Scientists have donned their Sherlock Holmes caps to solve a mystery that's been running for decades – the origins of a huge, layered expanse of CO2 ice and water ice at the south pole of Mars, and its link to the CO2 in the Martian atmosphere.
科學家們戴上夏洛克·福爾摩斯的帽子，解開了一個持續了幾十年的謎團-火星南極一大片層次分明的二氧化碳冰和水冰的起源，以及它與火星大氣中二氧化碳的聯繫。
One leading hypothesis is that these layers were packed on top of each other as the axis of Mars tilts towards and away from the Sun, and simulation models published in a new study back up that idea.
一個主要的假設是，當火星的軸線朝向太陽和遠離太陽時，這些層相互堆積在一起，在一項新的研究中公佈的模擬模型支持了這一觀點。
The ice cap in question is around a kilometre (two-thirds of a mile) deep, and is thought to hold as much CO2 as there is in the entirety of the Martian atmosphere today, and a combination of factors have produced this unusual layered pattern.
所討論的冰蓋大約有一公里(三分之二英里)深，據認為其容納的二氧化碳與今天整個火星大氣中的二氧化碳一樣多，並且是多種因素的組合導致了這種不尋常的分層模式。
"Usually, when you run a model, you don't expect the results to match so closely to what you observe," says Peter Buhler, a planetary scientist at NASA's Jet Propulsion Laboratory.
美國宇航局噴氣推進實驗室的行星科學家彼得·布勒說：“通常，當你運行一個模型時，你不會期望結果與你觀察到的結果如此接近。”
"But the thickness of the layers, as determined by the model, matches beautifully with radar measurements from orbiting satellites."
“但是由模型確定的層厚度與軌道衛星的雷達測量結果非常吻合。”
What makes the ice cap at the south pole so strange is that it shouldn't really be there – water ice is more thermally stable and darker than CO2 ice, so scientists would expect CO2 ice to destabilise when trapped under water ice.
南極的冰帽之所以如此奇怪，是因為它不應該真的存在-水冰比二氧化碳冰更熱穩定，顏色更深，所以科學家們預計二氧化碳冰在被困在水冰下時會變得不穩定。
Three factors have stopped that from happening, according to the new model: the changing tilt of Mars as it orbits the Sun, the differences in the way that these two types of ice reflect sunlight, and the change in atmospheric pressure that happens when CO2 ice turns into a gas.
根據新模型，有三個因素阻止了這種情況的發生：火星繞太陽運行時的傾斜變化，這兩種冰反射太陽光的方式不同，以及當二氧化碳冰轉變為氣體時發生的大氣壓力變化。
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