Gullies on Mars Give Way to Dreams of Snowboarding in Space
This image from the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter is an example "linear gullies" formed by dry ice thawing across the planet's sand dunes. Courtesy NASA/JPL-Caltech/University of Arizona.
Mars' surface is streaked with furrows and ditches across its rusty red soil, mimicking our planet's river plains. But unlike Earth, Mars has no surface rivers or streams that would leave such marks.
Serina Diniega, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead author of a report published online in the journal Icarus, determined these signature gullies on its red sand dunes are a result of cascades of dry ice running across the planet's surface every spring.
"I have always dreamed of going to Mars," Diniega said in a post on NASA's website. "Now I dream of snowboarding down a Martian sand dune on a block of dry ice."
"To find out if frozen carbon dioxide left tracks on Mars, scientists grabbed a bag of dry ice and took a road trip. Courtesy NASA/JPL-Caltech
At first glance, the channels look like riverbeds on Earth. But when rivers on Earth reach their end, they leave a plain of silt and debris. Images from Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment camera show linear gullies on Mars' surface end abruptly.
The HiRISE images also showed the red dunes covered by carbon-dioxide frost during the Martian winter. By comparing photos from different seasons, researchers determined that the grooves must have formed during early spring. Some images revealed bright objects in the gullies, which researchers determined was dry ice.
Dry ice is carbon dioxide in its solid form, something that doesn't naturally form on Earth's surface, Diniega said. But it's abundant on Mars, where a CO2-rich atmosphere produces snowbanks of frozen carbon dioxide, not water. Candice Hansen posited that as the dry ice thaws into a gas each the spring, it cuts the linear gullies as it slides down the hillsides before dissipating into the atmosphere.
To test this theory, Hansen and Diniega took blocks of dry ice -- only a few inches thick -- from a supermarket, along with water ice and wooden blocks, out to the Coral Pink Sand Dunes in Utah. Carbon dioxide gas from the thawing dry ice maintained a lubricating layer under the slab, turning the blocks into miniature hovercraft. As the slabs of dry ice glided down the slopes, the gaseous bottom layer pushed sand into little valleys. Their water ice blocks simply melted into a puddle, leaving only wet sand behind, and the wooden blocks didn't move at all.
Diniega and her JPL colleagues tested their theory again on the Kelso Dunes in southern California. Their experiments drew a crowd of local teens camping in the park, she said. Soon, scientists and campers were cheering as the carbon dioxide blocks schussed down the sand.
The dry ice blocks spotted in the Martian gullies are four to seven feet across, Diniega said. With a big enough block, and proper insulation to protect the skin from burns, a person could snowboard down the dunes on Mars -- a sport she would love to see, she joked.
Ultimately, this shows that while Mars and Earth have a lot in common, we have a lot left to learn about our neighboring planet, she said.
"We see things on Mars that look very Earth-like and that's very exciting. We want to travel to Mars and it's our closest planet," Diniega said. "It's a nice reminder that Mars is a very different planet and it has its own mysteries."