New clues in Mars' liquid water riddle

NASA said today that new data from the Mars Reconnaissance Orbiter (MRO) has demonstrated that the amount of atmosphere on the Red Planet depends entirely on the tilt of its axis. This is significant, the space agency said, because that axis tilt may well impact the stability of any liquid water that exists on Mars, as well as the frequency and strength of dust storms.

In a release, NASA explained that by employing the MRO's ground-penetrating radar, researchers were able to identify a massive sub-surface deposit of frozen carbon dioxide--dry ice--on Mars' southern pole. "The scientists suspect that much of this carbon dioxide enters the planet's atmosphere and swells the atmosphere's mass when Mars' tilt increases," NASA reported.

With a volume of almost 3,000 cubic miles, the deposit is said to have as much as 80 percent of the carbon dioxide as Mars' entire atmosphere. But so-called "collapse pits cause by dry ice sublimation and other clues suggest the deposit is in a dissipating phase," a process that puts more gas into the planet's atmosphere each year. By contrast, Mars' atmosphere is nearly 95 percent carbon dioxide, while Earth's has less than .04 percent of the substance.

NASA researchers said that they had already been aware of a deposit of dry ice on top of water ice on Mars, but that the sub-surface build-up contains about 30 times as much frozen carbon dioxide as was previously thought.

In addition, they said that at the moment, the planet's build-up of carbon dioxide is half frozen and half in its atmosphere, but that it can sometimes be almost entirely frozen or in the atmosphere--suggesting that as the planet rotates on its axis, the carbon dioxide shifts with it.

"An occasional increase in the atmosphere would strengthen winds, lofting more dust and leading to more frequent and more intense dust storms," NASA said in its release. "Another result is an expanded area on the planet's surface where liquid water could persist without boiling. Modeling based on known variation in the tilt of Mars' axis suggests several-fold changes in the total mass of the planet's atmosphere can happen on time frames of 100,000 years or less."

Ultimately, the effect of these changes can be dramatic. as Robert Haberle, a planetary scientist at NASA Ames' Research Center in Mountain View, California, put it in the release, if Mars is tilted on its axis and has an atmosphere thicker with carbon dioxide, a greenhouse effect is likely that attempts to heat up the surface of the planet. At the same time, if the polar ice caps are thicker and longer-lasting, a cooling effect is likely. "Our simulations show the polar caps cool more than the greenhouse warms," Haberle said in the release. "Unlike Earth, which has a thick, most atmosphere that produces a strong greenhouse effect, Mars' atmosphere is too thin and dry to produce as strong a greenhouse effect as Earth's, even when you double its carbon-dioxide content."