2007年VOA标准英语-US Spacecraft Gathers Hints of Underground Wate

By David McAlary
Washington
15 February 2007

A U.S. spacecraft has provided fresh evidence that water once flowed on Mars. In this case, it is water that ran deep underground through rock fissures¹, places where scientists say life could have thrived hidden from the harsh Martian surface environment. VOA's David McAlary reports.

 
Satellite photo showing erosion of rock formations on Mars
The U.S. space agency NASA's newest satellite around the red planet, the Mars Reconnaissance Orbiter, has taken color pictures showing a landscape called Chasma Canyon² composed of dozens of alternating layers of dark and light toned rocks and crossed by dark sand dunes³.

Within those layers, the detailed⁴ images show fractures, called joints⁵, surrounded by light colored bedrock that was once deep underground before erosion exposed it. University of Arizona researcher Chris Okubo argues that this brighter bedrock is clear evidence that a liquid flowed through it and washed the dark minerals away, as water has done in similar situations on Earth.

"So the unaltered rock has this dark brown color. However, along the joints you see that the dark brown minerals have been chemically removed by the fluids that were flowing within the joints, so the area has been bleached," he said.

 
Chris Okubo

In a paper in the journal Science, Okubo and a colleague say the bleaching⁶ would have taken a long time to occur - perhaps hundreds of millions or a few billion years. He explained at a scientific meeting in San Francisco that an underground setting for water could have been conducive⁷ for life on Mars.

"The fact that these areas were underground is important because the overlying several kilometers of rock would have acted as buffers⁸ against any sort of harsh environmental conditions that may have existed at the surface of Mars at this time. So these areas would be nice protected areas for any sort of biologic processes to occur," he said.

Previous findings by NASA robot rovers on Mars have shown that water once flowed on the surface and may have formed lakes and even oceans. Recent photos of fresh gullies from another U.S. satellite indicate it might still be percolating⁹ up from underground.

Mars water specialist Stephen Clifford of the Lunar and Planetary Institute in Houston, Texas, says Okubo's research supports the notion that ground water remains¹⁰ beneath the Martian surface crust.

"The fact that there is such persuasive¹¹ evidence of joints and fractures in the crust also suggests that this groundwater had an ability to flow enormous distances. That has implications for understanding the processes that led to the redistribution of water from surface environments like lakes and seas into the subsurface, into that increasingly thick layer of frozen ground that was the result of both the external climate cooling and the decline of the planet's internal heat flow," he said.

Okubo says his analysis awaits confirmation¹² by a future generation of Mars rovers, which could check the chemical composition of the rocks up close.

1 fissures   

n.狭长裂缝或裂隙( fissure的名词复数 )；裂伤；分歧；分裂v.裂开( fissure的第三人称单数 )

参考例句：

• Rising molten rock flows out on the ocean floor and caps the fissures, trapping the water. 上升熔岩流到海底并堵住了裂隙，结果把海水封在里面。 来自辞典例句
• The French have held two colloquia and an international symposium on rock fissures. 法国已经开了两次岩石裂缝方面的报告会和一个国际会议。 来自辞典例句

2 canyon   

n.峡谷，溪谷

参考例句：

• The Grand Canyon in the USA is 1900 metres deep.美国的大峡谷1900米深。
• The canyon is famous for producing echoes.这个峡谷以回声而闻名。

3 dunes   

沙丘( dune的名词复数 )

参考例句：

• The boy galloped over the dunes barefoot. 那男孩光着脚在沙丘间飞跑。
• Dragging the fully laden boat across the sand dunes was no mean feat. 将满载货物的船拖过沙丘是一件了不起的事。

4 detailed   

adj.详细的，详尽的，极注意细节的，完全的

参考例句：

• 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 joints   

接头( joint的名词复数 )； 关节； 公共场所（尤指价格低廉的饮食和娱乐场所） （非正式）； 一块烤肉 （英式英语）

参考例句：

• Expansion joints of various kinds are fitted on gas mains. 各种各样的伸缩接头被安装在煤气的总管道上了。
• Expansion joints of various kinds are fitted on steam pipes. 各种各样的伸缩接头被安装在蒸气管道上了。

6 bleaching   

漂白法，漂白

参考例句：

• Moderately weathered rock showed more intense bleaching and fissuring in the feldspars. 中等风化岩石则是指长石有更为强烈的变白现象和裂纹现象。
• Bleaching effects are very strong and show on air photos. 退色效应非常强烈，并且反映在航空象片上。

7 conducive   

adj.有益的，有助的

参考例句：

• This is a more conducive atmosphere for studying.这样的氛围更有利于学习。
• Exercise is conducive to good health.体育锻炼有助于增强体质。

8 buffers   

起缓冲作用的人（或物）( buffer的名词复数 )； 缓冲器； 减震器； 愚蠢老头

参考例句：

• To allocate and schedule the use of buffers. 分配和计划缓冲器的使用。
• Number of times the stream has paused due to insufficient stream buffers. 由于流缓冲区不足导致流程暂停的次数。

9 percolating   

n.渗透v.滤( percolate的现在分词 )；渗透；（思想等）渗透；渗入

参考例句：

• Bubbles simply supply a short cut for the faster-moving percolating gas. 气泡不过是对快速运动的渗透气体提供了一条捷径。 来自辞典例句
• I' ll percolate some coffee, ie make it by percolating. 我去用过滤法煮些咖啡。 来自辞典例句

10 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

11 persuasive   

adj.有说服力的，能说得使人相信的

参考例句：

• His arguments in favour of a new school are very persuasive.他赞成办一座新学校的理由很有说服力。
• The evidence was not really persuasive enough.证据并不是太有说服力。

12 confirmation   

n.证实，确认，批准

参考例句：

• We are waiting for confirmation of the news.我们正在等待证实那个消息。
• We need confirmation in writing before we can send your order out.给你们发送订购的货物之前，我们需要书面确认。