Each spring, when the winter frost departs, the bulbous bodies and sprawling legs of “spiders” appear across Mars’ southern hemisphere. They’re known as araneiform terrain, and scientists at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, recently recreated the formations in a vacuum on Earth to better understand how they form and what they can tell us about the martian climate.
Related: The science behind the ‘spiders’ on Mars and the Inca City
Forming araneiform terrain
Since researchers discovered araneiform terrain in 2003 using NASA’s Mars Global Surveyor orbiter, they have believed that the terrain — along with similar patterns, knowns as halos, fried eggs, or lace — form via a process called the Kieffer model.
Each winter, carbon dioxide condenses out of the atmosphere onto the martian regolith, forming slabs of translucent ice. The Kieffer model says that solar radiation can pass through the ice and heat the rocky ground underneath, which in turn releases infrared radiation in a kind of greenhouse effect, heating the ice from the bottom up and causing it to sublimate (turning directly to a gas, like dry ice). This causes a buildup of pressure until the slab explodes open, forming cracks as the gas expands and escapes. Plumes of dust and debris erupt outward during this process, littering the surrounding area. The ground grows scarred from these interactions, leaving troughs in patterns like the spiders.
Making Mars in the lab
Despite their confidence in this theory, scientists have been unable to prove it until now. A new study, published Sep. 11 in the Planetary Science Journal, tested whether the Kieffer model was the cause for these springtime changes. Within a barrel-sized chamber called the Dirty Under-vacuum Simulation Testbed for Icy Environments (DUSTIE), a team at JPL was able to drop the temperature to minus 301 degrees Fahrenheit (minus 185 degrees Celsius) at very low air pressure to mimic the martian atmosphere for the experiment.
