Spacecraft Finds Saturn's Rings Dirty and Decaying

 

By David McAlary

The U.S. Cassini spacecraft orbiting Saturn¹ has found evidence that the giant planet's dazzling rings are decaying and may eventually be gone. And the rings are dirtier than thought, too.
Newly revealed Cassini instrument readings taken as the spacecraft approached Saturn from December through March show tons of oxygen dissipating from the outermost² "E" ring, causing its erosion.
University of Southern California scientist Donald Shemansky says oxygen is being knocked out of the ice crystals and other particles that make up the ring, possibly by collisions between them, a meteorite³ impact, or some event like volcano on the nearby moon Enceladus. Without replenishment⁴, Mr. Shemansky says the lifetime of the ring is limited.
"We would project a 100 million year lifetime for the "E" ring, based on the way this process is eroding⁵ away the oxygen out of that system," he said.
Mr. Shemansky suggests that this erosion is occurring in Saturn's other rings too, saying there must be a connection between them.
Scientists estimate the age of the rings at 100 million years and believe they are made of debris⁶ from collisions with the planet's moons or from other bodies that were broken apart when they came near Saturn's powerful gravitational field. The U.S. space agency NASA says Saturn might have had several ring systems over the ages, forming and dissipating many times since the solar system coalesced⁷ out of a disk of dust and gas more than four billion years ago.
Other new evidence from the Cassini spacecraft shows that the icy rings are contaminated with what U.S. Geological Survey researcher Roger Clark says is a dirt-like substance.
"We're calling it dirt for now because we haven't identified specifically what it is because we haven't had enough time to look at the data in detail, but it is a dirt-like signature. So while most of the rings are very, very pure ice, we're now seeing that in some places in the rings, in particular in the gaps and now this "F" ring, we're seeing more dirt than before," he said.
A major goal of the Cassini mission is to study Saturn's biggest moon, Titan. Titan's atmosphere is thought to be like that of Earth millions of years ago before life appeared. The spacecraft has flown by Titan for the first of many close passages over the next four years. It peered through its murky⁸ atmosphere and sent back images showing dark, linear objects on the surface. Project manager Carolyn Porco says this probably means Titan has tectonics, geological processes that on Earth and other solar system bodies gives rise to mountains, volcanoes, and earthquakes.
"Tectonic features would imply internal processes. That will be interesting We're not sure, of course," he said. "If you don't see the surface, you can't read the story of that geology. So this is a glimmer⁹ of what is going on. It may not turn out to be the case, but that's what we think we're seeing now."
In December, the European Huygens spacecraft attached to Cassini will separate to conduct its own probe of Titan by plunging¹⁰ through its atmosphere and landing on the surface.
David McAlary, VOA News, Washington.

注释：
Cassini 卡西尼（太空船）
spacecraft 太空船
Saturn 土星火箭
dazzling 耀眼的
decay 衰减
instrument 装置
oxygen 氧
dissipate 消散
outermost 最外层的
erosion 侵蚀
crystal 晶体
collision 碰撞，冲突
meteorite 陨星
moon 卫星
Enceladus 恩克拉多斯（土星卫星）
estimate 估测
debris 碎片，残骸
gravitational 重力的
NASA（National Aeronautics¹¹ and Space Administration）
(美国)国家航空和宇宙航行局
U.S. Geological Survey 美国地质调查局

1 Saturn   

n.农神，土星

参考例句：

• Astronomers used to ask why only Saturn has rings.天文学家们过去一直感到奇怪，为什么只有土星有光环。
• These comparisons suggested that Saturn is made of lighter materials.这些比较告诉我们，土星由较轻的物质构成。

2 outermost   

adj.最外面的，远离中心的

参考例句：

• He fired and hit the outermost ring of the target.他开枪射中了靶子的最外一环。
• The outermost electron is shielded from the nucleus.原子核对最外层电子的作用受到屏蔽。

3 meteorite   

n.陨石；流星

参考例句：

• The meteorite in Jilin Exhibition Hall is believed to be the largest in the world.吉林展览馆的陨石被认为是世界上最大的。
• The famous Murchison meteorite smashed into the Australian ground in 1969.1969年著名的默奇森陨石轰然坠落在澳大利亚。

4 replenishment   

n.补充(货物)

参考例句：

• Since the wartime population needed replenishment, pregnancies were a good sign. 最后一桩倒不失为好现象，战时人口正该补充。
• Natural replenishment of this vast supply of underground water occurs very slowly. 靠自然补充大量地下水是十分缓慢的。

5 eroding   

侵蚀，腐蚀( erode的现在分词 )； 逐渐毁坏，削弱，损害

参考例句：

• The coast is slowly eroding. 海岸正慢慢地被侵蚀。
• Another new development is eroding the age-old stereotype of the male warrior. 另一个新现象是，久已形成的男人皆武士的形象正逐渐消失。

6 debris   

n.瓦砾堆，废墟，碎片

参考例句：

• After the bombing there was a lot of debris everywhere.轰炸之后到处瓦砾成堆。
• Bacteria sticks to food debris in the teeth,causing decay.细菌附着在牙缝中的食物残渣上，导致蛀牙。

7 coalesced   

v.联合，合并( coalesce的过去式和过去分词 )

参考例句：

• The puddles had coalesced into a small stream. 地面上水洼子里的水汇流成了一条小溪。
• The views of party leaders coalesced to form a coherent policy. 党的领导人的各种观点已统一为一致的政策。 来自辞典例句

8 murky   

adj.黑暗的，朦胧的；adv.阴暗地，混浊地；n.阴暗；昏暗

参考例句：

• She threw it into the river's murky depths.她把它扔进了混浊的河水深处。
• She had a decidedly murky past.她的历史背景令人捉摸不透。

9 glimmer   

v.发出闪烁的微光；n.微光，微弱的闪光

参考例句：

• I looked at her and felt a glimmer of hope.我注视她，感到了一线希望。
• A glimmer of amusement showed in her eyes.她的眼中露出一丝笑意。

10 plunging   

adj.跳进的，突进的v.颠簸( plunge的现在分词 )；暴跌；骤降；突降

参考例句：

• War broke out again, plunging the people into misery and suffering. 战祸复发，生灵涂炭。 来自《现代汉英综合大词典》
• He is plunging into an abyss of despair. 他陷入了绝望的深渊。 来自《简明英汉词典》

11 aeronautics   

n.航空术，航空学

参考例句：

• National Aeronautics and Space undertakings have made great progress.国家的航空航天事业有了很大的发展。
• He devoted every spare moment to aeronautics.他把他所有多余的时间用在航空学上。