WHAT I REALLY WANT TO KNOW IS…
What does Mars smell like?
M ars is a good example of a planet we think has undergone drastic climate change in its early days. It is presently a cold desert, but in winter there are large weather systems very similar in scale to those we experience in the UK. The intriguing question is: while Mars is currently very cold and dry, could it have been warmer and wetter in the past? Certainly, there’s evidence in the rocks on the surface that it was. So was it ever habitable? Could it have even been – in the distant past, four billion years ago or so – a place where life could have started?
My role involves monitoring and understanding the current state of the atmosphere on Mars but also looking for tiny traces of gases that may reveal something about Mars’s past using the Trace Gas Orbiter (TGO) to ‘sniff ’ them out.
The TGO was launched in March 2016 and arrived at the Red Planet in November 2016. There were no observations until it got into its science orbit in late spring of this year. We are now getting science data on a regular basis.
We know that the bulk of the atmosphere is carbon dioxide, nitrogen and a few noble gases, but what we really want to know is are there any other trace gases that don’t fit in with the equilibrium gases that possibly give a hint of something that’s happening on Mars today, or long, long ago?
A very useful heat haze
We are looking down to parts per billion; it takes some very sensitive spectroscopy to find gases that are such tiny components of the atmosphere. So to give us a better chance of finding them, the spacecraft will also be looking as the Sun rises and sets through the Martian atmosphere.
Why? Well, currently TGO is about 400km above the surface, orbiting every couple of hours. In every orbit it sees one sunrise and one sunset. For a brief few minutes as the Sun sets or rises, the TGO will, because of its angle, be looking at it through a long stretch of Mars’s atmosphere; that gives you a large sample for spectroscopy and a greater chance of detecting even minor gases in the atmosphere. This is a technique known as limb sounding. The same instruments used for this will look straight down at the planet as well. This will give us another source of information because the surface is relatively warm and gives off infrared radiation that will be absorbed and re-emitted by gases in the atmosphere as it rises up towards to the TGO.
Life lessons
Why are we doing this? One reason is so that we can test our models of Earth’s climate systems. It might change our ideas about how our own atmosphere works or help us understand what’s important about Earth’s climate, and what causes climates to change and become less habitable. The second reason is learning how Mars has evolved and asking if Mars were ever a habitable place, which opens up some huge questions. Just because life could evolve somewhere, does it always evolve? Or is life still incredibly unlikely? We have only one example: Earth. Was that just an incredible fluke? Of course, you can’t actually smell Mars – if you took your helmet off you’d die fairly quickly. But thinking about what it might smell like is a way speculating about what Mars’s atmosphere might be made up from. The main gases, including carbon dioxide and nitrogen, don’t smell of anything. But we are trying to look for tiny trace amounts of out-of-balance gases. We are not directly smelling them, but looking at their spectra. Essentially, there would be a sort of rusty smell that you’d get from the dust of oxidised rocks. The other smell might be a methane-farty smell – to put it crudely – if there were bacterial or microbial life on Mars. Methane is one of the trace gases we are looking for, but its presence wouldn’t necessarily prove the presence of life, now or ever. It could have come from a totally non-living process, like geothermal activity.