
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

  2. Red, white and blue planet

  3. Grand canyon

  4. Red rover

  5. Twin Peaks at their peak

  6. Blue horizon

  7. Two-faced Mars

  8. Put on a happy face

  9. A monster of a mountain

  10. Pockmarked moon

  11. From Mars with love

  12. Sandy swirls

  13. Curls of clouds

  14. Swiss cheese

  15. Purple Planet

  16. Dunes of Mars

  17. Alien junkyard

  18. Devil on Mars

  19. Rub al Khali

  20. Double moons

  21. Mars in the round

  22. Fossil delta

  23. Underneath the ice

  24. Celestial celebration

  1. Editor's note:
    This image contains graphic content that some viewers may find disturbing.


  2. Editor's note:
    This image contains graphic content that some viewers may find disturbing.


  3. Editor's note:
    This image contains graphic content that some viewers may find disturbing.


  4. Editor's note:
    This image contains graphic content that some viewers may find disturbing.



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