文章来源:未知 文章作者:meng 发布时间:2010-06-25 07:17 字体: [ ]  进入论坛

ESA's Venus Express is helping1 planetary(行星的) scientists investigate whether Venus once had oceans. If it did, it may even have begun its existence as a habitable planet similar to Earth. These days, Earth and Venus seem completely different. Earth is a lush(苍翠繁茂的) , clement2(温和的,仁慈的) world teeming3 with(富于,充满) life, whilst Venus is hellish(地狱的,凶恶的) , its surface roasting at temperatures higher than those of a kitchen oven.

But underneath4 it all the two planets share a number of striking similarities. They are nearly identical in size and now, thanks to ESA's Venus Express orbiter, planetary scientists are seeing other similarities too.

"The basic composition of Venus and Earth is very similar," says Håkan Svedhem, ESA Venus Express Project Scientist. Just how similar planetary scientists from around the world will be discussing in Aussois, France, where they are gathering5 this week for a conference.

One difference stands out: Venus has very little water. Were the contents of Earth's oceans to be spread evenly across the world, they would create a layer 3 km deep. If you were to condense(浓缩,凝结) the amount of water vapour(水蒸汽) in Venus' atmosphere onto its surface, it would create a global puddle6(水坑,泥潭) just 3 cm deep.

Yet there is another similarity here. Billions of years ago, Venus probably had much more water. Venus Express has certainly confirmed that the planet has lost a large quantity of water into space.

It happens because ultraviolet radiation from the Sun streams into Venus' atmosphere and breaks up the water molecules7 into atoms: two hydrogens and one oxygen. These then escape to space.

Venus Express has measured the rate of this escape and confirmed that roughly twice as much hydrogen is escaping as oxygen. It is therefore believed that water is the source of these escaping ions. It has also shown that a heavy form of hydrogen, called deuterium(重氢) , is progressively enriched in the upper echelons8(阶层) of Venus's atmosphere, because the heavier hydrogen will find it less easy to escape the planet's grip.

"Everything points to there being large amounts of water on Venus in the past," says Colin Wilson, Oxford9 University, UK. But that does not necessarily mean there were oceans on the planet's surface.

Eric Chassefière, Université Paris-Sud, France, has developed a computer model that suggests the water was largely atmospheric10 and existed only during the very earliest times, when the surface of the planet was completely molten. As the water molecules were broken into atoms by sunlight and escaped into space, the subsequent drop in temperature probably triggered the solidification11(凝固,浓缩) of the surface. In other words: no oceans.

Although it is difficult to test this hypothesis it is a key question. If Venus ever did possess surface water, the planet may possibly have had an early habitable phase.

Even if true, Chassefière's model does not preclude12(排除,妨碍) the chance that colliding comets brought additional water to Venus after the surface crystallised, and these created bodies of standing13 water in which life may have been able to form.

There are many open questions. "Much more extensive modelling of the magma(岩浆) ocean–atmosphere system and of its evolution is required to better understand the evolution of the young Venus," says Chassefière.

When creating those computer models, the data provided by Venus Express will prove crucial(重要的,决定性的) .


1 helping 2rGzDc     
  • The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
  • By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。
2 clement AVhyV     
  • A clement judge reduced his sentence.一位仁慈的法官为他减了刑。
  • The planet's history contains many less stable and clement eras than the holocene.地球的历史包含着许多不如全新世稳定与温和的地质时期。
3 teeming 855ef2b5bd20950d32245ec965891e4a     
adj.丰富的v.充满( teem的现在分词 );到处都是;(指水、雨等)暴降;倾注
  • The rain was teeming down. 大雨倾盆而下。
  • the teeming streets of the city 熙熙攘攘的城市街道
4 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。
5 gathering ChmxZ     
  • He called on Mr. White to speak at the gathering.他请怀特先生在集会上讲话。
  • He is on the wing gathering material for his novels.他正忙于为他的小说收集资料。
6 puddle otNy9     
  • The boy hopped the mud puddle and ran down the walk.这个男孩跳过泥坑,沿着人行道跑了。
  • She tripped over and landed in a puddle.她绊了一下,跌在水坑里。
7 molecules 187c25e49d45ad10b2f266c1fa7a8d49     
分子( molecule的名词复数 )
  • The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
  • Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里,大分子裂变为小分子。
8 echelons 8c417a0cc95d6d9e9c600428a3144f86     
n.(机构中的)等级,阶层( echelon的名词复数 );(军舰、士兵、飞机等的)梯形编队
  • Officers were drawn largely from the top echelons of society. 这些官员大都来自社会上层。 来自《简明英汉词典》
  • Except in the higher echelons, extensive classification has no place in the classification of vegetation. 除高阶类级之外,外延分类在植物分类中还是没有地位的。 来自辞典例句
9 Oxford Wmmz0a     
  • At present he has become a Professor of Chemistry at Oxford.他现在已是牛津大学的化学教授了。
  • This is where the road to Oxford joins the road to London.这是去牛津的路与去伦敦的路的汇合处。
10 atmospheric 6eayR     
  • Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
  • Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。
11 solidification 2435a3c11e5a5ed897dcac42fc6c8afd     
  • In the process of solidification the same amount of heat is released. 在固结过程中则将释放出同等的热量。
  • The solidification mechanism and adhering formation of the product are also discussed. 对锌粉的凝固机理及粘结现象进行了探讨。
12 preclude cBDy6     
  • We try to preclude any possibility of misunderstanding.我们努力排除任何误解的可能性。
  • My present finances preclude the possibility of buying a car.按我目前的财务状况我是不可能买车的。
13 standing 2hCzgo     
  • After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
  • They're standing out against any change in the law.他们坚决反对对法律做任何修改。
TAG标签: water earth Venus