By studying the chemical elements on Mars, including carbon and oxygen, scientists can reconstruct the history of a planet that once had the necessary conditions to harbor life.
Space probes and rovers on Mars have confirmed that the planet once had liquid water, thanks to clues that include dry riverbeds, ancient shorelines, and salty surface chemistry.
Using NASA’s Curiosity rover, scientists have found evidence of long-lived lakes. They also unearthed organic compounds, or chemical components of life. The combination of liquid water and organic compounds forces scientists to keep looking for signs of past or present life on Mars.
Despite the tantalizing evidence found so far, scientists’ understanding of Martian history is still unfolding, with several important questions open for debate.
On the one hand, was the ancient atmosphere of Mars thick enough to keep the planet warm, and therefore humid, for the time necessary to germinate and nurture life? And organic compounds: are they signs of life or chemistry that occurs when Martian rocks interact with water and sunlight?
In a recent Nature Astronomy report on a multi-year experiment conducted in the SAM chemistry lab on board the Curiosity rover, a team of scientists offers some ideas to help answer these questions.
The team discovered that certain minerals in rocks in Gale Crater may have formed in an ice-covered lake.
These minerals may have formed during a cold stage sandwiched between warmer periods, or after Mars lost most of its atmosphere and began to cool permanently.
Gale Crater was selected as Curiosity’s landing site in 2012 because it had signs of past water, including clay minerals that could help trap and preserve ancient organic molecules.
In fact, while exploring the base of a mountain in the center of the crater, called Mount Sharp, Curiosity found a 304-meter-thick layer of sediment that was deposited as mud in ancient lakes.
To form so much sediment, a large amount of water would have flowed into those lakes for millions to tens of millions of warm, humid years, some scientists say.
But some geological features in the crater also hint at a past that included cold and icy conditions.
“At some point, the surface environment on Mars must have undergone a transition from warm and humid to cold and dry, as it is now, but exactly when and how that happened remains a mystery,” says Heather Franz. She is a NASA geochemist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Franz, who led the SAM study, points out that factors such as changes in the obliqueness of Mars and the amount of volcanic activity could have caused the Martian climate to alternate between hot and cold over time. This idea is supported by chemical and mineralogical changes in Martian rocks showing that some layers formed in colder environments and others in warmer environments.
In any case, Franz says, the variety of data collected by Curiosity so far suggests that the team is seeing evidence of Martian climate change recorded on the rocks.
Franz’s team found evidence of a cold, ancient environment after the SAM laboratory extracted carbon dioxide or CO2 and oxygen gases from 13 dust and rock samples.
These samples were collected by Curiosity over the course of five Earth years.
CO2 is a molecule of a carbon atom linked with two oxygen atoms, with carbon as a key witness in the case of the mysterious Martian climate. In fact, this simple but versatile element is as critical as water in finding life elsewhere.
On Earth, carbon continuously flows through air, water, and the surface in a well-understood cycle that depends on life. For example, plants absorb carbon from the atmosphere in the form of CO2. In return, they produce oxygen, which humans and most other life forms use for respiration in a process that ends with the release of carbon into the air, again through CO2, or into the Earth’s crust as life forms die and are buried.
Scientists are discovering that there is also a carbon cycle on Mars and are working to understand it.
With little water or abundant life on the surface of the Red Planet for at least the past 3 billion years, the carbon cycle is very different from that of Earth.
“However, the carbon cycle continues to occur and is still important because it not only helps reveal information about the ancient climate of Mars,” says Paul Mahaffy. He is a Principal Investigator for SAM and Director of NASA Goddard’s Solar System Exploration Division.
“It also shows us that Mars is a dynamic planet that is circulating elements that are the building blocks of life as we know it.”
In this link you can find more information about this research.
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This article is a compilation of material previously published by NASA.