Martian “spiders” are small, dark, spider-shaped formations up to 1 km (0.6 miles) in diameter. The leading theory is that they form when spring sunlight hits a layer of carbon dioxide that builds up during the dark winter months. In a new experiment, a team of NASA scientists has recreated these formation processes for the first time, simulating Martian temperatures and air pressure.
Examples of “Keefer Zoo” features proposed to have formed by seasonal CO2 sublimation dynamics on Mars: (a) a “skinny” spider within layered deposits in Antarctica, (b) a dark spot on a layer of translucent CO2 slab ice covering a group of “fat” spiders in an “Inca city” on Mars, (c) a “fried egg” showing a ring of dark dust surrounded by a bright halo, (d) patterned ground within high Antarctic latitudes with dark directional fans and some bright white fans indicating wind direction, (e) a bright halo surrounding a Swiss cheese depression, (f) a “lacey topography”, a type of patterned ground suggested to be polygonal patterned ground that was later scraped and eroded by surface-flowing CO2 gas from the Keefer model. Image credit: HiRISE/NASA Jet Propulsion Laboratory/University of Arizona.
Today, Mars is a dynamic planet with a rich variety of surface changes, despite its thin atmosphere and cold climate.
In winter, most of Mars' mostly carbon dioxide atmosphere accumulates on the surface as frost.
In spring, it sublimates and takes on forms never seen on Earth.
These include dark Dalmatian spots, directional alluvial fans, “fried eggs”, grooves which may have dark finger-like flows or light “halos” in spring, dendritic “spiders”, sand grooves in active dunes and growing dendritic valleys.
These features have been detected in the loose material around the Antarctic and in the inter-dune material towards the mid-Antarctic latitudes, although some smaller phenomena have also been detected in the Arctic.
Many of these features make up the so-called “Kiefer zoo,” or collection of surface expressions. Explained It was first published in 2003 and was proposed to be produced by the solid-state greenhouse effect.
“In the Kiefer model, sunlight penetrates a translucent ice sheet in spring, trapping thermal radiation and heating the topsoil beneath the ice, causing the impermeable sheet to sublime from beneath,” explained Dr. Lauren McKeown of NASA's Jet Propulsion Laboratory and her colleagues.
“Through this process, the spiders are thought to be caused by high-velocity gases scraping away topsoil beneath the ice sheet, littering the ice surface with fan and patchy variations that are then deposited by dust and gas plumes.”
The study authors were able to create a complete cycle of the Kiefer model in the lab and confirm the formation of several types of Kiefer zookeeper features.
“The greatest challenge in conducting the experiment was replicating the conditions found on the polar surface of Mars, namely the extremely low air pressure and temperatures of minus 185 degrees Celsius (minus 301 degrees Fahrenheit),” the researchers said.
“To do this, we used a liquid nitrogen-cooled test chamber, the Dirty Under Vacuum Simulation Chamber for Icy Environments (DUSTIE).”
“In our experiments, we cooled a Martian soil simulant in a container submerged in a bath of liquid nitrogen.”
“We placed it in the Dusty Chamber, where the air pressure was lowered to the same as in the southern hemisphere of Mars.”
“Carbon dioxide gas was then released into the chamber, where it condensed from the gas into ice over a period of three to five hours.”
“It took a lot of trial and error before we found the right conditions to make the ice thick and clear enough for the experiment to work.”
“Once we have ice with the right properties, we place a heater in the chamber underneath the simulant to heat it up and crack the ice.”
“We were thrilled when we finally saw plumes of carbon dioxide gas coming out of the powdered simulant.”
a paper The explanation for these experiments is Planetary Science Journal.
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Lauren E. McKeon others2024. Laboratory-scale investigation of the Kiefer Model of Mars. Planet Science Journal 5, 195;doi:10.3847/PSJ/ad67c8
Source: www.sci.news
