Is there or was there life on Mars? This profound question is so complex that it cannot be fully answered by the two NASA rovers currently investigating it.
But because of the actual groundwork the rovers have performed, scientists are finally investigating the planet’s evidence of life, known as its “biological signatures,” in depth and unprecedented detail. This search is extremely complex and, in the case of Mars, spans decades.
As a geologist, I had the extraordinary opportunity to work on both the Curiosity and Perseverance rover missions. Although scientists are learning from them, it will take another robotic mission to figure out whether Mars hosts life. This mission will bring rocks from Mars back to Earth for analysis. Then – hopefully – we will have an answer.
From habitable to uninhabitable
Although many things about Mars remain mysterious, there is one thing I have confidence in. Of the thousands of photos taken by both rovers, I’m pretty sure none of them will show any alien bears or meerkats. Many scientists doubt that the surface or near-surface of Mars could even support single-celled organisms, much less complex life forms.
Instead, rovers act as extraterrestrial detectives, looking for clues that life may have existed eons ago. This includes evidence of long-vanished 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: Was there life on Mars? Could it exist today, perhaps deep below the surface? And will this just be microbial life, or is it likely to be more complex?
Today’s Mars is nothing like the Mars of a few billion years ago. In its early stages, Mars looked much more like Earth, having a thicker atmosphere, rivers, lakes, perhaps even oceans of water, and the basic elements needed for life. However, this period was shortened as Mars lost its magnetic field and almost all of its atmosphere (now only 1% as dense as Earth’s).
The transition from habitable to uninhabitable took time, perhaps hundreds of millions of years; If life existed on Mars, it probably disappeared several billion years ago. Gradually, Mars became the cold, dry desert it is today, with a landscape comparable to the dry valleys of Antarctica, devoid of glaciers and plant or animal life. Mars’ average temperature is minus 80 degrees Fahrenheit (minus 62 degrees Celsius), and its meager atmosphere consists almost entirely of carbon dioxide.
early discovery
Robotic exploration of the surface of Mars began in the 1970s, when life-detection experiments on the Viking missions failed to find any conclusive evidence for life.
The first rover, Sojourner, landed in 1997 and demonstrated that a moving robot could perform experiments. Spirit and Opportunity followed in 2004; both found evidence that liquid water once existed on the surface of Mars.
The Curiosity rover landed in 2012 and began climbing the 18,000-foot-high Mount Sharp, located inside the Gale crater. There’s a reason NASA chose it as an exploration site: The mountain’s rock layers show a dramatic climate change from an environment with abundant liquid water to today’s dry environment.
So far, Curiosity has found evidence in various locations of past liquid water, minerals that could provide chemical energy, and, surprisingly, a variety of organic carbon molecules.
Although organic carbon is not itself alive, it is the building block of all life as we know it. Does its presence mean that life once existed on Mars?
Not necessarily. Organic carbon may be abiotic, meaning it may not be associated with a living organism. For example, organic carbon may have come from a meteorite that crashed on Mars. Although the rovers carry highly sophisticated instruments, they cannot tell us for sure whether these organic molecules are associated with past life on Mars.
But laboratories on Earth can probably do this. By collecting rock and soil samples from the surface of Mars and sending them back to Earth for detailed analysis with our state-of-the-art instruments, scientists may finally find the answer to an age-old question.
Patience
Enter Perseverance, NASA’s newest flagship mission to Mars. For the past three years — it landed in February 2021 — Perseverance has been searching for signs of bygone microbial life in rocks in the Jezero crater, which was chosen as the landing site because it once contained a large lake.
Perseverance is the first step of the Mars Sample Return mission, an international effort to collect rocks and soil from Mars for return to Earth.
The instrumentation aboard Perseverance will help the science team select rocks that promise the most scientific return. This will be a careful process; Ultimately, there would be only 30 seats for these geological samples on the return journey to Earth.
budget problems
NASA’s original plan called for these samples to be returned to Earth by 2033. However, work on the mission, now estimated to cost between $8 billion and $11 billion, has slowed due to budget cuts and layoffs. The disruptions are severe; The $949 million request to fund the mission for fiscal year 2024 has been reduced to $300 million, but 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 make this possible are both new and expensive. But if NASA discovers that life once existed on Mars — even if it finds a microbe that’s been dead for a billion years — that would tell scientists that life was a more widespread occurrence, not just a random one-off event that happened on Earth. Occurs on many planets.
This knowledge will revolutionize the way humans see ourselves and our place in the universe. There’s much more to this effort than just bringing back some rocks.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and authoritative analysis to help you understand our complex world. Written by: Amy J. Williams, university of florida
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Amy J. Williams receives funding from NASA Participating Scientist grants associated with the Mars 2020 Perseverance rover and the Mars Science Laboratory Curiosity rover.