An icy atmosphere

CO₃ could be the key to formation of interstellar ices.

Heard the one about the boring party on Mars? Apparently there was no atmosphere. So goes the old joke, but the actual composition of both Earthly and Martian atmospheres is being closely monitored by a group of researchers from the US.

The planetary atmospheres of Earth and Mars as well as those of comets contain ices made from carbon dioxide and ozone. The processes that rule the formation of these carbon dioxide ices at low temperatures are something of a mystery.

Ralf Kaiser at the University of Hawai’i at Manou and colleagues from Florida International University, have cooled things right down in the lab and formed carbon trioxide, CO₃, by bombarding carbon dioxide and molecular oxygen with electrons at a very chilly temperature of 10K. Kaiser claims that the molecule is present in the ices found on Mars and has looked at its formation both experimentally and theoretically. The researchers investigated a cyclic version of CO₃ and found that it was the only isomer of this molecule that could be detected. Potentially important as an intermediate in making carbon dioxide ices, it seems that CO₃ might be responsible for the presence of an enriched form of oxygen within atmospheric CO₂. During its decomposition, CO₃ manages to trap the heavy ¹⁸O atom and incorporate it into the resulting product - carbon dioxide.

David Williams, from University College, London, UK, who works on the astrochemistry of star-forming regions, suggests that the detection of CO₃ is a potential breakthrough. ’Carbon trioxide has not yet been detected. the experiments reported here show that conversion of CO₂ to CO₃ can occur. The amount of CO₃ might be detectable. Reactions of this type may be responsible for making quite complex molecules inside interstellar ices.’ So, what does this mean for future Martian visitations?

Could further research in this area eventually lead to interplanetary habitation? Perhaps this isn’t such an outlandish concept; Kaiser himself says ’our experiments suggest that carbon dioxide frosts might have trapped a significant amount of oxygen and ozone which might be utilised in a future colonisation of Mars.’

Katharine Sanderson