Mars Express radar gauges water quantity around Mars south pole
Thu Mar 15, 2007 at 21:54 UTC
The amount of water trapped in frozen layers over Mars' south polar region is equivalent to a liquid layer about 11 metres deep covering the planet.
This new estimate comes from mapping the thickness of the dusty ice by the Mars Express radar instrument that has made more than 300 virtual slices through layered deposits covering the pole. The radar sees through icy layers to the lower boundary, which in places is as deep as 3.7 kilometres below the surface.
"The south polar layered deposits of Mars cover an area as wide as a big portion of Europe. The amount of water they contain has been estimated before, but never with the level of confidence this radar makes possible," said Dr. Jeffrey Plaut of NASA's Jet Propulsion Laboratory, Pasadena (California), co-Principal Investigator for the radar and lead author of the study.
The instrument, named the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), is also mapping the thickness of similar layered deposits at the north pole of Mars.
"Our radar is doing its job extremely well," said Prof. Giovanni Picardi of the University of Rome 'La Sapienza,' Principal Investigator for the instrument. "MARSIS is showing to be a very powerful tool to probe underneath the Martian surface, and it's showing how our team's goals - such as probing the polar layered deposits - are being successfully achieved," he continued. "Not only MARSIS is providing us with the first ever views of Mars' subsurface at those depths, but the details we are seeing are truly amazing. We are expecting even greater results when we will have concluded an on-going, sophisticated fine-tuning of our data processing methods. These should enable us to understand even better the surface and subsurface composition."
Polar layered deposits hold most of the known water on modern Mars, though other areas of the planet appear to have been very wet at times in the past. Understanding the history and fate of water on Mars is a key to studying whether Mars has ever supported life, because all known life depends on liquid water.
Image Credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team
High resolution image
The upper image is a radargram from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), showing data from the subsurface of Mars in the ice-rich layered deposits that surround the south pole. The lower image shows the position of the ground track (white line) on a topographic map of the area based on Mars Orbiter Laser Altimeter data. The images are 1,250 kilometers (775 miles) wide.
The MARSIS echo trace splits into two traces on the left side of the image, at the point where the ground track crosses from the surrounding plains onto the elevated layered deposits. The upper trace is the echo from the surface of the deposits, while the lower trace is interpreted to be the boundary between the lower surface of the deposits and the underlying material. The strength of the lower echo suggests that the intervening material is nearly pure water ice. Near the image center, the bright lower echo abruptly disappears for unknown reasons. The time delay between the two echoes reaches a maximum of 42 microseconds left of center, corresponding to a thickness of 3.5 kilometers (2.2 miles) of ice. The total elevation difference shown in the topographic map is about 4 kilometers (2.5 miles) between the lowest surface (purple) and the highest (red).
Image Credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team
High resolution image
The upper image is a radargram from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), showing data from the subsurface of Mars in the ice-rich layered deposits that surround the south pole. The lower image shows the position of the ground track (white line) on a topographic map of the area based on Mars Orbiter Laser Altimeter data. The images are 1,580 kilometers (980 miles) wide.
Near the image center, several bright bands between the echo traces are likely caused by interaction of the radar waves with internal layers of the deposits. The time delay between the upper and lower traces in the banded area is 20 microseconds, corresponding to a thickness of 1.6 kilometers (1.0 miles) of ice. The total elevation difference shown in the topographic map is about 3 kilometers (2.5 miles) between the lowest surface (dark blue) and the highest (yellow).
Image Credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS
High resolution image
This map shows the thickness of the south polar layered deposits of Mars, an ice-rich geologic unit that was probed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). The MARSIS radar is an instrument on the European Space Agency's Mars Express orbiter. The thickness of the layered deposits was determined by measuring the time delay between radar echoes from the surface and those from the lower boundary, or "bed", of the deposits. The radar data indicate that the deposit, larger than Texas in area, is more than 3.7 kilometers (2.3 miles) thick in places, and that the material consists of nearly pure water ice with only a small component of dust.
The map was generated by comparing the elevation of the bed as determined by MARSIS with the high-resolution map of surface topography obtained by the Mars Orbiter Laser Altimeter aboard NASA's Mars Global Surveyor orbiter. The thickness of the layered deposits is shown by colors, with purple representing the thinnest areas, and red the thickest. The total volume of ice in the layered deposits is equivalent to a water layer 11 meters (36 feet) deep, if spread evenly across the planet. The boundary of the layered deposits was mapped by scientists from the U.S. Geological Survey. The dark circle in the upper center is the area poleward of 87 degrees south latitude, where MARSIS data cannot be collected. The map covers an area 1,670 by 1,800 kilometers (1,035 by 1,115 miles).
Image Credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS
High resolution image
This map shows the topography of the south polar region of Mars, including topography buried by thick deposits of icy material. The map is a combination of surface elevation data acquired by the Mars Orbiter Laser Altimeter aboard NASA's Mars Global Surveyor orbiter, and subsurface elevation data acquired by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) aboard the European Space Agency's Mars Express orbiter.
The black line shows the boundary of the south polar layered deposits, an ice-rich geologic unit that was probed by MARSIS. Elevation values within the black outline, as measured by MARSIS, show the topography at the boundary between the layered deposits and the underlying material, an interface known as the "bed" of the deposits. The elevation of the terrain is shown by colors, with purple and blue representing the lowest areas, and orange and red the highest. The total range of elevation shown is about 5 kilometers (3 miles). The radar data reveal previously undetected features of topography of the bed, including depressions as deep as 1 kilometer (0.6 miles) shown in purple in the near-polar region. The boundary of the layered deposits was mapped by scientists from the U.S. Geological Survey. The dark circle in the upper center is the area poleward of 87 degrees south latitude, where MARSIS data cannot be collected. The map covers an area 1,670 by 1,800 kilometers (1,035 by 1,115 miles).
Image Credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS
High resolution image
This map shows the topography of the south polar region of Mars. The data were collected by the Mars Orbiter Laser Altimeter aboard NASA's Mars Global Surveyor orbiter between 1997 and 2001. The elevation of the terrain is shown by colors, with purple and blue representing the lowest areas, and orange and red the highest. The total range of elevation shown is about 5 kilometers (3 miles). The black line shows the boundary of the south polar layered deposits, an ice-rich geologic unit that was probed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) aboard the European Space Agency's Mars Express orbiter.
The radar data indicate that the deposit is more than 3.7 kilometers (2.3 miles) thick in places, and that the material consists of nearly pure water ice, with only a small component of dust. The MARSIS team also determined that the total volume of ice in the layered deposits is equivalent to a water layer 11 meters (36 feet) deep, if spread evenly across the planet. The boundary of the layered deposits was mapped by scientists from the U.S. Geological Survey. The dark circle in the upper center is the area poleward of 87 degrees south latitude, where MARSIS data cannot be collected. The image covers an area 1,670 by 1,800 kilometers (1,035 by 1,115 miles).
Plaut, Picardi and 22 other researchers report analysis of the Mars Express radar instrument's south polar observations in the online edition of the journal Science this week.
The polar layered deposits extend beyond and beneath a polar cap of bright-white frozen carbon dioxide and water at Mars' south pole. Dust darkens many of the layers. However, the strength of the echo that the radar receives from the rocky surface underneath the layered deposits suggests the composition of the layered deposits is at least 90 percent frozen water. One area with an especially bright reflection from the base of the deposits puzzles researchers. It resembles what a thin layer of liquid water might look like to the radar instrument, but the conditions are so cold that the presence of melted water is deemed highly unlikely.
Detecting the shape of the ground surface beneath the ice deposits provides information about even deeper structure of Mars. "We didn't really know where the bottom of the deposit was," Plaut said. "We can see now that the crust has not been depressed by the weight of the ice as it would be on the Earth. The crust and upper mantle of Mars are stiffer than the Earth's, probably because the interior of Mars is so much colder."
European Space Agency News Release
