Geomorphologist Dr Mary Bourke examines ripples on a sand dune on Earth, but imaging technology also allows her to analyse dunes on Mars
New imaging and technologies mean we are getting an unprecedented view of the Martian landscape – and it’s throwing up some surprises. Claire O’Connell finds out from geomorphologist Dr Mary Bourke about the dynamic – and exploding – surface of the red planet.
Mars has never felt more familiar. With orbiters circling it and robotic rovers trundling across its surface – even tweeting ‘selfies’ from our planetary neighbour (I’m looking at you, @MarsCuriosity) – the landscape of Mars is truly on our radar.
But what do we really know about that landscape? Our understanding of it is changing, thanks to improved imaging technology, and Mars is a more dynamic place than we might previously have thought, according to Bourke. She’s a geomorphologist at Trinity College Dublin, and she is discovering active processes in the Martian landscape that challenge any notion of it being a ‘dead’ terrain.
Fast and furious
Mars is one of many extreme environments that have captured her attention since she studied geography at University College Dublin. “My interests have always been in things that happen either fast or furiously,” says Bourke, who did her master’s thesis on the impact in Ireland of Hurricane Charley. “I looked at the landslides and flooding, it was all really dynamic stuff.”
For her PhD at the Australian National University, Bourke looked at the landscape around Alice Springs to date catastrophic floods back through millennia, providing valuable information for flood-mitigation strategies in the area. That work earned her a stint at the Smithsonian Institution, looking at images of flood traces on Mars, and this is where she caught the Mars bug.
And again, it is an extreme environment, she explains. “It is extremely old in terms of its surface features, and because of the lack of atmosphere there is an extreme fluctuation between cold and heat in a daily cycle. For example, @MarsWxReport informs us that on April 1st the high was 1.95ºC and the low was -69ºC.”
Technology gives a better view
After a few years in Oxford University, Bourke moved to the Planetary Science Institute in Tucson, Arizona, a not-for-profit organisation where scientists are funded by NASA and the National Science Foundation to study other planets.
She developed a particular interest in dune formation on Mars, and the carbon-dioxide ice that covers them at the polar caps of the planet. And in recent years, the quality of the images beamed back from the Mars Reconnaissance Orbiter has meant she can look right up close at the landscape.
“In these exquisitely high-resolution images I can now see the ripples on the surface of dunes,” says Bourke. “And because the camera has been in orbit for more than three Mars years (about six Earth years) we are able to go back to specific sites and see the changes that have been happening.”
Exploding dunes
So what is happening? Bourke has found that from Mars year to Mars year, the surface features on the dunes change, and she has found that wind moves the ripples.
She also recently shed new light on a new way that sediment is moved on dunes. It’s a phenomenon she terms cryo-venting, where the carbon dioxide ice-capped dunes around the poles of Mars ‘explode’ and spray out sediment. The sediment spraying itself has been observed on the southern icy terrains since the 1990s, but had not been observed on dunes before, she explains.
“During the polar spring, the carbon-dioxide ice becomes see-through and sunlight can penetrate through it, heating the dune surface and creating a little greenhouse-like effect,” she says. “The heat causes the ice to sublime right there between the top of the dune and the bottom of the seasonal ice cap, the ice starts to fracture from the pressure build-up, huge fans of ice and sand explode out of these cracks and you get these dark fans of sediment that spread all over the dunes.”
By looking at the cracks in the ice and afterwards at the surface of the dunes when the ice has gone, Bourke has discovered there seems to be an active component to this process and the effects it has on the underlying landforms.
“The sediment ejections form small sinuous furrows on the surface of dunes, so when the ice goes away the dunes are left covered in these furrows,” she says. “By doing basic geomorphic mapping you find that they are not only forming these patterns that look like small rivers that are sinuous or braiding, but also that they go up one side and down the other side of a dune – defying gravity. This confirmed that the forming fluid was not flowing liquid but a gas under pressure- the subliming carbon-dioxide gas.”
There is no analogue for such a process on Earth, she adds. “It really is extra-terrestrial – and when you are part of a frontier science, which is what planetary geomorphology is, new discoveries are part and parcel of what we do.”
Mars inspires
Bourke, who last year moved to Trinity to take up the post of assistant professor at the Department of Geography, is encouraged to see so much media interest in Mars at the moment. “At its very basis, it helps to get science out of the laboratory and get people excited about new science discoveries,” she says. “And even with my own students, Mars is a completely inspirational topic for them – it inspires them about learning and doing research. It’s no longer about the planet we live on, it’s about the solar system we live in.”
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