文章来源:未知 文章作者:meng 发布时间:2009-12-11 03:02 字体: [ ]  进入论坛

Iapetus伊阿佩托斯 is often called Saturn土星's most bizarre奇异的 moon, due to its starkly明显地 contrasting hemispheres半球 – one black as coal, the other white as snow. Images taken by the Cassini-Huygens spacecraft, orbiting Saturn1 since 2004, offer the most compelling强制性的 evidence to date至今 of why and how the moon got its yin-yang appearance, as well as clues to how other such satellites might have formed in the early universe. Analyzed3 by a research team that includes Cornell scientists, the images are detailed4 in the Dec. 10 online edition of the journal Science.

"This is not the most fundamental problem in the world," said research team member Joseph A. Burns, Cornell's Irving Porter Church Professor of Engineering and professor of astronomy. "But it's an enigma谜 that's been puzzling astronomers6 for centuries."

Since pictures of Iapetus from the Voyager mission 30 years ago confirmed its intriguing迷人的,有趣的 color scheme, scientists have puzzled over whether Iapetus' dark-light contrast was the result of external debris碎片,残骸 hitting some of the moon, or whether the dark dust was the result of internal activity. Now they know the dust came from elsewhere.

Using pictures taken by Cassini, particularly during a September 2007 close fly-by, the scientists assert断言,主张 that Iapetus' darker half, called Cassini Regio, is the result of the planet's leading side getting bombarded被轰击的 by dusty debris8 from another Saturnian moon, Phoebe, which orbits in the opposite direction beyond Iapetus.

It is a longstanding theory, but in a paper published in the journal Nature in October, three Cornell-trained astronomers announced the discovery of an enormous ring of debris ¬– 10,000 times the area of Saturn's famous main ring system – around Saturn, near Phoebe's location, pointing to it as the ring's source. Burns calls this ring the "smoking gun" supporting dust hitting Iapetus and other moons around Saturn.

"The ring of collisional debris that has come off Phoebe and its companion moons is out there, and now we understand the process whereby the stuff is coming in," Burns said. "When you see the coating pattern on Iapetus, you know you've got the right mechanism9 for producing it."

Small, white craters10火山口 that dot Iapetus' darker half indicate a veneer外表,饰面 of dark dust, only meters deep, covering a white, icy surface that matches the rest of the satellite. The imaging data also revealed that all the materials on the leading side are much redder than the shielded and brighter trailing side - another indication that the leading side's dust came from elsewhere.

Other pictures revealed that the transition过渡,转变 from the dark to light hemispheres is not a solid line, but rather a mottled斑驳的,杂色的, patchy不调和的,拼凑成的 array of bright and dark spots.

The pattern, the scientists say, supports a theory described in a companion paper in Science that the darker parts of the moon tend to heat up when struck by sunlight, encouraging the ice to evaporate蒸发,脱水 underneath12.

This causes any dark spots to get even darker, creating the mottled look.


1 Saturn tsZy1     
  • 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 starkly 4e0b2db3ce8605be1f8d536fac698e3f     
adj. 变硬了的,完全的 adv. 完全,实在,简直
  • The city of Befast remains starkly divided between Catholics and Protestants. 贝尔法斯特市完全被处在天主教徒和新教徒的纷争之中。
  • The black rocks stood out starkly against the sky. 那些黑色的岩石在天空衬托下十分显眼。
3 analyzed 483f1acae53789fbee273a644fdcda80     
v.分析( analyze的过去式和过去分词 );分解;解释;对…进行心理分析
  • The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
  • The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程,因为对他来说,爱是个不可分析的迷。 来自《简明英汉词典》
4 detailed xuNzms     
  • He had made a detailed study of the terrain.他对地形作了缜密的研究。
  • A detailed list of our publications is available on request.我们的出版物有一份详细的目录备索。
5 enigma 68HyU     
  • I've known him for many years,but he remains something of an enigma to me.我与他相识多年,他仍然难以捉摸。
  • Even after all the testimonies,the murder remained a enigma.即使听完了所有的证词,这件谋杀案仍然是一个谜。
6 astronomers 569155f16962e086bd7de77deceefcbd     
n.天文学者,天文学家( astronomer的名词复数 )
  • Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
  • 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。 来自《简明英汉词典》
7 intriguing vqyzM1     
  • These discoveries raise intriguing questions. 这些发现带来了非常有趣的问题。
  • It all sounds very intriguing. 这些听起来都很有趣。 来自《简明英汉词典》
8 debris debris     
  • 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。
9 mechanism zCWxr     
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
10 craters 1f8461e3895b38f51c992255a1c86823     
n.火山口( crater的名词复数 );弹坑等
  • 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》
  • The battlefield was full of craters made by exploding shells. 战场上布满弹坑。 来自《现代英汉综合大词典》
11 veneer eLczw     
  • For the first time her veneer of politeness began to crack.她温文尔雅的外表第一次露出破绽。
  • The panel had a veneer of gold and ivory.这木板上面镶饰了一层金和象牙。
12 underneath VKRz2     
  • 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 hemisphere Saturn