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By David McAlary
Washington
11 April 2006
A European spacecraft has arrived at Venus to study Earth's hot, hazy1 sister planet. It is only the latest of many space probes trying to understand why our closest planetary neighbor is an unpleasant greenhouse, rather than a more moderate place supporting life.
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Image provided by European Space Agency ESA shows artist's impression of Venus Express as it enters orbit around Venus
Astronomers2 once thought of Venus as Earth's twin. The two are roughly the same size with about the same mass, density3, and gravity. Now, after more than 20 U.S. and Soviet4 missions to the planet between 1961 and 1994, astronomers consider it Earth's "evil" twin.
The European Space Agency's first mission to the planet, the Venus Express, is to gather data to help explain why.
It has entered orbit after a five-month, 400-million-kilometer journey from the Russian space agency launch site in Kazakhstan. The Venus Express will spend the next month adjusting its extremely oval nine-day path to a circular one lasting5 one day.
"I was a very happy man today, together with my fellow scientists," said the mission's chief scientist, Hakan Svedhem of the Netherlands. "This is really a fantastic experience to see that we end up exactly in the position we wanted to be. Now our work starts. That's very nice work."
Flight operations director Manfred Warhaut, left, poses with a scale model of the European Space Agency Venus Express probe
Svedhem says the European orbiter will pass through Venus' atmosphere for at least 500 days, using state-of-the-art sensors6 to answer questions left by previous explorer craft.
"The noble goal of it all is to understand why is Venus such as it is," he explained. "Why is it not more like Earth? We do know we have life on Earth. We think we do not have any life on Venus. Why is that?"
Venus is broiling7 at 450 degrees Celsius8, shrouded9 by sulfuric acid clouds and a dense10 carbon dioxide atmosphere nearly 100 times thicker than Earth's. A senior editor with Astronomy magazine, Rich Talcott, says this blanket traps heat from the sun, preventing it from escaping.
"There is excellent evidence that Venus was once much more similar to Earth, but what seems to have happened is that it is just a little bit closer to the sun than Earth is and it receives approximately twice as much heat from the sun as Earth," he explained. "That is enough to keep water from existing as liquid on the surface. Over the course of a few billion years, that has been able to drive off all the water on Venus. That means that any of the carbon dioxide that is in the atmosphere cannot get pulled into the oceans as it has on Earth."
By studying Venus, researchers hope to learn lessons that might apply to Earth, where carbon dioxide pollution and other greenhouse gases from industry and automobiles11 collect in our atmosphere.
"That has a lot of importance to scientists," he noted12. "Here on Earth, we are wondering if increases in carbon dioxide will affect the future of Earth's climate. So they are looking at Venus to see if perhaps how conditions that exist there may relate to Earth."
The science gathering13 phase of Europe's Venus Express is to begin June 4, once it reaches its final orbit and it instruments have been checked.
1 hazy | |
adj.有薄雾的,朦胧的;不肯定的,模糊的 | |
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2 astronomers | |
n.天文学者,天文学家( astronomer的名词复数 ) | |
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3 density | |
n.密集,密度,浓度 | |
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4 Soviet | |
adj.苏联的,苏维埃的;n.苏维埃 | |
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5 lasting | |
adj.永久的,永恒的;vbl.持续,维持 | |
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6 sensors | |
n.传感器,灵敏元件( sensor的名词复数 ) | |
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7 broiling | |
adj.酷热的,炽热的,似烧的v.(用火)烤(焙、炙等)( broil的现在分词 );使卷入争吵;使混乱;被烤(或炙) | |
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8 Celsius | |
adj.摄氏温度计的,摄氏的 | |
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9 shrouded | |
v.隐瞒( shroud的过去式和过去分词 );保密 | |
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10 dense | |
a.密集的,稠密的,浓密的;密度大的 | |
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11 automobiles | |
n.汽车( automobile的名词复数 ) | |
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12 noted | |
adj.著名的,知名的 | |
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13 gathering | |
n.集会,聚会,聚集 | |
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