Are we alone? The search for life on Mars and elsewhere in the solar system

NASAFind life on MarsDriven by the chariot of perseverance, it is likely to yield promising results soon. Previous endeavors, while not definitively demonstrating life, have informed current investigation techniques and expanded our understanding of non-biological processes that can mimic life, bolstering future exploration of habitable spaces across the solar system, including icy moons. Saturn And Jupiter.

While Mars appears to be a promising nearby place to search for life beyond Earth, the Red Planet has stubbornly held on to its secrets. Despite decades of investigation – and even two initially sensational findings – no sure signs of life have yet emerged.

Now that long search could be about to bear fruit. The Perseverance rover has been scouring an ancient Martian crater, which was filled with water, looking for evidence of past life, storing samples of rocks and surface material in metal tubes for eventual return to Earth.

And these exciting past findings, though now considered to fail to prove that life flourished on our neighboring planet, are seen as an essential foundation for the focused, multilayered research being conducted today.

“Past missions have helped us better understand how to search for life,” said Lindsey Hayes, deputy program scientist in the Astrobiology Program — which studies the possibility of life beyond Earth — at NASA Headquarters in Washington, and deputy principal scientist for the Mars sample. return mission.

An in-depth exploration of Mars will also serve as a proving ground for the broader research to come: scanning the ice-covered moons of the outer solar system for some signs of life in the vast oceans hidden beneath their surfaces.

“NASA has invested a lot in the search for life on Mars, and I’ve learned a lot that will help us when we look at other habitable places in the solar system — such as the icy moons orbiting Saturn and Jupiter,” said Marie Vojtek, director of the NASA Astrobiology Program at NASA. Agency headquarters in Washington.

Jezero Crater on Mars is shown in this illustration as it looked billions of years ago, when it was a crater lake with a river delta. Source: NASA/JPL-Caltech/Lizbeth B. De La Torre

Searching for Martian rocks

To find the roots of NASA’s strategy of searching for life among our neighboring worlds, we might look back to the 1970s: the days of Carl Sagan and his two Viking landers, which made history when they both landed on Mars in 1976.

Sagan, host of the original TV series “Cosmos,” helped design and manage Viking 1 and Viking 2, which transmit imagery and collect scientific data from the surface of Mars. They also conducted life-detection experiments, collected samples of the Martian surface material, called regolith, and added nutrients. Despite evidence of consumption of some nutrients, most of the scientific community has concluded that this is likely due to non-biological interactions, which led to an initial spark of excitement over the possible discovery of life on Mars.

The second big moment came in 1996, when NASA scientists published a paper outlining possible chemical traces of life forms in a Martian rock that fell to Earth. Colloquially known as the Allan Hills meteorite, or by its official number, ALH84001, it was collected in Antarctica more than a decade ago.

While meteorites from Mars have fallen to Earth regularly over the history of the two planets — likely blasted off into space when large bodies like asteroids slammed into the Red Planet, and eventually captured by Earth’s gravitational field — this one seemed special. It contained chemical traces similar to those left behind by Earth’s microbes. Some of the images even revealed microscopic, bacteria-like features. Once again, however, global excitement for the potential discovery has been reduced to uncertainty. Today, most scientists who have studied this question consider a non-biological source to be the likely origin of the “evidence” of traces of earlier Martian microbes in the meteorite.

The group of researchers who published the paper, led by NASA scientist David S. McKay, “were at times kind of a bit of a short change,” said Andrew Steele, a researcher at the Carnegie Institution who also investigated the Martian rock. “The actual impact they’ve had on this science should be celebrated, because they took chances that they did. That’s what made us able to ask the next set of really important questions.”

The team’s findings spurred further research and highlighted a new realization: Many non-biological processes can produce realistic features.

Source: NASA/JPL-Caltech/Lizbeth B. De La Torre

Steele’s own work, for example, aims to establish the background level of “lack of life” for environments found on other worlds, including Mars. The results of detecting potential life can then be measured against this background. Building on the work of Mackay’s group and others, Steele and colleagues have found three separate chemical processes that could produce the building blocks of life on Mars — each making organic molecules in the absence of any biological activity.

“Mars is exciting,” he said, “and may still be showing signs of life.” “But it also teaches us how the building blocks of life can form.”

Those two early attempts to find Martian life also led to another key finding: The search needed to be exhaustive, not “grab and go,” as the astrobiologist Hayes puts it.

“Both interpretations of the findings have been hampered by a lack of context,” Hayes said. “In the case of the Vikings, there was a lack of context in the measurements they were about to make – and what they could tell us about the environment in which we were measuring them. In the case of the Allan Hills [the Martian meteorite]Having no context about the environment those rocks came from.”

The search for life on Mars

To move the investigation forward, NASA first decided not to take a direct aim at discovering life itself. Instead, the twin rover Spirit and Opportunity conducted a detailed survey of the Martian environment, confirming the habitable conditions of early Mars in part through geological evidence of water flow. Martian orbiters such as the Mars Reconnaissance Orbiter and Mars Odyssey have also played a role, helping to map terrain and locate landing sites.

The Mars Curiosity rover has pushed the habitability potential even further, capturing evidence of abundant water, organic molecules, and habitable environments in Mars’ distant past. The rover continues its operation today at Gale Crater, where it can still find evidence of past water activity.

NASA is back in the field of life detection with the arrival of the rover at Jezero Crater in February 2021. Once a lake complete with a river delta, Jezero seemed an ideal place to search for signs of life from Mars’ distant past.

But unlike the Viking landers, Perseverance is equipped with an array of tools to scan Martian rocks for signs of ancient life and explore their environmental context.

Also unlike Vikings, rovers can move. Perseverance targets interesting rock formations from a distance—with the help of a helicopter navigator, Creativity—and then drives up there for a closer look.

It also means that persistence, which is storing samples in a cache that will be returned to Earth later, has an advantage over previous investigations that lack context for what they found. “This well-appointed rover gets all of that context because it does all of those great measurements,” said Hayes.

Other possible future places to look for signs of life include sites where underground water collected on ancient Mars, which once formed a system of subterranean lakes.

The search for life elsewhere in the solar system

Little is known about the deep, ice-covered oceans of the outer moons of the solar system, such as Jupiter’s moons Europa, Enceladus, and Saturn’s Titan. But one thing is already clear: they would provide very different conditions for potential life than Mars.

However, these sunless aquatic environments may contain known organic matter and associated chemistry, and even a heat source—the moons’ internal heat, possibly escaping through vents in the ocean floor. It is one of the ways life may have begun on Earth.

During a 13-year mission that ended in 2017, NASA Cassini The spacecraft detected plumes of salty water and organic particles spewing from fractures known as “tiger stripes” on Enceladus – possibly from the moon’s subterranean ocean, indicating a possible habitable environment.

Europa may have similar plumes: data from NASA’s Galileo spacecraft and the Hubble telescope, as well as ground-based telescopes, have indicated its presence. NASA’s Europa Clipper spacecraft, which is now being assembled for a potential launch in October 2024, will carry sensors capable of analyzing any plume of matter it might encounter in a series of flybys over the ice-covered moon.

And while Saturn’s Titan is best known for its thick hydrocarbon atmosphere and lakes of ethane and methane, it’s likely an oceanic world too — like the others, hiding a deep ocean of liquid water under an icy crust. If the Earth’s interior somehow contacted the surface – now or in the past – evidence could be found of molecules or chemistry indicating the possibility of life there. NASA’s Dragonfly mission, a rotorcraft, will search for such evidence on a mission planned for the mid-2030s.

Although the environments of Mars and the outer moon are vastly different, the principles for searching for life remain the same.

“What we’ve learned about life on Earth is that as long as there are some basic things like nutrients, water and energy, we will find life,” Vojtek said. We believe that many environments within the solar system meet these requirements. But it has not been explored yet.”

Looking for life