A radar map of the Martian north pole reveals a four-layer ice structure laid down over a period of five million years. The ice structure is on top of sedimentary rocks hundreds of kilometers thick, scientists said earlier this month in a report.
The data was provided by NASA’s Mars Reconnaissance Orbiter. It provides ground-breaking insight into the formation of the Martian ice cap and the “thermal history” of the red planet, said Roger Phillips of Southwest Research Institute in Boulder, Colorado, US.
PHOTO: AP
Researchers found that the polar cap is formed by up to four layers of ice rich in sand and dust, separated by clearer sheets of ice. They believe the structure of the polar cap is the result of variations in Mars’ orbit over the years. One Martian year equals 1.88 Earth years.
The ice layers were accumulated over a period of about five million Earth years, said the scientists in a paper published in Science.
The radar images also show that the underlying sedimentary rocks have not been deformed by the enormous weight of the ice cap, suggesting that the Martian crust in the area is more than 300km thick.
The radar mapping of the polar cap also allows scientists to track the movement of dust over the Martian landscape over the years, researchers said.
The Martian north pole is part of a vast sedimentary plain built up over more than three billion years from ice erosion deposits, dust, volcanic lava and other sundry materials.
(AFP)
本月稍早科學家在一份報告中表示，從火星北極傳回來的雷達影像顯示，該地有超過五百萬年之久的四層凍土層，而凍土層的下方是厚達數百公里的沉積岩層。
美國科羅拉多州波德市西南研究所的羅傑．飛利浦斯說，美國航太總署的火星偵察軌道器回傳的這些前所未見的照片，讓人類可以一窺這顆紅色星球的「熱歷史」，及其冰帽結構。
研究學家發現，北極極冠是由四層富含沙塵的冰層組成，層間則被更清純的冰層分隔。科學家認為，北極極冠會出現這樣的結構，是火星經年軌道變遷的結果。火星上的一年，約等於地球上的一點八八年。
科學家在發表於《科學》雜誌的文章中指出，這些凍土層是經過約五百萬年（地球年）沉積而成。
這些雷達影像也顯示，下層的沉積岩並沒有被極重的冰帽壓到變形，這意味著火星該區地殼的厚度超過三百公里。
研究人員表示，科學家也能透過火星極冠的雷達影像，來追蹤這幾年火星地貌改變的情形。
三十多億年來，冰蝕沉積物、 塵土、火山熔岩和其他各式各樣的物質，在火星上沉積成一片遼闊的平原，而火星北極就是其中一部分。
（法新社�翻譯：袁星塵）
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