February 10, 2025

Sofia McGrath

11th Grade

The Young Women's Leadership School of Queens

Introduction

Mars has often been a location of mystery and considerable interest as a site of significant scientific value.  Mars is prevalently explored scientifically, from looking for biosignatures of past life to determining the potential of Mars to sustain life in the future. In the past years, NASA discovered unusual spider-like shapes on Mars' southern hemisphere terrain. These formations that once perplexed scientists now have an explanation due to a theory confirmed by extensive testing. The experiments have resulted in new insights that have contributed to solving the mystery of Mars’ “spiders.”

Mars’ “spiders”-officially known as araneiform terrain- were first discovered in 2003 from images by orbiters, and have prompted considerable fascination. Measuring 45 meters long and 1 kilometer wide with the possibility of hundreds of legs or branches, its geologic features were a marvel. However, scientists had a leading theory that its formation was in relation to carbon dioxide. This theory was supported by the Kieffer model, a widely accepted hypothesized conceptual model that explains the appearance of the spider-like terrain through CO2 ice sublimation (conversion from solid to gas) as Mars' seasons change. However, few verifiable observations have been made in the laboratory. Therefore, although promising, this theory needed to be tested. 

Methodology

To test this theory, researchers at NASA’s Jet Propulsion Laboratory recreated this spider-like terrain by simulating Mars’ environment in the lab, with similar temperature and air pressure conditions. According to planetary geomorphologist Lauren Mc Keown, recreating these conditions was the most challenging part. Scientists utilized a liquid nitrogen-cooled test chamber named the “Dirty Under Vacuum Simulation Testbed for Icy Environments”-otherwise known as DUSTIE.  DUSTIE was used to simulate the carbon dioxide ice on Mars' south pole by cooling and condensing carbon dioxide gas to form carbon dioxide ice over 3 to 5 hours. This process was time-consuming as it took many attempts to mimic the thickness and translucency of Mars ice.  They then heated the ice until it cracked, thus releasing a plume of CO2 gas and leaving behind the familiar araneiform terrain. For scientists like Mc Keown-who had spent five years working towards this goal- this successful recreation was exhilarating. The experiments performed were crucial to learn more about these unusual features and gain insights into Mars’ geology.

Explanation

Thanks to these experiments, scientists have confirmed that during the springtime in Mars when the sun heats up the carbon dioxide ice formed over the winter months, it turns it into its gaseous state. This process is called sublimation. The CO2 eventually accumulates, and the pressure intensifies until it breaks through the ice. High pressure ejects the sediments and materials from the underlying soil to the surface. The spider-like geologic features are from the aftermath of the eruption. While these discoveries supported the leading theory and the Kieffer model, there was an unexpected discovery: before cracking open, ice formed between the grains of the simulant(JPL, 2024). This event could explain the zig-zag-like shape of the terrain’s legs(Baker, 2024).  This discovery conveys one aspect of the significance of such experiments as the conceptual model did not reflect all the processes that occurred in the lab. 

 Future Investigations

Scientists have confirmed the reason why araneiform terrain forms. However, more investigations are needed to understand this terrain further. For example, scientists have yet to discover the reason this terrain only appears on some locations of Mars while not others. This question is one of many that the residents of the Jet Propulsion Laboratory plan to investigate.  It is evident that there are more mysteries of  Mars’ “spiders” that need addressing.