Mars’ atmosphere is composed of over 95 per cent CO2, yet up until now, researchers have known very little about how it interacts with the surface of the planet.
Now, scientists have found that strange seasonal patterns on the surface of Mars are made by freezing and melting of gas not water.
The red planet has gullies that appear and then disappear on its sand dunes, much like how water forms them on Earth. And it appears ‘carbon dioxide sublimation’ – the process by which a substance changes from a solid to a gas without an intermediate liquid phase – is responsible.
Experts believe newly-discovered phenomenon is unlike anything seen on Earth.
Strange seasonal patterns on the surface of Mars are made by freezing and melting of gas not water, a new study found
THE STUDY
The researchers built a low humidity chamber and placed CO2 blocks on the granular surface which revealed sublimating CO2 can form a range of furrow morphologies that are similar to those observed on Mars.
Linear gullies are an example of active Martian features not found on Earth.
They are long, sometimes sinuous, narrow carvings thought to form by CO2 ice blocks which fall from dune brinks and ‘glide’ downslope
By sliding dry ice blocks onto the sand bed in the low humidity chamber, the group showed that stationary blocks could erode negative topography in the form of pits and deposit lateral levees. In some cases, blocks sublimated so rapidly that they burrowed beneath the subsurface and were swallowed up by the sand in under 60 seconds.
3D models of the modified bed in each case showed the dimensions could be used to predict the range of block sizes that would erode the pits seen on Mars. A pit on Russell Crater megadune on Mars was observed to grow within one Mars Year to an extent predicted by these calculations, following the observation of a block within it the previous year.
The sublimation happens during Mars’ winter which are cold enough to freeze gas into blocks which then gouges out the patterns in the sand and then as spring comes the block ‘melts,’ according to researchers from Trinity College Dublin. Lauren McKeown, one of the researchers who worked on the study, said: ‘We’ve all heard the exciting news snippets about the evidence for water on Mars.
‘However, the current Martian climate does not frequently support water in its liquid state, so it is important that we understand the role of other volatiles that are likely modifying Mars today.
‘Mars has seasons, just like Earth, which means that in winter, a lot of the CO2 in the atmosphere changes state from a gas to a solid and is deposited onto the surface in that form.
‘The process is then reversed in the spring, as the ice sublimates, and this seasonal interplay may be a really important geomorphic process.’
Dr Mary Bourke, another author of the study, added: ‘Several years ago I discovered unique markings on the surface of Martian sand dunes.
‘I called them Sand Furrows as they were elongated shallow, networked features that formed and disappeared seasonally on Martian dunes.
‘What was unusual about them was that they appeared to trend both up and down the dune slopes, which ruled out liquid water as the cause.
