Planetary scientists discover evidence for reduced atmosphere on ancient Mars

Both Earth and Mars currently have oxidizing atmospheres, and therefore iron-rich materials develop corrosion in everyday life (a common name for iron oxide) during the oxidation reaction of iron and oxygen. The earth has had an oxidizing atmosphere for about 2.5 billion years, but before that the atmosphere of this planet diminished – there was no rust.

The transition from a reduced planet to an oxidized planet is called the Great Oxidation Event or GOE. This transition was a central part of the evolution of our planet and was fundamentally linked to the evolution of life here – specifically with the advent of photosynthesis that produced oxygen. Planetary geologists at HKU have discovered that Mars has undergone a major oxygen event of its own – billions of years ago the red planet was not so red.

The discovery was made recently in Natural Astronomy in a paper led by postgraduate research student Jiacheng LIU and his adviser, associate professor dr. Joe MICHALSKI, both affiliated with the Division of Research for Earth and Planetary Science and the Laboratory for Space Research. The researchers used infrared remote sensing and spectroscopy to measure the molecular vibration of the material on the Martian surface from an orbit, to reveal the mineralogy and geochemistry of ancient rocks on Mars. Through detailed comparisons of infrared data for remote sensing and data collected in the laboratory here on Earth, the team showed that ancient rocks on Mars exposed to the surface were weathered under reduced conditions, indicating a reduced atmosphere.

Many people are aware that Mars is now cold and dry, but ~ 3.5 billion years ago it was warmer and wetter. It was hot enough to form river channels, lakes and minerals that formed through interaction with water. Scientists who used mathematical models to limit the conditions of an early Martian atmosphere concluded that greenhouse warming had occurred, but they also concluded from their models that the greenhouse should contain fewer gases rather than carbon dioxide, and implied that the diminished atmosphere might have existed. Until now, there has been no evidence that the diminished atmosphere of early Mars actually took place. This work indicates that it did exist.

This project involved detailed infrared remote sensing of Mars, using infrared spectroscopy to map minerals in exposed, weathered rock units. The work was built on detailed analysis of weathered volcanic rocks on Hainan Island in southwest China, where thick rows of basalt, similar to volcanic rocks on Mars, occur. Jiacheng Liu systematically analyzed the altered rocks using infrared spectroscopy in the laboratory and published a paper on the research recently published in Applied Clay Science.

“Jiacheng has carried out a truly excellent Ph.D. project, building on careful laboratory analysis and applying the laboratory results to remote sensing from Mars,” said Dr. Michalski said: “Jiacheng built on his detailed work on samples from Hainan Island to show that similar mineral trends occurred in rocks on Mars.”

Assistant Professor dr. Ryan MCKENZIE of the Division of Research for Earth and Planetary Science is also impressed by these findings. “This is a rather remarkable study with findings that will have a significant impact on the way we understand the early evolution of terrestrial planets and their surface environments. The transition from a reducing to oxidizing atmosphere on Earth ~ 2.5 billion years ago was only possible because the existence of life, as oxygen is a waste product of metabolic processes such as photosynthesis, without microbes producing oxygen, it would not accumulate in our atmosphere, and we could not be here. ‘While there are differences in the local conditions to which Mars and Earth are subject, their evolutionary history can not help my mind begin to reflect on what Jiancheng’s results could mean for a potential early Mars biosphere,’ Dr. McKenzie noted.

As China’s first mission to MarsTianwen-1 is underway – arrived successfully in Mars orbit on February 10 and would land on Mars in May 2021, scientists are preparing for an exciting year of discovery and discovery of Mars. This work shows how spectroscopy and remote sensing lead to fundamental discoveries that are of great importance for understanding the history of Mars. As we begin to understand the oldest history of Mars, researchers are ready to search directly for any signatures that life could ever have on ancient Mars, and HKU plans to be the center of this great scientific adventure.