Newly discovered layers of ice buried a mile below the north pole of Mars are remnants of ancient polar ice sheets and could be one of the largest reservoirs of water on the planet, according to scientists at the University of Texas at Austin. the University of Arizona.
The team made the discovery using measurements collected by Surface Radar (SHARAD) at NASA's Mars Reconnaissance Orbiter (MRO). SHARAD emits radar waves that can penetrate up to a mile and a half below the surface of Mars.
The findings, published on May 22 in. Geophysical research letters, they are important because ice sheets are a record of past climate on Mars in the same way that tree rings are a record of past climate on Earth. The study of the geometry and composition of these layers could tell scientists if weather conditions were earlier favorable for life, the researchers said. The team found layers of sand and ice that were up to 90% water in some places.
If melted, the newly discovered polar ice would be equivalent to a global layer of water around Mars with a depth of at least 1.5 meters (5 feet).
"We did not expect to find so much water ice here," said lead author Stefano Nerozzi, a graduate research assistant at the University of Texas Geophysics Institute (UTIG) who is completing his Ph.D. at the Jackson School of Geosciences. "That probably makes it the third largest reservoir of water on Mars after the polar ice caps."
The findings were corroborated by an independent study that used severity data instead of radar, led by researchers at Johns Hopkins University. Nerozzi was co-author. The works have been published simultaneously in Geophysical research letters.
The authors believe that the layers formed when ice accumulated at the poles during the ice ages spent on Mars. Every time the planet warmed up, a remnant of the ice sheets was covered with sand, which protected the ice from solar radiation and prevented it from dissipating into the atmosphere.
Scientists have long known about the glacial events on Mars, which are driven by variations in the planet's orbit and tilt. During periods of approximately 50,000 years, Mars tilts toward the sun before gradually returning to a vertical position, like a tumbling top. When the planet rotates in a vertical position, the equator faces the sun, which allows the polar caps to grow. As the planet tilts, the layers of ice retreat, perhaps disappearing completely.
Until now, scientists thought that the old ice caps had been lost. The document shows that, in fact, important remains of layers of ice have survived beneath the surface of the planet, trapped in alternating bands of ice and sand, like layers in a cake.
Co-author Jack Holt, a professor at the Lunar and Planetary Laboratory at the University of Arizona, said the study provides new and important insights into the exchange of water ice between the poles and mid-latitudes, where his research group previously confirmed the presence of extended glaciers, also using the SHARAD instrument.
"Surprisingly, the total volume of water enclosed in these buried polar deposits is approximately the same as all the water ice that is known to exist in glaciers and ice layers buried at the lower latitudes of Mars, and they have approximately same age, "he said. .
Holt, who was a UTIG scientist and a research professor for 19 years before joining the University of Arizona in 2018, has been an assistant researcher with SHARAD since the spacecraft arrived on Mars in 2006.
Nerozzi said studying this record of past polar glaciations could help determine if Mars was ever habitable.
"Understanding the amount of water available globally compared to what is trapped at the poles is important if you are going to have liquid water on Mars," Nerozzi said. "You can have all the right conditions for life, but if most of the water is enclosed in the poles, then it is difficult to have sufficient quantities of liquid water near the equator."
The study was supported by a grant from NASA's Mars Data Analysis Program and the MRO Project Office at the Chorro Jet Propulsion Laboratory. SHARAD was provided to NASA's MRO mission by the Italian Space Agency.
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