NASA researchers have succeeded in recreating the strange "spider-like" formations observed on the surface of Mars, offering the most concrete explanation to date for these peculiar features.
The formations, called araneiforms, appear in the southern polar regions of the planet and have long puzzled scientists and the public alike. These formations are not the result of any living organisms but are created through natural geological processes unique to the Martian environment. Understanding these features not only unravels a long-standing Martian mystery but also offers insights into the broader mechanics of the planet’s surface.
What Exactly Are the ‘Spiders’ on Mars?
The "spiders" on Mars, scientifically known as araneiforms, are dark, web-like troughs that form across the Martian surface, particularly in the southern polar region during the Martian spring. These formations, first noticed in satellite images, resemble intricate tendrils spreading across the planet’s dusty landscape. Although they look eerie and alive in images, these formations are purely geological. The term "spiders" was coined because of the visual similarity to the long-legged creatures on Earth, but in reality, they are the result of interactions between carbon dioxide ice and the Martian soil, a process that doesn't occur naturally on Earth.
The leading explanation for these structures comes from the Kieffer model, proposed in 2006 by geophysicist Hugh Kieffer. According to this model, during the freezing Martian winter, carbon dioxide from the atmosphere freezes on the surface, creating a solid layer of ice. When spring arrives, sunlight penetrates the ice, causing the carbon dioxide underneath to heat up and sublimate directly into gas, since carbon dioxide doesn’t have a liquid phase under Martian conditions. The gas builds up beneath the ice, creating pressure. Eventually, this pressure becomes too great, and the gas bursts through the ice, carrying dust and debris with it, creating the distinct, spider-like patterns. "These spiders are strange, beautiful geologic features in their own right," says Lauren Mc Keown, a planetary scientist at NASA’s Jet Propulsion Laboratory.
Laboratory Confirmation of the Kieffer Model
To verify this model, a team of researchers from NASA’s Jet Propulsion Laboratory (JPL) conducted a series of experiments designed to replicate the extreme Martian conditions in a controlled environment. The team used a specialized chamber known as the Dirty Under-vacuum Simulation Testbed for Icy Environments (DUSTIE) to mimic the cold temperatures and low-pressure environment found on Mars. They placed a simulant of Martian regolith—a mixture designed to mimic the soil composition of Mars—inside the chamber, cooling it with liquid nitrogen. Then, they introduced carbon dioxide into the chamber, which condensed and froze into a slab of ice, simulating the Martian winter.
The next step was crucial: they gradually warmed the chamber to simulate the coming of the Martian spring. As expected, the ice began to sublime from beneath, just as the Kieffer model predicted. After multiple attempts and adjustments to the experimental conditions, the researchers observed a sudden burst of gas escaping through cracks in the ice, carrying the regolith with it and creating patterns remarkably similar to the araneiforms seen on Mars. "It was late on a Friday evening, and the lab manager burst in after hearing me shrieking," Mc Keown recalled. "She thought there had been an accident."
This experiment not only confirmed that the gas pressure buildup beneath the carbon dioxide ice was responsible for the spider-like formations but also revealed an unexpected twist: the ice appeared to form within the dirt layer, rather than between the dirt and the ice, as initially theorized. This subtle difference may lead to new refinements in how scientists understand the process. "Our plumes created crack morphologies that appeared to be driven by sublimation of interstitial ice within the regolith, rather than scouring of gas within the substrate-frost interface," the research team reported. This nuance adds complexity to the original Kieffer model and may help explain other surface features on Mars.
Broader Implications for Understanding Mars' Surface
The successful recreation of araneiforms in the lab not only provides definitive evidence that the Kieffer model is correct but also suggests that similar processes might be responsible for other Martian surface features. For instance, formations such as polygonal terrains and dendritic troughs could be caused by similar sublimation processes involving carbon dioxide ice. This discovery opens up new avenues for researchers to explore how seasonal changes on Mars drive its surface evolution, particularly in the polar regions.
This finding has significant implications for understanding the broader dynamics of Mars' surface geology. The study’s results also highlight the unique role that carbon dioxide plays in shaping Martian landscapes, a role that differs markedly from processes observed on Earth. On Mars, the absence of water-driven erosion processes we are familiar with means that features like araneiforms are likely shaped by the seasonal cycling of carbon dioxide, which acts as the dominant erosive agent in the planet’s cold, dry environment.
The researchers involved in the study are keen to refine their models further and conduct more experiments to better understand the formation of other seasonal features. "We conclude that the erosion by active CO2 jets might be more complex than the original Kieffer model describes, and beyond spiders, it may contribute to the formation of other typical Martian morphologies like polygonal terrains," the team explained in their paper, published in The Planetary Science Journal. Future studies will likely focus on exploring these connections and refining our understanding of how active CO2 jets interact with the Martian surface.
A step Forward in Understanding Mars
The ability to reproduce spider-like features on Mars in a controlled laboratory environment represents a significant step forward in planetary science. It demonstrates how complex environmental processes can create the strange and beautiful formations observed on the red planet, while also shedding light on the fundamental geological mechanisms at play. As NASA and other space agencies continue their exploration of Mars, these findings will play a key role in interpreting the planet’s surface features and understanding its seasonal dynamics.
This breakthrough also highlights the importance of continued experimentation and model refinement in planetary science. As Mc Keown and her team noted, while the experiments support the Kieffer model, they also point to unexpected complexities in how these features form. Understanding these complexities could provide further insights into the evolution of the Martian surface and guide future missions to Mars as scientists continue to unravel the mysteries of the red planet.