Newly discovered layers of ice buried a mile beneath Mars’ north pole are the remnants of ancient polar ice sheets, report researchers.
It could be one of the largest water reservoirs on the planet, according to new research.
The team made the discovery using measurements that the Shallow Radar (SHARAD) on NASA’s Mars Reconnaissance Orbiter gathered. SHARAD emits radar waves that can penetrate up to a mile and a half beneath the surface of Mars.
The findings are important because the layers of ice are a record of past climate on Mars in much the same way that tree rings are a record of past climate on Earth. Studying the geometry and composition of these layers could tell scientists whether climate conditions were previously favorable for life, researchers say. The team found layers of sand and ice that were as much as 90 percent water in some places.
If melted, the newly discovered polar ice would be equivalent to a global layer of water around Mars at least 1.5 meters (5 feet) deep.
“We didn’t expect to find this much water ice here,” says lead author Stefano Nerozzi, a graduate research assistant at the University of Texas Institute for Geophysics who is completing his PhD at the Jackson School of Geosciences. “That likely makes it the third largest water reservoir on Mars after the polar ice caps.”
Researchers at Johns Hopkins University corroborated the findings in an independent study the findings using gravity data instead of radar. The first and second papers both appear in Geophysical Research Letters.
The authors think that the layers formed when ice accumulated at the poles during past ice ages on Mars. Each time the planet warmed, sand covered a remnant of the ice caps, which protected the ice from solar radiation and prevented it from dissipating into the atmosphere.
Scientists have long known about glacial events on Mars, which are driven by variations in the planet’s orbit and tilt. Over periods of about 50,000 years, Mars leans toward the sun before gradually returning to an upright position, like a wobbling spinning top. When the planet spins upright, the equator faces the sun, allowing the polar ice caps to grow. As the planet tilts, the ice caps retreat, perhaps vanishing entirely.
Until now, scientists thought that the ancient ice caps were lost. The paper shows that in fact significant ice sheet remnants have survived under the planet’s surface, trapped in alternating bands of ice and sand, like layers on a cake.
Coauthor Jack Holt, a professor at the Lunar & Planetary Laboratory of the University of Arizona, says that the study provides new, important insights into the exchange of water ice between the poles and the midlatitudes, where his research group previously confirmed the presence of widespread glaciers, also using the SHARAD instrument.
“Surprisingly, the total volume of water locked up in these buried polar deposits is roughly the same as all the water ice known to exist in glaciers and buried ice layers at lower latitudes on Mars, and they are approximately the same age,” he says.
Nerozzi says that studying this record of past polar glaciation could help determine whether Mars was ever habitable.
“Understanding how much water was available globally versus what’s trapped in the poles is important if you’re going to have liquid water on Mars,” Nerozzi says. “You can have all the right conditions for life, but if most of the water is locked up at the poles, then it becomes difficult to have sufficient amounts of liquid water near the equator.”
Support for the study came from a grant from the NASA Mars Data Analysis Program and the MRO Project Office at the Jet Propulsion Laboratory. The Italian Space Agency provided SHARAD to NASA’s MRO mission.
Source: UT Austin