美国宇航局获得土星卫星美马斯清晰图像
文章来源:未知 文章作者:meng 发布时间:2010-03-31 01:11 字体: [ ]  进入论坛
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The highest-resolution-yet temperature map and images of Saturn1(土星) 's icy moon Mimas obtained by NASA's Cassini spacecraft reveal surprising patterns on the surface of the small moon, including unexpected hot regions that resemble "Pac-Man" eating a dot, and striking bands of light and dark in crater2(弹坑,火山口) walls. "Other moons usually grab the spotlight3, but it turns out Mimas is more bizarre(奇异的) than we thought it was," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It has certainly given us some new puzzles."

Cassini collected the data on Feb. 13, during its closest(最靠近的) flyby of the moon, which is marked by an enormous scar called Herschel Crater and resembles the Death Star from "Star Wars."

Scientists working with the composite(合成的,复合的) infrared4 spectrometer(分光仪) , which mapped Mimas' temperatures, expected smoothly5 varying(变化的,不同的) temperatures peaking in the early afternoon near the equator. Instead, the warmest region was in the morning, along one edge of the moon's disk, making a sharply defined Pac-Man shape, with temperatures around 92 Kelvin (minus 294 degrees Fahrenheit). The rest of the moon was much colder, around 77 Kelvin (minus 320 degrees Fahrenheit). A smaller warm spot -- the dot in Pac-Man's mouth -- showed up around Herschel, with a temperature around 84 Kelvin (minus 310 degrees Fahrenheit).

The warm spot around Herschel makes sense because tall crater walls (about 5 kilometers, or 3 miles, high) can trap heat inside the crater. But scientists were completely baffled(阻碍,使迷惑) by the sharp, V-shaped pattern.

"We suspect the temperatures are revealing differences in texture6 on the surface," said John Spencer, a Cassini composite infrared spectrometer team member based at Southwest Research Institute in Boulder7, Colo. "It's maybe something like the difference between old, dense8 snow and freshly fallen powder."

Denser9 ice quickly conducts the heat of the sun away from the surface, keeping it cold during the day. Powdery ice is more insulating(绝缘的,隔热的) and traps the sun's heat at the surface, so the surface warms up.

Even if surface texture variations are to blame, scientists are still trying to figure out why there are such sharp boundaries between the regions, Spencer said. It is possible that the impact that created Herschel Crater melted surface ice and spread water across the moon. That liquid may have flash-frozen into a hard surface.

But it is hard to understand why this dense top layer would remain intact(完整的,原封不动的) when meteorites10(陨星,陨石) and other space debris11(碎片,残骸) should have pulverized12 it by now, Spencer said.

Icy spray from the E ring, one of Saturn's outer rings, should also keep Mimas relatively13 light-colored, but the new visible-light images from the flyby paint a picture of surprising contrasts. Cassini imaging team scientists didn't expect to see dark streaks14(条痕,直横条) trailing down the bright crater walls or a continuous, narrow pile of concentrated dark debris tracing the foot of each wall.

The pattern may appear because of the way the surface of Mimas ages, said Paul Helfenstein, a Cassini imaging team associate based at Cornell University, Ithaca, N.Y. Over time, the moon's surface appears to accumulate a thin veil of silicate15 minerals(硅酸盐矿物) or carbon-rich particles, possibly because of meteor dust falling onto the moon, or impurities16(杂质) already embedded17 in surface ice.

As the sun's warming rays and the vacuum of space evaporate(蒸发,脱水) the brighter ice, the darker material is concentrated and left behind. Gravity pulls the dark material down the crater walls, exposing fresh ice underneath18. Although similar effects are seen on other moons of Saturn, the visibility of these contrasts on a moon continually re-paved with small particles from the E ring helps scientists estimate rates of change on other satellites.

"These processes are not unique to Mimas, but the new high-definition images are like Rosetta stones for interpreting them," Helfenstein said.



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1 Saturn tsZy1     
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 crater WofzH     
n.火山口,弹坑
参考例句:
  • With a telescope you can see the huge crater of Ve-suvius.用望远镜你能看到巨大的维苏威火山口。
  • They came to the lip of a dead crater.他们来到了一个死火山口。
3 spotlight 6hBzmk     
n.公众注意的中心,聚光灯,探照灯,视听,注意,醒目
参考例句:
  • This week the spotlight is on the world of fashion.本周引人瞩目的是时装界。
  • The spotlight followed her round the stage.聚光灯的光圈随着她在舞台上转。
4 infrared dx0yp     
adj./n.红外线(的)
参考例句:
  • Infrared is widely used in industry and medical science.红外线广泛应用于工业和医学科学。
  • Infrared radiation has wavelengths longer than those of visible light.红外辐射的波长比可见光的波长长。
5 smoothly iiUzLG     
adv.平滑地,顺利地,流利地,流畅地
参考例句:
  • The workmen are very cooperative,so the work goes on smoothly.工人们十分合作,所以工作进展顺利。
  • Just change one or two words and the sentence will read smoothly.这句话只要动一两个字就顺了。
6 texture kpmwQ     
n.(织物)质地;(材料)构造;结构;肌理
参考例句:
  • We could feel the smooth texture of silk.我们能感觉出丝绸的光滑质地。
  • Her skin has a fine texture.她的皮肤细腻。
7 boulder BNbzS     
n.巨砾;卵石,圆石
参考例句:
  • We all heaved together and removed the boulder.大家一齐用劲,把大石头搬开了。
  • He stepped clear of the boulder.他从大石头后面走了出来。
8 dense aONzX     
a.密集的,稠密的,浓密的;密度大的
参考例句:
  • The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
  • The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。
9 denser denser     
adj. 不易看透的, 密集的, 浓厚的, 愚钝的
参考例句:
  • The denser population necessitates closer consolidation both for internal and external action. 住得日益稠密的居民,对内和对外都不得不更紧密地团结起来。 来自英汉非文学 - 家庭、私有制和国家的起源
  • As Tito entered the neighbourhood of San Martino, he found the throng rather denser. 蒂托走近圣马丁教堂附近一带时,发现人群相当密集。
10 meteorites 12efd1ed528a28fe1f7cb667a7fbc1e0     
n.陨星( meteorite的名词复数 )
参考例句:
  • Small meteorites have left impact craters all over the planet's surface. 这个行星的表面布满了小块陨石留下的撞击坑。 来自《简明英汉词典》
  • One theory about the existence of extraterrestrial life rests on the presence of carbon compounds in meteorites. 地球外存在生命的理论是基于陨星上存在碳化合物质这一事实的。 来自《简明英汉词典》
11 debris 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。
12 pulverized 12dce9339f95cd06ee656348f39bd743     
adj.[医]雾化的,粉末状的v.将…弄碎( pulverize的过去式和过去分词 );将…弄成粉末或尘埃;摧毁;粉碎
参考例句:
  • We pulverized the opposition. 我们彻底击败了对手。
  • He pulverized the opposition with the force of his oratory. 他能言善辩把对方驳得体无完肤。 来自辞典例句
13 relatively bkqzS3     
adv.比较...地,相对地
参考例句:
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
14 streaks a961fa635c402b4952940a0218464c02     
n.(与周围有所不同的)条纹( streak的名词复数 );(通常指不好的)特征(倾向);(不断经历成功或失败的)一段时期v.快速移动( streak的第三人称单数 );使布满条纹
参考例句:
  • streaks of grey in her hair 她头上的绺绺白发
  • Bacon has streaks of fat and streaks of lean. 咸肉中有几层肥的和几层瘦的。 来自《现代英汉综合大词典》
15 silicate 4EXy2     
n.硅酸盐
参考例句:
  • There are large amounts of aluminum silicate in the area.这个地区有大量的硅酸铝。
  • Silicate minerals are characteristically refractory and difficult to break down.硅酸盐矿物的特点是耐熔和难以分离。
16 impurities 2626a6dbfe6f229f6e1c36f702812675     
不纯( impurity的名词复数 ); 不洁; 淫秽; 杂质
参考例句:
  • A filter will remove most impurities found in water. 过滤器会滤掉水中的大部分杂质。
  • Oil is refined to remove naturally occurring impurities. 油经过提炼去除天然存在的杂质。
17 embedded lt9ztS     
a.扎牢的
参考例句:
  • an operation to remove glass that was embedded in his leg 取出扎入他腿部玻璃的手术
  • He has embedded his name in the minds of millions of people. 他的名字铭刻在数百万人民心中。
18 underneath VKRz2     
adj.在...下面,在...底下;adv.在下面
参考例句:
  • Working underneath the car is always a messy job.在汽车底下工作是件脏活。
  • She wore a coat with a dress underneath.她穿着一件大衣,里面套着一条连衣裙。
TAG标签: moon Nasa map Saturn Mimas
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