NASA / JPL-Caltech/University of Rome / Southwest Research Institute
The ribbon colors in this map overlay of the south pole of Mars indicate the thicknesses of the carbon dioxide ice, or dry ice, detected by a radar on NASA's Mars Reconnaissance Orbiter.
updated 4/21/2011 10:30:33 PM ET 2011-04-22T02:30:33

The south pole of Mars has a layer of dry ice that is 30 times thicker than previously thought, a find that suggests the Red Planet may have had more liquid water on its surface in the distant past, scientists say.

While most of the ice at the Martian south pole is frozen water, some of the ice pack is composed of dry ice — frozen carbon dioxide.

A team of scientists used a radar instrument on NASA's Mars Reconnaissance Orbiter to calculate the depth of dry ice deposits. By measuring how long it took for the radar waves to travel through the ice and bounce back to the MRO spacecraft, the researchers determined that the dry ice cache was nearly 2,300 feet (700 meters) thick.

"The volume of the deposit is about the volume of Lake Superior," said study leader Roger Phillips of the Southwest Research Institute.

On a planetary scale, that may not seem like a lot. But dry ice is composed of carbon dioxide, and that quantity has profound implications for the climate of Mars. [Latest Mars Photos from NASA Rovers]

Dry ice on Mars
As on Earth, the tilt of Mars' axis controls the seasons and the temperature. But unlike Earth, which is stabilized by our single large moon, Mars' axis can shift from ramrod straight to a tilt of nearly 60 degrees, a change that influences the southern polar caps.

"When the tilt axis of the planet — the obliquity — is very high, higher than it is now, the carbon dioxide is released into the atmosphere," Phillips told The amount of gas is almost double its present form, he added.

"When the obliquity is low it goes back into the polar caps," Phillips said.

Some of that carbon dioxide is lost through each phase of the cycle, but most of it is retained. It freezes again at the poles, the coldest spots on the planet, until the axis tilts and the cycle begins again.

The cycle can take about 100,000 years to complete, which means that the planet is constantly shifting its carbon dioxide levels. Phillips and his team used the Shallow Subsurface Radar instrument on the MRO spacecraft to measure the Martian dry ice pack.

The research was published online Thursday by the journal Science.

Water on Mars
The low atmospheric pressure of the Red Planet today means that water placed on the surface would almost immediately boil away. However, increased levels of carbon dioxide could have helped support a denser, thicker atmosphere in the past.

NASA / JPL-Caltech /Univ. of Rome / SwRI
This Mars image shows a circular pit within the frozen carbon dioxide (dry ice) pack detected by a radar on a NASA orbiter. The pit is floored with a thin fractured water-ice layer (upper left inset), which is mantled partially by the "Swiss cheese" terrain of the south pole residual cap. Details within the pit are shown in the other insets.

While the result wouldn't be pools of water, there would certainly be more places on the surface that the water wouldn't vaporize as quickly as it does today, researchers said.

"The fact that the atmospheric pressure is doubled and water present would not boil means that there would be more tendencies for gullies to form," Phillips added.

Gullies on Mars were first found by the Mars Global Surveyor in 2000, and provided the first hint that water once flowed across the surface of the Red Planet. Since then, scientists have sought to determine when and how much of the liquid existed in the past.

Water is considered a necessary element for life to exist. However, Phillips emphasized that the increased carbon dioxide in the atmosphere would have had minimal repercussions when it comes to the possibility of life on Mars.

In addition to more surface water, a thicker atmosphere also means more dust storms could have crossed the planet in the past. Today's Martian dust storms are the largest in the solar system, often lasting for months at a time.

Combining increased dust storms with more carbon dioxide could also cause additional, yet-unrealized, changes in the Martian atmosphere, researchers said.

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Photos: The greatest hits from Mars

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  1. The face of Mars

    The Hubble Space Telescope focuses on the full disk of Mars, with a head-on view of a dark feature known as Syrtis Major. Hubble astronomers could make out features as small as 12 miles wide. (AURA / STSCI / NASA) Back to slideshow navigation
  2. Red, white and blue planet

    Two decades before Pathfinder, the Viking 1 lander sent back America's first pictures from the Martian surface. This 1976 picture shows off the lander's U.S. flag and a Bicentennial logo as well as the planet's landscape. (NASA) Back to slideshow navigation
  3. Grand canyon

    This is a composite of Viking orbiter images that shows the Valles Marineris canyon system. The entire system measures more than 1,875 miles long and has an average depth of 5 miles. (NASA) Back to slideshow navigation
  4. Red rover

    A mosaic of eight pictures shows the Pathfinder probe's Sojourner rover just after it rolled off its ramp. At lower right you can see one of the airbags that cushioned Pathfinder's landing on July 4, 1997. (NASA) Back to slideshow navigation
  5. Twin Peaks at their peak

    The Pathfinder probe focuses on Twin Peaks, two hills of modest height on the Martian horizon. Each peak rises about 100 feet above the surrounding rock-littered terrain. (NASA) Back to slideshow navigation
  6. Blue horizon

    A Martian sunset reverses the colors you'd expect on Earth: Most of the sky is colored by reddish dust hanging in the atmosphere, but the scattering of light creates a blue halo around the sun itself. (NASA / JPL) Back to slideshow navigation
  7. Two-faced Mars

    The image at left, captured by a Viking orbiter in the 1970s, sparked speculation that Martians had constructed a facelike monument peering into space. But the sharper image at right, sent back in 1998 by Mars Global Surveyor, spoiled the effect. (NASA) Back to slideshow navigation
  8. Put on a happy face

    The "Happy Face Crater" - officially named Galle Crater - puts a humorous spin on the "Face on Mars" controversy. This image was provided by the Mars Global Surveyor orbiter. (MSSS / NASA) Back to slideshow navigation
  9. A monster of a mountain

    Mars' highest mountain, an inactive volcano dubbed Olympus Mons, rises as high as three Everests and covers roughly the same area as the state of Arizona. Mars Global Surveyor took this wide-angle view. (MSSS / NASA) Back to slideshow navigation
  10. Pockmarked moon

    Mars Global Surveyor snapped this picture of Phobos, the larger of Mars' two potato-shaped moons. Phobos' average width is just 14 miles. The image highlights Phobos' 6-mile-wide Stickney Crater. () Back to slideshow navigation
  11. From Mars with love

    This valentine from Mars, as seen by Mars Global Surveyor, is actually a pit formed by a collapse within a straight-walled trough known in geological terms as a graben. The pit spans 1.4 miles at its widest point. (MSSS / NASA) Back to slideshow navigation
  12. Sandy swirls

    An image taken by Mars Global Surveyor shows a section of the northern sand dunes on Mars' surface. The dunes, composed of dark sand grains, encircle the north polar cap. (JPL / NASA) Back to slideshow navigation
  13. Curls of clouds

    Global Surveyor focuses on a storm system over Mars' north polar region. The north polar ice cap is the white feature at the top center of the frame. Clouds that appear white consist mainly of water ice. Clouds that appear orange or brown contain dust. (MSSS / NASA) Back to slideshow navigation
  14. Swiss cheese

    Global Surveyor captured images of a frost pattern at Mars' south polar ice cap that looks like Swiss cheese. The south polar cap is the only region on the Red Planet to contain such formations. (NASA / JPL / Malin Space Science) Back to slideshow navigation
  15. Purple Planet

    A false-color image from the Opportunity rover, released Feb. 9, 2004, accentuates the differences between a green-looking slab of Martian bedrock and orange-looking spheres of rock. Scientists likened the "spherules" to blueberries embedded within and scattered around muffins of bedrock. The spherules are thought to have been created by the percolation of mineral-laden water through the bedrock layers. (NASA / JPL / Cornell University) Back to slideshow navigation
  16. Dunes of Mars

    A false-color view from NASA's Opportunity rover, released Aug. 6, 2004, shows the dune field at the bottom of Endurance Crater. The bluish tint indicates the presence of hematite-containing spherules ("blueberries") that accumulate on the flat surfaces of the crater floor. (NASA / JPL / Cornell University) Back to slideshow navigation
  17. Alien junkyard

    The Opportunity rover looks at its own heat shield, which was jettisoned during the spacecraft's descent back in January 2004, on Dec. 22, 2004. The main structure from the heat shield is at left, with additional debris and the scar left by the shield's impact to the right. The shadow of the rover's observation mast is visible in the foreground. (NASA / JPL) Back to slideshow navigation
  18. Devil on Mars

    This image shows a mini-whirlwind, also known as a dust devil, scooting across the plains inside Gusev Crater on Mars, as seen from the Spirit rover's hillside vantage point on April 18, 2005. (NASA / JPL) Back to slideshow navigation
  19. Rub al Khali

    The tracks of NASA's Opportunity rover are visible in a panoramic picture of a desolate, sandy stretch of Martian terrain in Meridiani Planum, photographed in May 2005 and released by NASA on July 28. "Rub al Khali" (Arabic for "Empty Quarter") was chosen as the title of this panorama because that is the name of a similarly barren, desolate part of the Saudi Arabian desert on Earth. (NASA / JPL / Cornell University) Back to slideshow navigation
  20. Double moons

    Taking advantage of extra solar energy collected during the day, NASA's Spirit rover spent a night stargazing, photographing the two moons of Mars as they crossed the night sky. The large bright moon is Phobos; the smaller one to its left is Deimos. (NASA / JPL / Cornell / Texas A&M) Back to slideshow navigation
  21. Mars in the round

    A 360-degree panorama shows a stretched-out view of NASA's Spirit rover and its surroundings on the summit of Husband Hill, within Mars' Gusev Crater. The imagery for the panorama was acquired in August, and the picture was released on Dec. 5. (NASA) Back to slideshow navigation
  22. Fossil delta

    Scientifically, perhaps the most important result from use of the Mars Orbiter Camera on NASA's Mars Global Surveyor has been the discovery in November 2003 of a fossil delta located in a crater northeast of Holden Crater. (NASA / JPL / MSSS) Back to slideshow navigation
  23. Underneath the ice

    This view taken in January 2005 shows sharp detail of a scarp at the head of Chasma Boreale, a large trough cut by erosion into the Martian north polar cap and the layered material beneath the ice cap. (NASA / JPL / MSSS) Back to slideshow navigation
  24. Celestial celebration

    Controllers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., cheer on Friday after hearing that Mars Reconnaissance Orbiter successfully made it into orbit around the Red Planet. (Phil McCarten / Reuters) Back to slideshow navigation
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