There’s a reason Persistence got where it happened, and that reason goes back at least 3.5 billion years.
Early Mars is thought to be like Earth before solar radiation and other cosmic forces killed the atmosphere. This explains why the rover that has now gone viral in the Twitterverse and landed just about everywhere else in Jezero Crater, which is thought to be once a massive lake that was also teeming with microbial life. Scientists have now found evidence that Mars went through the same phase as Earth before both planets got their atmospheres – something that has not been proven so far.
“Reduced greenhouse gases such as methane (CH4) and hydrogen (H2) could be the only viable solution to explain the warming of the ancient Martian climate, but direct geological evidence that a diminished atmosphere actually existed on Mars was lacking,” said Jiancheng Liu . , who led a study recently published in Nature Astronomy.
The timing for this discovery was just right. Perseverance has begun to search the Red Planet for possible signs of life, and that life – if it was anything like it as we know it – would have needed an atmosphere. But wait. Before you can figure out when Mars started getting an atmosphere, and what it was like with an atmosphere (hard to imagine when you look at what is now a space desert), you need to back it up before it even got an oxidized atmosphere. There is a time when things on Earth or Mars didn’t rust because there wasn’t enough oxygen in the atmosphere to interact with substances rich in iron.
Rather than an oxidized atmosphere, both Earth and Mars once had a diminished atmosphere. This is not the same as the tremendous reduction in atmosphere the Red Planet experienced after most of its atmosphere was decimated by solar winds and other cosmic forces. A reduced atmosphere consists mainly of reduced gases such as methane, ammonia and hydrogen sulfide, which are rich in hydrogen rather than oxygen. Humans would not have been able to inhale this poison. However, there are microorganisms that are fed by methane here on our planet, so it wouldn’t be impossible for Mars.
What once made Mars habitable was its own greenhouse effect. While greenhouse gases have been demonized on Earth because too much carbon dioxide and other species have entered the atmosphere through human pollution, it takes the right amount of these atmospheric gases to heat up a planet just enough for life forms to thrive.
Previous studies had assumed that this phenomenon happened on Mars with reduced gases instead of CO2, meaning the planet must have had a reduced atmosphere. Evidence of this was eventually found by Liu and his team when they examined spacecraft data of weathered Mars rocks that showed signs of exposure to such an atmosphere.
“The separation of Fe and Al in Martian paleosols, which is similar to trends observed in paleosols before Earth’s Great Oxidation Event, suggests that the ancient Martian surface was chemically weathered under a declining greenhouse atmosphere,” said Liu.
A spacecraft in orbit explored remote rocks on the surface of Mars. This spacecraft was equipped with an instrument capable of infrared spectroscopy, which revealed the chemistry of these ancient rocks. When infrared light hits a target, it interacts with the molecules that make up that object. How the object in question absorbs, reflects or emits this light can reveal its chemical composition. What the researchers wanted to know was the composition of the paleosols on Mars, soils formed centuries ago that are physically and chemically unrelated to soils that have recently formed. In this way they identified a chemical sign of weathering caused by a diminished atmosphere.
Mars later underwent an oxidation event much of Earth’s great oxidation event on Earth, though at a different time and possibly for different reasons. Earth’s atmosphere became oxidized because oxygen was a byproduct of processes such as photosynthesis in early organisms. Evidence that Mars had a diminished atmosphere before the oxidation occurred could mean that somehow life was involved in the shift.
As Perseverence investigates Jezero Crater, it may find more to support this discovery, and perhaps even a fossilized microbe.