Giant spider-like features called araneiform terrain appear to gouge Mars’ surface near its poles. Since they were first discovered in 2000, scientists have been refining their models to understand how these strange features arise on the red planet.
Planetary Science Institute Senior Scientist Candice Hansen is a co-author on a new paper published in the Planetary Science Journal that validates the prevailing model with laboratory experiments done on Earth.
After studying images from the Mars Observer Camera, geophysicist Hugh Kieffer published a series of papers throughout the 2000s that describe the mechanism for creating araneiform terrain in the Martian south polar region. He suggested that in spring, sunlight shines through a thick, transparent sheet of carbon dioxide ice and warms the dark sand below. The heat transforms the ice at the base from solid to gas, creating a buildup of pressure. Eventually, the building pressure breaks the ice, and as the carbon dioxide gas rushes to escape, it blasts sand along with it, carving the Martian surface, resulting in the spider-like terrain.
To confirm the models for araneiform formation, the team – which was led by Lauren Mc Keown of NASA’s Jet Propulsion Laboratory – had to recreate the environmental conditions of the red planet in an Earth-bound laboratory setting.
To a wine barrel-size liquid-nitrogen-cooled test chamber – called the Dirty Under-vacuum Simulation Testbed for Icy Environments, or DUSTIE – the team added a simulated Martian soil and carbon dioxide gas. They cooled the chamber to minus 301 degrees Fahrenheit and dramatically reduced the air pressure. They then heated the faux soil from the bottom until they observed a gust of carbon dioxide gas breaking through the ice.
“Our work confirmed much of the Kieffer model,” Hansen said. “Plumes were generated in the lab for the first time, ejecting gas and dust.”
“I shrieked with excitement when I saw the plume,” Mc Keown said. “Candy (Hansen) is a great inspiration and role model to me, and she has been diligently hunting for plumes on Mars for years, but they are elusive. I was so excited to share the news with her that we had recreated Kieffer model plumes in the lab for the first time.”
There was also an unexpected finding.
Ice formed between the grains of the simulated soil, then cracked it open. This alternative process might explain why some spiders on Mars have a more cracked appearance. Whether this happens or not seems dependent on the size of soil grains and how embedded water ice is underground.
Future experiments aim to be more realistic by making changes such as shining sunlight on the sample to warm the soil rather than using a heater. As laboratory experiments more closely match reality, so too can scientific understanding of these mysterious features.
