, and advancing science and exploration. The mission itself personifies the human ideal of persevering toward the future and will help us prepare for human exploration of the Red Planet."

About the size of a car, the 2,263-pound (1,026-kilogram) robotic geologist and astrobiologist will undergo several weeks of testing before it begins its two-year science investigation of Mars' Jezero Crater. While the rover will investigate the rock and sediment of Jezero's ancient lakebed and river delta to characterize the region's geology and past climate, a fundamental part of its mission is astrobiology, including the search for signs of ancient microbial life. To that end, the Mars Sample Return campaign, being planned by NASA and ESA (European Space Agency), will allow scientists on Earth to study samples collected by Perseverance to search for definitive signs of past life using instruments too large and complex to send to the Red Planet.

"Because of today's exciting events, the first pristine samples from carefully documented locations on another planet are another step closer to being returned to Earth," said Thomas Zurbuchen, associate administrator for science at NASA. "Perseverance is the first step in bringing back rock and regolith from Mars. We don't know what these pristine samples from Mars will tell us. But what they could tell us is monumental -- including that life might have once existed beyond Earth."

Some 28 miles (45 kilometers) wide, Jezero Crater sits on the western edge of Isidis Planitia, a giant impact basin just north of the Martian equator. Scientists have determined that 3.5 billion years ago the crater had its own river delta and was filled with water.

The power system that provides electricity and heat for Perseverance through its exploration of Jezero Crater is a Multi-Mission Radioisotope Thermoelectric Generator, or MMRTG. The U.S. Department of Energy (DOE) provided it to NASA through an ongoing partnership to develop power systems for civil space applications.

Equipped with seven primary science instruments, the most cameras ever sent to Mars, and its exquisitely complex sample caching system -- the first of its kind sent into space -- Perseverance will scour the Jezero region for fossilized remains of ancient microscopic Martian life, taking samples along the way.

"Perseverance is the most sophisticated robotic geologist ever made, but verifying that microscopic life once existed carries an enormous burden of proof," said Lori Glaze, director of NASA's Planetary Science Division. "While we'll learn a lot with the great instruments we have aboard the rover, it may very well require the far more capable laboratories and instruments back here on Earth to tell us whether our samples carry evidence that Mars once harbored life."

Paving the Way for Human Missions

"Landing on Mars is always an incredibly difficult task and we are proud to continue building on our past success," said JPL Director Michael Watkins. "But, while Perseverance advances that success, this rover is also blazing its own path and daring new challenges in the surface mission. We built the rover not just to land but to find and collect the best scientific samples for return to Earth, and its incredibly complex sampling system and autonomy not only enable that mission, they set the stage for future robotic and crewed missions."

The Mars Entry, Descent, and Landing Instrumentation 2 (MEDLI2) sensor suite collected data about Mars' atmosphere during entry, and the Terrain-Relative Navigation system autonomously guided the spacecraft during final descent. The data from both are expected to help future human missions land on other worlds more safely and with larger payloads.

On the surface of Mars, Perseverance's science instruments will have an opportunity to scientifically shine. Mastcam-Z is a pair of zoomable science cameras on Perseverance's remote sensing mast, or head, that creates high-resolution, color 3D panoramas of the Martian landscape. Also located on the mast, the SuperCam uses a pulsed laser to study the chemistry of rocks and sediment and has its own microphone to help scientists better understand the property of the rocks, including their hardness.

Located on a turret at the end of the rover's robotic arm, the Planetary Instrument for X-ray Lithochemistry (PIXL) and the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) instruments will work together to collect data on Mars' geology close-up. PIXL will use an X-ray beam and suite of sensors to delve into a rock's elemental chemistry. SHERLOC's ultraviolet laser and spectrometer, along with its Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) imager, will study rock surfaces, mapping out the presence of certain minerals and organic molecules, which are the carbon-based building blocks of life on Earth.

The rover chassis is home to three science instruments, as well. The Radar Imager for Mars' Subsurface Experiment (RIMFAX) is the first ground-penetrating radar on the surface of Mars and will be used to determine how different layers of the Martian surface formed over time. The data could help pave the way for future sensors that hunt for subsurface water ice deposits.

Also with an eye on future Red Planet explorations, the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) technology demonstration will attempt to manufacture oxygen out of thin air -- the Red Planet's tenuous and mostly carbon dioxide atmosphere. The rover's Mars Environmental Dynamics Analyzer (MEDA) instrument, which has sensors on the mast and chassis, will provide key information about present-day Mars weather, climate, and dust.

Currently attached to the belly of Perseverance, the diminutive Ingenuity Mars Helicopter is a technology demonstration that will attempt the first powered, controlled flight on another planet.

Project engineers and scientists will now put Perseverance through its paces, testing every instrument, subsystem, and subroutine over the next month or two. Only then will they deploy the helicopter to the surface for the flight test phase. If successful, Ingenuity could add an aerial dimension to exploration of the Red Planet in which such helicopters serve as a scouts or make deliveries for future astronauts away from their base.

Once Ingenuity's test flights are complete, the rover's search for evidence of ancient microbial life will begin in earnest.

"Perseverance is more than a rover, and more than this amazing collection of men and women that built it and got us here," said John McNamee, project manager of the Mars 2020 Perseverance rover mission at JPL. "It is even more than the 10.9 million people who signed up to be part of our mission. This mission is about what humans can achieve when they persevere. We made it this far. Now, watch us go."

More About the Mission

A primary objective for Perseverance's mission on Mars is astrobiology research, including the search for signs of ancient microbial life. The rover will characterize the planet's geology and past climate and be the first mission to collect and cache Martian rock and regolith, paving the way for human exploration of the Red Planet.

Subsequent NASA missions, in cooperation with ESA, will send spacecraft to Mars to collect these cached samples from the surface and return them to Earth for in-depth analysis.

The Mars 2020 Perseverance mission is part of NASA's Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.

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