Building Blocks of Life Found on Mars

Two landmark discoveries reveal organic carbon on the red planet, shaping the future hunt for life on Mars.

NASA's Curiosity rover drilled this two-inch-deep hole in a Martian rock as part of its examinations of the red planet's soil composition.

MARS returns for a second season this fall on National Geographic.

Day to day, it’s easy to lose sight of an astonishing fact: Since 2012, humankind has been driving a nuclear-powered sciencemobile the size of an SUV on another planet.

This engineering marvel, NASA’s Mars rover Curiosity, has revolutionized our understanding of the red planet. And thanks to the intrepid rover, we now know that ancient Mars had carbon-based compounds called organic molecules—key raw materials for life as we know it.

A new study published in Science on Thursday presents the first conclusive evidence for large organic molecules on the surface of Mars, a pursuit that began with NASA’s Viking landers in the 1970s. Earlier testsmay have hinted at organics, but the presence of chlorine in martian dirt complicated those interpretations.

“When you work with something as crazy as a rover on Mars, with the most complex instrument ever sent to space, it seems like we’re doing what may have been perceived earlier as impossible,” says lead author Jennifer Eigenbrode, a biogeochemist at NASA Goddard. “I work with an amazing group of people on Mars, and we have discovered so much.”

Mars 101

Curiosity's latest data reveal that the watery lake that once filled Mars’s Gale Crater contained complex organic molecules about 3.5 billion years ago. Hints of them are still preserved in sulfur-spiked rocks derived from lake sediments. Sulfur may have helped protect the organics even when the rocks were exposed at the surface to radiation and bleach-like substances called perchlorates.

By themselves, the new results aren't evidence for ancient life on Mars; non-living processes could have yielded identical molecules. At a minimum, the study shows how traces of bygone martians could have survived for eons—if they existed at all—and it hints at where future rovers might look for them.

“This is an important finding,” says Samuel Kounaves, a Tufts University chemist and former lead scientist for NASA's Phoenix Mars lander. “There are locations, especially subsurface, where organic molecules are well-preserved.”

Seasons of Methane

In addition to ancient carbon, Curiosity has caught whiffs of organics that exist on Mars today. The rover has periodically sniffed Mars’s atmosphere since it landed, and in late 2014, researchers using these data showed that methane—the simplest organic molecule—is present in Mars’s atmosphere.

Methane’s presence on Mars is puzzling, because it survives only a few hundred years at a time, which means that somehow, something on the red planet keeps replenishing it. “It’s a gas in the atmosphere of Mars that really shouldn’t be there," says NASA Jet Propulsion Lab scientist Chris Webster.

A self portrait of the Mars rover Curiosity.

This field of dunes lies on the floor of an old crater in Noachis Terra, one of the oldest places on Mars.

This enhanced color image shows several craters somewhere in the southern mid-latitudes of Mars. The bluish deposits are most likely iron-bearing minerals that have not been previously oxidized, or rusted.

The impact site of the heat shield from NASA's Mars Exploration Rover Opportunity.

Sand dunes are among the most widespread aeolian, or wind-blown, features on Mars. These areas provide clues to the sedimentary history of the surrounding terrain.

Groups of dark brown streaks were photographed by the Mars Reconnaissance Oriber on melting pinkish sand dunes covered with light frost.

The panoramic camera on NASA's Mars Exploration Rover Opportunity caputured this scene of the west rim of Endeavour Crater during the summer of 2014.

Sand dunes litter the floor of Aram Chaos, an eroded impact crater east of Mars' Valles Marineris canyon range.

Melas Chasma is the widest segment of Valles Marineris, the largest canyon in the solar system.

The Opportunity rover spent four months perched on the northern slope of Greely Haven and snapped more than 800 images of its surroundings.

Russell Crater dunes are a favorite target for the Mars Reconnaissance Orbiter's HiRISE camera, not only because of their incredible beauty, but for measuring the accumulation of frost each fall and its disappearance in the spring.

The holes visible in this image are not impact craters, but rather material that was ejected from a large crater called Hale that does not appear in here. Explosions formed moats, which have been partially covered over time by sand dunes (top).

NASA's Curiosity rover snapped this 360-degree panorama as part of a long-term campaign to document the context and details of the geology and landforms along Curiosity's traverse since landing in 2012.

Recurring slope linae (RSL) are seasonal flows on warm slopes, and are especially common in central and eastern Valles Marineris.

Victoria Crater has a distinctive "scalloped" shape to its rim, caused by erosion and downhill movement of crater wall material.

Dust accumulation on a rover's solar panels reduces its power supply, and the rover's mobility is limited until winter is over or wind cleans the panels.

The Curiosity rover captured the Bagnold Dunes inside Gale Crater on Sept. 25, 2015.

Partially exposed bedrock is exposed within the Koval'sky impact basin.

This dramatic, fresh impact crater spans approximately 100 feet (30 meters) in diameter and is surrounded by a large, rayed blast zone.

The north polar layered deposits are layers of dusty ice up to three kilometers (two miles) thick and approximately 1,000 kilometers (620 miles) in diameter.

Sand dunes are among the most widespread wind-formed features on Mars. Their distribution and shapes are affected by changes in wind direction and wind strength.

This selfie from NASA's Curiosity rover shows the vehice at the site from which it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp.

Researchers used the Curiosity rover in March 2015 to examine the structure and composition of the crisscrossing veins at the "Garden City" site in the center of this scene.

This crater near Sirenum Fossae has steep inner slopes carved by gullies.

This image covers many shallow irregular pits with raised rims, but researchers aren't sure how these odd features formed.

At this site in the lower mounter in Gale Crater, orbiting instruments have detected signatures of both clay minerals and sulfate salts. This change in mineralogy may reflect a change in the ancient environment in Gale Crater.

Viscous, lobate flow features are commonly found at the bases of slopes in the mid-latitudes of Mars, and are often associated with gullies.

Many Martian landscapes contain features that are familiar to ones we find in Earth, like river valleys, cliffs, glaciers and volcanoes.

Two of the raised treads, called grousers, on the left middle wheel of NASA's Curiosity rover broke during the first quarter of 2017, including the one seen partially detached at the top of the wheel in this image from the camera on the rover's arm.

In the scenic "Murray Buttes" area, individual buttes and mesas were assigned numbers. This one is referred to as "M9a."

This observation from NASA's Mars Reconnaissance Orbiter shows late summer in Mars' southern hemisphere. The sun is low in the sky, highlighting the subtle topography.

NASA's Curiosity rover team has assessed the small bright object just below the center of this image and believe it is debris from the spacecraft.

The "High Dune", which is part of the "Bagnold Dunes," was the first Martian sand dune ever studied up close. The dunes are active, migrating up to about one yard or meter per year.

A towering dust devil casts a serpentine shadow over the Martian surface in this stunning, late springtime image of Amazonis Planitia.

Landforms called "gullies" found on many large Martian sand dunes consist of an alcove, channel, and apron.

NASA plans to launch a rover to Mars in both 2018 and in 2020.

Tap images for captions

In addition, methane's observed behavior on Mars is bizarre. In 2009, researchers reported that inexplicable martian plumes randomly belch out thousands of tons of methane at a time.

Webster’s latest study, also published today in Science, shows that Mars seasonally “breathes” the stuff. Each martian summer, the atmosphere’s methane concentration rises to about 0.6 parts per billion. In the winter, this count ebbs by a factor of three to 0.2 parts per billion.

“We don’t have seasonal variations in many molecules in Earth’s atmosphere, so to have a planet have seasonal variations in chemistry is very otherworldly,” says Eigenbrode. “It’s an astounding observation.”

Webster and his colleagues suspect that the methane comes from deep underground, and temperature swings on Mars’s surface throttle its flow upward. In the winter, the gas could get trapped underground in icy crystals called clathrates, which may melt in the summer and free the gas.

But what’s making the methane? Nobody knows.

“We really can’t tell if this methane we see today is a current product of serpentinization [a chemical reaction between iron-bearing rocks and liquid water] or microbial activity at some depth,” says Michael Mumma, the NASA Goddard scientist who discovered Mars’s methane plumes. “Or is it something that is stored from an ancient time that’s being slowly released?”

Still Looking for Life

Experts have hailed the two new studies as milestones for astrobiology.

“It’s incredibly exciting, because it shows that Mars is an active planet today,” says Caltech planetary scientist Bethany Ehlmann, a Mars expert who wasn’t involved with the studies. “It’s not cold and dead—it’s perhaps hovering right on the edge of habitability.”

Rocks line an ancient channel where water may have once flowed on Mars.

But Webster and others stress that the studies themselves aren't evidence for life on Mars: “The observations we see do not rule out the possibility of biological activity, [but] it’s not a smoking gun for it.”

To get firmer answers, researchers will need to get equipment to Mars that’s sensitive enough to detect life’s thumb on the chemical scales. On Earth, life makes more methane and less of the gas ethane than non-living reactions do. If researchers saw this signature on Mars, the case for life would get stronger.

Future missions will help. The European Space Agency's ExoMars spacecraft, due to land in 2020, will be able to drill more than six feet down into pristine martian soils and examine samples with its on-board suite of instruments. And NASA’s scheduled Mars 2020 rover is slated to package soil samples for future missions to pick up and return to Earth.

Even now, the ExoMars mission is making strides. The mission's Trace Gas Orbiter arrived at Mars in late 2016, and it’s currently collecting data that will let scientists map Mars’s methane—and maybe even pinpoint its sources.

“We just a few weeks ago started our measurements in the most sensitive mode, and the teams are working hard on extracting the data on methane,” Håkan Svedhem, the project scientist for the Trace Gas Orbiter, says in an email. “We believe we will be able to present results on this in a few weeks’ time.” 

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