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 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.
‘At that time I proposed that they had been formed by cryo-venting – a process whereby pressurised CO2 gas beneath the seasonal ice deposit erodes complex patterns on the dune surface when the ice fractures and releases the gas in towering dust and gas geysers.
‘What was required was a demonstration of how sand would respond to sublimation of CO2 ice, and this published work is an important step in providing that required proof.’
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’
The researchers designed and 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 another 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.
Miss McKeown said: ‘The difference in temperature between the sandy surface and the CO2 block will generate a vapour layer beneath the block, allowing it to levitate and manoeuvre downslope, in a similar manner to how pucks glide on an ice-hockey table, carving a channel in its wake.
‘At the terminus, the block will sublimate and erode a pit. It will then disappear without a trace other than the roughly circular depression beneath it.
‘While gullies on Earth are commonly formed by liquid water, they almost always terminate in debris aprons and not pits.
Linear gullies are another 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
‘The presence of pits therefore provides more support for a hypothesis whereby CO2 blocks are responsible for linear gullies.’
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.
Professor Jim McElwaine another author of the study, said: ‘This process is really unlike anything seen to occur naturally on Earth – the bed appears fluidised and sand is kicked up in every direction.
The unique markings on the surface are called Sand Furrows as they are elongated shallow, networked features that form and disappear seasonally on Martian dunes (artist’s impression pictured)
‘When we first observed this particular effect, it was a really exciting moment.’
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, which vary in diameter from 1 m to up to 19 m.
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 researchers will now head to the Open University Mars Chamber to assess the influence of Martian atmospheric conditions on these new geomorphic processes.