When NASA’s Perseverance rover begins surveying the Martian surface in the coming months, the robotic explorer will be searching for signs of ancient life. Then, “Percy,” as she’s known to her team on Earth, will actually collect those samples, and future missions will return them to Earth.
Perseverance is NASA’s first true astrobiology mission in the search for evidence of life on another planet in our solar system.
The rover is looking for clues that will help answer a question that has intrigued humans for millennia: Is there life beyond Earth?
While samples from Mars could reveal the planet’s past, future missions to other intriguing worlds in our solar system could illuminate something else. In 2017, NASA announced that ocean worlds, like Saturn’s moons of Titan and Enceladus and Jupiter’s moon Europa, may be the most likely places to find life beyond Earth.
Two missions are scheduled to launch this decade to explore Titan and Europa in an effort to understand if these intriguing worlds could host life within their subsurface oceans and reservoirs. Europa Clipper is set to launch in 2024, while Dragonfly is slated for 2027.
“Perseverance will get people thinking in terms of astrobiology and the strategy of looking for signs of past life,” said Jorge Núñez, astrobiologist at the Johns Hopkins University Applied Physics Laboratory, who is working on teams for both Perseverance and Dragonfly.
“Missions to outer planets, like Europa and Dragonfly, will take a lot of time. But we have to be open to what we might be able to find in terms of possibilities for life. These missions are part of this strategy in trying to understand how environments evolve. Is life a more common thing, or is it rare? And what is out there?”
Searching for ancient fossils on Mars
Currently, Mars seems like an inhospitable place for humans – and its global dust storms haven’t been too kind to previous rovers, either. The planet is a frozen desert with a thin atmosphere. It’s hard to imagine life existing there.
However, 3.9 billion years ago, it was a different story.
Jezero Crater, where Perseverance has landed, was once filled with water and may have been surrounded by white sandy beaches, as indicated by a “bathtub ring” of minerals left behind in the dry lake bed today. A river delta fed in to one side of the lake and another river channel of overflow from the lake emerged on the other side.
For the next two years, Perseverance will traverse the crater floor and river delta, studying rocks, minerals and dirt and their chemical compositions. Microfossils of ancient microbial life could be trapped inside of them.
“We study the formation, preservation and detection of signs of life and planetary evolution in geologic samples,” said astrobiologist Ken Williford, the deputy project scientist for the Perseverance rover.
“The instruments on rover missions are sort of portable versions of instruments we have in labs like mine and other labs that work on ancient rocks and measure the chemistry and shapes preserved in them,” added Williford, who is also the director for the abcLab at NASA’s Jet Propulsion Laboratory in Pasadena, California. The “abc” in abcLab is short for astrobiogeochemistry.
Rocks are a wealth of information, preserving notes from when they were formed. They include clues about chemistry, climate change and if organisms were present.
While much of the lab work focuses on Earth, this approach can also be used to interpret possible signs of life elsewhere, like Mars.
Using Perseverance’s advanced suite of instruments and cameras, the science team on Earth will have their best look yet at rocks on Mars that could reveal the planet’s past.
“We’re looking for lifelike compositions and shapes that occur together,” Williford said. “Carbon-based life is made of organic matter. They fossilize, get buried, squished and squeezed and turned into organic goo like oil or coal.”
This goo ends up in rocks, so “ancient organic matter may be the very old bodies of Martian microbes,” he said.
Scientists aren’t expecting to find fossils like those belonging to dinosaurs on Mars, but microbial life is a much better possibility if it ever existed on Mars.
Just look at Earth. Microbial life existed for a long time before more complex types of life evolved. In Earth’s earliest fossil record, scientists study fossilized pond scum rather than bones or shells.
Fossilized pond scum is basically a group of photosynthetic bacteria that stuck to sediment, forming microbial mats. After the water in their environment dries up, the minerals are left behind and entomb those microbes, forming stromatolites.