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How land features could have formed on Mars without much water

The questions we posed in our experiment were: how does the boiling affect transportation mechanisms?

Jan Raack | The Conersation 

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The of Mars, with its dune flows, gullies and slope movements, is the result of sediment being transported downwards in the recent past as well as today. But this “mass wasting”, typically caused by flows of – for example, how the gullies on Earth are shaped – has proved a mystery to planetary scientists. This is because it is assumed that huge amounts of are needed to form these features.

The problem is, there is a lack of enough on now and in the planet’s recent past. In a new study published in Nature Communications, we simulated the atmospheric conditions on to discover how these features could have come about without a big flow of

For example, scientists have made assumptions about the water budget necessary to form the so-called “recurring slope lineae” – dark streaks at the surface which appear annually (687 days) during peak and which dissolve in colder months at the martian But the needed to create these features would be too high to come from the martian weather each year.

Dark streaks on the planet’s which appear annually. NASA/JPL/University of Arizona, Author provided

In our experiments, however, we identified that it is possible to transport sediment down a slope without the need for so much We did this using the Simulation Chamber, specialised equipment that is able to simulate the atmospheric conditions on

Unique set of conditions

To explain how mass wasting can happen without lots of water, it’s important to know that the present-day atmosphere of is very thin – the mean pressure is around 7mb (millibars) (compared to 1,000mb on Earth). In relatively recent times (around 20m years) the pressure has also been low. These low pressures mean that liquid will boil at low sediment of around 5°C. It means that liquid will effectively “levitate” on the of (when are above the zero). This “levitating” and can entrain a large amount of sand and other sediment when flowing down a slope.

This process would require much less than would be needed otherwise.

With this background information we wanted to test how liquid flows behave under low pressures and with relatively warm surfaces (between 5°C and 24°C, which is warm for surfaces of Mars, but not impossible). The questions we posed in our experiment were: how does the affect transportation mechanisms? Will there be more or less sediment transported with the effect of And can we see new transportation mechanisms taking place?

Previous work has investigated sediment transport by liquid or melting ice under martian conditions, but the phenomenon of levitation or hovering of a water-sediment mixture over warm sediment was not observed in their experiments. This phenomenon is comparable with the so-called “Leidenfrost effect”, easily seen when you put some drops on a hot cooking plate. The sublimates immediately and the drop floats on a cushion of gas emanating from the drop. This mechanism could also happen on Mars, but as described before with much lower slightly above the frost point.

Our experiments show that this phenomenon can move huge amounts of sediment down a slope without the need for much – around nine times more sediment was moved down a slope with the effect of levitation than without the effect. Our model also showed that the lower gravity on would have a positive effect on levitation: with lower gravity we would expect an increased rate of the amount of transported sediment over longer distances.

This means in particular for that it is possible to explain already observed mass movements on its with the involvement of less than previously predicted and that the amount of needed for some transportation processes could have been previously been overestimated.

The caveat

The “warm” sediment we chose for our experiments are possible on So the effect of levitation could only occur when sediment are relatively high (the annual mean temperature is about -55°C, but can rise up to around 30°C during the day in the summer).

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The question of a possible origin of the needed for the levitation could not be solved during our experiments, and also here further work has to be made to solve this uncertainty. Nevertheless, our experiments show that such a mechanism is possible on (when the parameters are correct) and should be taken into account when thinking about water-related mass wasting features on Our experiments will not give the answer of how recent and present-day mass wasting features of the martian (in particular gullies and recurring slope lines) are forming, but we do provide a new perspective.

Jan Raack, Research Fellow, The Open University

This article was originally published on The Conversation. Read the original article.

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First Published: Mon, October 30 2017. 10:58 IST