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A massive reservoir of buried frozen carbon dioxide ice (dry ice) detected by the Mars Reconnaissance Orbiter (MRO) is intimately related to the mass of the red planet’s atmosphere as the planet tilts on its axis, which in turn could affect the stability of liquid water and the frequency and severity of dust storms.
MRO made the detection using its ground penetrating radar instrument, revealing a frozen carbon dioxide ice deposit at Mars’ south pole that occupies a 12,000 cubic kilometre volume and holds 80 percent as much CO2 as today’s atmosphere. Planetary scientists already knew that a small cap of carbon-dioxide ice rested on top of the water ice there, but the newly detected deposit has about 30 times more dry ice than previously estimated.
“The discovery was very surprising to me and many other scientists, although theoretical models had predicted that the CO2 atmosphere would occasionally collapse onto the poles,” Roger Phillips of Southwest Research Institute and deputy team leader for MRO’s Shallow Radar instrument tells Astronomy Now. “To actually find evidence of this is another matter, so we were very careful in our analyses to make sure we got it right.”
Features such as collapse pits, which are known to be caused by dry ice sublimation, suggest that the ice cap is dissipating, adding gas to the martian atmosphere. “There are two types of collapse pits indicating sublimation of the dry ice,” explains Phillips. “There are isolated sublimation pits, up to four kilometres in diameter, and there are linear troughs, along which sublimation collapse pits form. There are also erosional remnants of the CO2 deposit seen in the radar data.”
Phillips adds that if you include this buried deposit, Martian carbon dioxide right now is roughly half frozen and half in the atmosphere, but at other times it can be nearly all frozen or nearly all in the atmosphere. When the dry ice is in its dissipating phase, much of the carbon dioxide enters the planet’s atmosphere, resulting in stronger winds, not only increasing the frequency of dust storms, but also their intensity. They even speculate that conditions might be stable enough for liquid water to exist in some locations on the red planet.
The sublimating dry ice is likely linked to the tilt of Mars’ axis, which affects the amount of sunlight falling onto the polar regions. If Mars’ tilt and orbital parameters act to offer maximum exposure to the summer sunshine at the south pole, this could increase the atmospheric pressure by 75 percent its current level, and modelling suggests that the planet’s atmosphere could change several-fold on the order of 100,000 years or less.
“A tilted Mars with a thicker carbon-dioxide atmosphere causes a greenhouse effect that tries to warm the Martian surface, while thicker and longer-lived polar ice caps try to cool it,” says Robert Haberle of NASA’s Ames Research Center. “Our simulations show the polar caps cool more than the greenhouse warms. Unlike Earth, which has a thick, moist 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.”
Via: ASTRONOMY NOW
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