The Atmospheric Chemistry Suite (ACS) aboard ESAs ExoMars Trace Gas Orbiter (TGO) has spotted never-before-seen spectral signatures of ozone and carbon dioxide in the Martian atmosphere.

ESAs ExoMars Trace Gas Orbiter at Mars. Image credit: D. Ducros / ESA.

The atmosphere of Mars is dominated by carbon dioxide, which scientists observe to gauge temperatures, track seasons, explore air circulation, and more.

Ozone, which forms a layer in the upper atmosphere on both Mars and Earth, helps to keep atmospheric chemistry stable.

Both carbon dioxide and ozone have been seen at Mars by spacecraft such as ESAs Mars Express, but the exquisite sensitivity of the ACS instrument was able to reveal new details about how these gases interact with light.

These features are both puzzling and surprising, said Dr. Kevin Olsen, a researcher at the University of Oxford.

They lie over the exact wavelength range where we expected to see the strongest signs of methane.

Before this discovery, the carbon dioxide feature was completely unknown, and this is the first time ozone on Mars has been identified in this part of the infrared wavelength range.

This graph shows an example of the measurements made by the Atmospheric Chemistry Suite (ACS) on ESAs ExoMars Trace Gas Orbiter, featuring the spectral signatures of carbon dioxide (CO2) and ozone (O3). The bottom panel shows the data (blue) and a best-fit model (orange). The top panel shows the modeled contributions from a variety of different gases for this spectral range. The deepest lines come from water vapor (light blue). The strongest O3 feature (green) is on the right, and distinct CO2 lines (gray) appear on the left. The locations of strong methane features (orange) are also shown in the modeled contributions, though methane is not observed in the TGO data. Image credit: Olsen et al, doi: 10.1051/0004-6361/202038125.

One of the key objectives of TGO is to explore methane. While also generated by geological processes, most of the methane on Earth is produced by life, from bacteria to livestock and human activity.

Detecting methane on other planets is therefore hugely exciting. This is especially true given that the gas is known to break down in around 400 years, meaning that any methane present must have been produced or released in the relatively recent past.

Discovering an unforeseen carbon dioxide signature where we hunt for methane is significant, said Dr. Alexander Trokhimovskiy, a scientist at the Space Research Institute.

This signature could not be accounted for before, and may therefore have played a role in detections of small amounts of methane at Mars.

The new findings enable us to build a fuller understanding of our planetary neighbor, he added.

Ozone and carbon dioxide are important in Mars atmosphere. By not accounting for these gases properly, we run the risk of mischaracterizing the phenomena or properties we see.

Mars is about half the size of Earth by diameter and has a much thinner atmosphere, with an atmospheric volume less than 1% of Earths. The atmospheric composition is also significantly different: primarily carbon dioxide-based, while Earths is rich in nitrogen and oxygen. The atmosphere has evolved: evidence on the surface suggests that Mars was once much warmer and wetter. Understanding if life could have ever existed in such conditions is one of the hot topics of Mars exploration. The ExoMars Trace Gas Orbiter is capable of sniffing out the composition of the planets trace gases, which make up less than 1% by volume of a planets atmosphere, in minute amounts. Although making up a very small amount of the overall atmospheric inventory, methane in particular holds key clues to the planets current state of activity. On Earth, living organisms release much of the planets methane. It is also the main component of naturally occurring hydrocarbon gas reservoirs, and a contribution is also provided by volcanic and hydrothermal activity. Because of the key role natural biology plays in Earths methane production, confirming the existence of methane on Mars, and distinguishing between its potential sources, is a top priority of the ExoMars Trace Gas Orbiter. Image credit: ESA.

Additionally, the surprising discovery of the new carbon dioxide band at Mars, never before observed in the lab, provides exciting insight for those studying how molecules interact both with one another and with light and searching for the unique chemical fingerprints of these interactions in space.

Together, these two studies take a significant step towards revealing the true characteristics of Mars: towards a new level of accuracy and understanding, Dr. Trokhimovskiy said.

The results were published in two papers in the journal Astronomy & Astrophysics.

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K.S. Olsen et al. 2020. First detection of ozone in the mid-infrared at Mars: implications for methane detection. A&A 639, A141; doi: 10.1051/0004-6361/202038125

A. Trokhimovskiy et al. 2020. First observation of the magnetic dipole CO2 absorption band at 3.3 m in the atmosphere of Mars by the ExoMars Trace Gas Orbiter ACS instrument. A&A 639, A142; doi: 10.1051/0004-6361/202038134

This article is based on a press-release provided by the European Space Agency.

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ESA's Trace Gas Orbiter Detects Ozone and Carbon Dioxide in Atmosphere of Mars | Planetary Science, Space Exploration - Sci-News.com