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“Possibility of life”— scientists map Saturn’s exotic moon Titan
科學家公布「泰坦星」地圖 探索生命存在可能性

NASA’s planned Dragonfly rotorcraft lander approaches a site to explore on Saturn’s moon, Titan, in an Illustration released on June 27.
這張發布於六月二十七日的模擬圖,展示美國太空總署計畫發射的「蜻蜓號」旋翼機登陸器,正在接近土星衛星「泰坦」表面一處地點,準備進行探勘。

Photo: Reuters
照片:路透

Scientists on Monday unveiled the first global geological map of Saturn’s moon Titan including vast plains and dunes of frozen organic material and lakes of liquid methane, illuminating an exotic world considered a strong candidate in the search for life beyond Earth.

The map was based on radar, infrared and other data collected by NASA’s Cassini spacecraft, which studied Saturn and its moons from 2004 to 2017. Titan, with a diameter of 5,150km, is the solar system’s second-biggest moon behind Jupiter’s Ganymede. It is larger than the planet Mercury.

Organic materials — carbon-based compounds critical for fostering living organisms — play a leading role on Titan. “Organics are very important for the possibility of life on Titan, which many of us think likely would have evolved in the liquid water ocean under Titan’s icy crust,” said planetary geologist Rosaly Lopes of NASA’s Jet Propulsion Laboratory in California. “Organic materials can, we think, penetrate down to the liquid water ocean and this can provide nutrients necessary for life, if it evolved there,” added Lopes, who led the research published in the journal Nature Astronomy.

On Earth, water rains down from clouds and fills rivers, lakes and oceans. On Titan, clouds spew hydrocarbons like methane and ethane — which are gases on Earth — in liquid form due to the moon’s frigid climate. Rainfall occurs everywhere on Titan, but the equatorial regions are drier than the poles, said study co-author Anezina Solomonidou, a European Space Agency research fellow.

Plains (covering 65 percent of the surface) and dunes (covering 17 percent of the surface) made up of frozen bits of methane and other hydrocarbons dominate Titan’s mid-latitudes and equatorial regions, respectively.

Titan is the only solar system object other than Earth boasting stable liquids on the surface, with lakes and seas full of methane being major features at its polar regions. Hilly and mountainous areas, thought to represent exposed portions of Titan’s crust of water ice, represent 14 percent of the surface.

“What is really fun to think about is if there are any ways that those more complex organics can go down and mix with water in the deep icy crust or deep subsurface ocean,” JPL scientist and study co-author Michael Malaska said. Noting that on Earth there is a bacterium that can survive just on a hydrocarbon called acetylene and water, Malaska asked, “Could it or something like it live in Titan deep in the crust or ocean where temperatures are a little warmer?”

The map was created seven years before the US space agency is set to launch its Dragonfly mission to dispatch a multi-rotor drone to study Titan’s chemistry and suitability for life. Dragonfly is scheduled to reach Titan in 2034. “It is not only scientifically important but also really cool — a drone flying around on Titan,” Lopes said. “It will be really exciting.”

(Reuters)

科學家在週一公布史上第一張土星衛星「泰坦」的全球地質圖,其中包含許多廣闊的平原,冰凍有機物質構成的沙丘,以及液態甲烷形成的湖泊,揭露這片咸認為是地球以外生命搜尋重要候選地點的奇特世界。

該地質圖是根據美國國家航空暨太空總署的卡西尼太空探測船,在二○○四年到二○一七年間研究土星及其衛星時,收集到的雷達、紅外線等資料。直徑達五千一百五十公里的泰坦星,是我們太陽系第二大的衛星,僅次於木星的衛星蓋尼米德。泰坦甚至比水星還大。

有機物質──也就是對於培養生物體而言非常關鍵的碳基化合物──在泰坦星上扮演重要角色。美國太空總署加州噴射推進實驗室的行星地質學家羅莎莉‧洛佩茲指出:「有機物對於泰坦形成生命的可能性至關重要,我們有許多人認為,生命可能在泰坦結冰地殼底下的液態海洋中進行演化。」這篇研究發表於《自然‧天文》期刊,主持該研究的洛佩茲補充說:「我們認為,有機物質會向下滲透到液態海洋,如果其中有生命演化,就能為生命提供必要營養物。」

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