Steep Martian slopes reveal structure of underground ice sheets
Scientists using NASA’s Mars Reconnaissance Orbiter (MRO) have located eight sites where thick deposits of ice beneath the Martian surface are exposed in the faces of steep eroding slopes known as scarps. The eight scarps, have slopes as steep as 55 degrees, provide researchers with new information about the internal structure of previously-discovered layered subsurface ice sheets in Mars’s middle latitudes.
The ice was probably deposited long ago in Mars’ past as snow. The deposits are exposed in cross-section as fairly pure water ice covered by a layer one to two yards (or meters) thick of ice-cemented rock and dust. These ice deposits hold clues to the climate of ancient Mars. They may also make it easier than previous thought for future crewed exploration missions to access frozen water.
The team of scientists who found and investigated the eight scarp sites using MRO’s High Resolution Imaging Science Experiment (HiRISE) published their findings in the journal Science on Thursday, January 11. The sites were found in both the northern and southern hemispheres of Mars, at latitudes from approximately 55 to 58 degrees, equivalent on Earth to Scotland or the tip of South America.
The scarps directly expose the edges of vast underground ice sheets previously detected with spectrometers on NASA’s Mars Odyssey orbiter, with ground-penetrating radar instruments on MRO and the European Space Agency’s Mars Express orbiter, and with observations of fresh impact craters that uncover underground ice. In 2008, NASA’s Phoenix lander confirmed and studied buried water ice at 68 degrees latitude, about on-third of the way to the pole from the northernmost of the eight scarp sites.
“The discovery reported today gives us surprising windows where we can see right into these thick underground sheets of ice,” said Shane Byrne of the University of Arizona Lunar and Planetary Laboratory, Tucson, a co-author of the report via an agency-issued release. “It’s like having one of those ant farms where you can see through the glass on the side to learn about what’s usually hidden beneath the ground.”
Researchers still do not know how these particular scarps initially form. Once the buried ice becomes exposed to the Martian atmosphere, a scrap probably grows wider and taller as it “retreats” due to due to sublimation of the ice directly from solid form to water vapor. At some of the sites, the exposed deposit of water ice is more than 100 yards (or meters) thick. An investigation of some of the scarps using MRO’s Compact Reconnaissance Imaging spectrometer for Mars (CRISM) confirmed that the bright material is water ice. Odyssey’s Thermal Emission Imaging System (THEMIS) camera was used to check the surface temperature of the scarps, helping the scientists to determine that they merely observing thin frost covering the surface.
The new findings indicate that underground water ice lies under a thin covering of one to two yards over wide areas. The study notes sites where ice is directly accessible, in regions with less hostile conditions than at Mars’ polar ice caps.
“Astronauts could essentially just go there with a bucket and a shovel and get all the water they need,” Byrne said.
In addition to its potential resource value, the exposed ice also preserves a history of long-term Martian climatic patterns. The tilt of Mars’ axis of rotation varies more than that of Earth’s, over the rhythms of millions of years. The two planets’ tilts are currently about the same. When Mars tilts more, climate conditions may favor the buildup of ice in the middle latitudes.
The new study benefited from coordinated use of multiple science instruments on the Mars orbiters, and the longevity of the MRO and Odyssey missions. While orbital observations will continue, future surface missions could provide more detailed information.
“If you had a mission at one of these sites, sampling the layers going down the scarp, you could get a detailed climate history of Mars,” suggested MRO Deputy Project Scientist Leslie Tamppari of NASA’s Jet Propulsion Laboratory, Pasadena, California. “It’s part of the whole story of what happens to water on Mars over time: Where does it go? When does ice accumulate? When does it recede?”
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.