by Is there or was there life on Mars? That deep question is so complex that it won’t be fully answered by the two NASA rovers now being explored.
But because of the literal groundwork the rovers are doing, scientists are finally probing, in unprecedented depth and detail, the planet’s evidence for life, known as its “biosignatures.” This search is extremely complex, and in the case of Mars, it spans years.
As a geologist, I had the great opportunity to work on both the Curiosity and Endurance rover missions. But as much as scientists are learning from them, it will take another robotic mission to determine whether Mars ever hosted life. That mission will bring Martian rocks back to Earth for analysis. Then – hopefully – we will have an answer.
From habitable to uninhabitable
Although there is still so much mystery about Mars, there is one thing I am sure of. Among the thousands of pictures being taken by the two rovers, I’m pretty sure none of them will show exotic bears or meerkats. Most scientists doubt that the surface of Mars, or its near surface, could currently support even single-celled organisms, much less complex life forms.
Instead, the rovers are acting as extraterrestrial detectives, looking for clues that life might have existed long ago. This includes evidence of long-gone liquid surface water, life-sustaining minerals and organic molecules. To find this evidence, Curiosity and Perseverance are walking very different paths on Mars, more than 2,000 miles (3,200 kilometers) apart.
These two rovers will help scientists answer some big questions: Has there ever been life on Mars? Could it exist today, perhaps deep below the surface? And would it just be microbial life, or is there any possibility that it could be more complex?
The Mars of today is not like the Mars of a billion years ago. In its beginnings, Mars was much more like Earth, with a thicker atmosphere, rivers, lakes, perhaps even oceans of water, and the essential elements needed for life. But this period was reduced when Mars lost its magnetic field and almost its entire atmosphere – now it is only 1% as dense as Earth.
The change from habitable to uninhabitable took time, perhaps hundreds of millions of years; if life ever existed on Mars, it probably died out a few billion years ago. Gradually, Mars became the cold and dry desert it is today, with a landscape comparable to the dry valleys of Antarctica, without glaciers and plants or animals. The average Martian temperature is minus 80 degrees Fahrenheit (minus 62 degrees Celsius), and its thin atmosphere is all carbon dioxide.
Early exploration
Robotic exploration of the Martian surface began in the 1970s, when life detection experiments on the Viking missions failed to find any conclusive evidence for life.
Sojourner, the first rover, landed in 1997 and showed that a moving robot could perform experiments. In 2004, Spirit and Opportunities continued; Both found evidence that liquid water once existed on the Martian surface.
The Curiosity rover landed in 2012 and began its ascent of Mount Sharp, the 18,000-foot-tall mountain located inside Gale crater. There’s a reason NASA chose it as an exploration site: The mountain’s rock layers show a major change in climate, from one with plenty of liquid water to today’s dry environment.
So far, Curiosity has found evidence in several past locations of liquid water, minerals that could provide chemical energy, and interestingly, a variety of organic carbon molecules.
Although organic carbon itself is not living, it is a building block for all life as we know it. Does their presence mean that there was once life on Mars?
It is not necessary. Organic carbon can be abiotic – that is, not associated with a living organism. For example, the organic carbon may have come from a meteorite that crashed on Mars. And although the rovers carry amazingly sophisticated instruments, they cannot tell us definitively if these organic molecules are related to past life on Mars.
But labs here on Earth probably can. By collecting rock and soil samples from the Martian surface, and then sending them back to Earth for detailed analysis with our state-of-the-art instruments, scientists may finally have an answer to the question of age.
Persistence
Enter Persistence, NASA’s newest flagship mission to Mars. For the past three years – it landed in February 2021 – it has persevered in searching for signs of microbial life buried in the rocks within the Jezero crater, which was chosen as a landing site because it was once a large lake.
Persistence is the first phase of the Mars Sample Return mission, an international effort to collect Martian rock and soil for return to Earth.
The suite of instruments on board Persistence will help the science team select the rocks that appear to have the most scientific results available. This will be a careful process; after all, there would only be 30 seats on the return trip to Earth for these geological samples.
The budget reads
NASA’s original plan called for those samples to be returned to Earth by 2033. But work on the mission – now estimated to cost between US$8 billion and $11 billion – has been delayed by budget cuts and layoffs. The cuts are tough; a request for $949 million to fund the fiscal 2024 mission was trimmed to $300 million, although efforts are underway to restore at least some of the funding.
The Mars Sample Return mission is critical to better understanding the potential for life beyond Earth. The science and technology that will enable it is novel and expensive. But if NASA discovers that life once existed on Mars – even if microbes are found dead for a billion years – it will tell scientists that life on Earth was not just a one-off event, but a more common phenomenon that could to be there occurs on many planets.
That knowledge would revolutionize the way humans see ourselves and our place in the universe. There is much more to this effort than just bringing back some rocks.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. Written by: Amy J. Williams, University of Florida
Read more:
Amy J. Williams receives funding from NASA Participating Scientist grants related to the Mars 2020 Endurance rover and the Mars Science Laboratory Curiosity rover.
