Scientists have long been intrigued by the spider-shaped geologic features found in the southern hemisphere of Mars, known as araneiform terrain. These distinctive formations, stretching over half a mile and resembling intricate legs, have puzzled researchers for years. Now, a series of experiments conducted at NASA's Jet Propulsion Laboratory (JPL) has provided insights into the formation process of these enigmatic structures, confirming the role of carbon dioxide in their creation.

The experiments, detailed in a new paper published in The Planetary Science Journal, aimed to emulate the extreme conditions present on the Martian polar surface, including low air pressure and subfreezing temperatures. To achieve this, scientists used a liquid-nitrogen-cooled test chamber at JPL called the Dirty Under-vacuum Simulation Testbed for Icy Environments (DUSTIE).

Using Martian soil simulant stored in a container submerged in a liquid nitrogen bath, researchers recreated the conditions prevalent in Mars' southern hemisphere. Carbon dioxide gas was introduced into the chamber, which gradually condensed into ice over several hours. Through controlled heating, the ice cracked, leading to the eruption of carbon dioxide gas and the expulsion of dark dust and sand particles from the simulant, resembling the plumes observed on Mars.

"The spiders are strange, beautiful geologic features in their own right," said Lauren McKeown of NASA's JPL. "These experiments will help tune our models for how they form." The study aligns with the Kieffer model, which suggests that sunlight passing through transparent carbon dioxide ice slabs heats the underlying soil. The dark soil absorbs the heat, causing the ice closest to it to sublimate directly into carbon dioxide gas. As the gas builds pressure, it cracks the ice, allowing the gas and entrained particles to escape.

Interestingly, the experiments also revealed an alternative process not predicted by the Kieffer model. Ice formation between the soil grains led to the cracking of the simulant, potentially explaining the "cracked" appearance of some spider-like formations on Mars. This discovery illustrates the intricate complexities of Martian processes, highlighting that nature may be messier than initially envisioned.

The successful recreation of these formation processes in a lab setting paves the way for further investigations. Future experiments aim to incorporate simulated sunlight from above to better understand the conditions under which the plumes and soil ejections occur. Additionally, scientists hope to unravel the mysteries surrounding the distribution of these formations on Mars and their relationship to long-ago climate changes.

While laboratory experiments provide valuable insights, the real spiders on Mars remain largely inaccessible to rovers. Both the Curiosity and Perseverance rovers are exploring different regions of the Red Planet, far from the southern hemisphere where the spider formations are concentrated. The Phoenix mission, which landed in the northern hemisphere, provided limited observations before succumbing to the extreme cold and limited sunlight.

As scientists continue to unlock the secrets of these intriguing spider-shaped formations, the experiments conducted at NASA's JPL offer a deeper understanding of the role played by carbon dioxide in shaping the Martian landscape. These findings not only contribute to the knowledge of Mars' geological processes but also provide a glimpse into the planet's past and its potential as a window into ancient Martian climates.