We may not have found life on Mars, but we have found ‘spiders’ … of sorts.
They are called araneiform: dark, spider-like systems, false grooves found only in the southern pole regions of the red planet. There is nothing like them on Earth, or any other planet in the Solar System.
That makes it difficult to understand what creates them, but scientists have just found the first physical evidence that supports the most popular model, known as Kieffer’s hypothesis. According to this theory, the spider-like forms are formed by direct sublimation of frozen carbon dioxide (CO2).
“This research presents the first set of empirical evidence for a surface process thought to alter the polar landscape on Mars,” said planetary scientist Lauren McKeown, a former College Trinity in Ireland, and now at the Open University.
“Kieffer’s idea has been accepted for more than a decade, but so far, it has been designed in a purely theoretical context. The experiments directly show that the spider patterns can be seen. we have carved Mars from orbit with a direct turn of dry ice, from solid to gas. “
Mars is both very similar to, and very different from, Earth. Its axial tilt is very close to the Earth, which means that its seasonal temperature changes are very similar to the Earth as well (even though the year, and therefore the seasons, are twice as long on Mars). That means a big drop in temperature in autumn and winter, and a rise again in spring and summer.
The Martian atmosphere, on the other hand, is very different from the Earth’s atmosphere; it is much thinner, and is made up mainly of (about 95 per cent) of carbon dioxide. The planet is also much farther away from Earth than the Sun, so it is much colder there. When winter falls, carbon dioxide from the atmosphere freezes to the ground, especially at higher latitudes.
In 2006 and 2007, geologist Hugh Kieffer and his colleagues suggested, in the spring, that this frozen carbon dioxide would come in – that is, that it would move from ice to gas, without the melt-to-liquid phase between them – locked under moving slabs of surface ice.
As the gas heats up and expands, pressure builds up until the slab breaks, creating a shower for the gas to escape. As it flows toward the wine, the gas sculpts a spider-like system in a Martian surface, carrying the material excavated by it.
Together, the gas and the material are emitted as a high-speed jet. When the ice sheet melts on the last top, what is left is the araneiform.
This hypothetical process, Kieffer noted, is unlike anything seen on Earth; never seen on Mars – we only saw araneiform in satellite images – so McKeown and her team designed an experiment to reproduce the process in a laboratory setting.
They made use of a surprise you see in your kitchen, called the Leidenfrost effect: If water droplets are placed on a surface much hotter than the vaporization point of the water, the droplet will melt (which is why water in a frying pan will be very hot. dancing about it will be like mercury).
Reducing CO2 ice sheet on the sandy sand. (McKeown et al., Sci Rep, 2021)
In a special room with pressure down to the atmosphere of Mars, the team placed a slab of CO2 ice with a single hole drilled through it on a surface covered with small grains of glass that would resemble dirt, or regolith.
As the ice rubbed against the surface, it began to sublimate, visible in the form of gas escaping from the hole. As soon as the team lifted the ice, they found a spider-like false system of channels carved into the glass sand where the gas had flowed over it to escape through the hole.
In fact, the process was so lively, material was thrown around the room, suggesting that sublimation rates on Mars may be in the order of magnitude higher than those on Earth.
The resulting pattern. (McKeown et al., Sci Rep, 2021)
The team repeated the experiment with grains of different sizes to see how different regolith textures affect the result. They found that the better the grain size, the greater the pattern.
In addition, however, this experiment is the first time that scientists have confirmed the existence of a Kieffer hypothesis process. can indeed happens – and great weight is a favor as it relates to the araneiform on Mars.
The findings suggest that geomorphic processes on Mars are still a bit of a mystery up the sleeves, and also that carbon dioxide sublimation could be an explanation for other strange surface features on Mars.
The team hopes that araneiform studies over several years of Mars could help shed more light on the planet’s exciting seasonal processes.
The research was published in Scientific Reports.