2007年VOA标准英语-US Spacecraft Finds Signs of Seas on Saturn's B

By David McAlary
Washington
14 March 2007

A U.S. spacecraft studying Saturn¹ has found evidence of large seas on its biggest moon, Titan. But if they are seas, they would not be filled with water. Instead, as VOA's David McAlary reports, they would be liquid beds of the hydrocarbon² methane³, normally a flammable gas on the much warmer Earth.

A comparison view of a lake on Titan and Lake Superior

The Cassini spacecraft, which arrived to orbit Jupiter in 2004, has spotted⁴ several dark, sea-like features near Titan's north pole.

In January, the orbiter's radar⁵ had viewed features the size of lakes on Saturn's moon, but Cassini scientist Stephen Wall of the Jet Propulsion Laboratory in California says the shapes just discovered are much larger.

"We have seen bodies of liquid that are big enough to be seas," he said. "One of them in particular is the size of a small sea on the Earth."

Titan is the solar system's second largest moon, 50 percent larger than Earth's moon. The body Wall mentions stretches nearly 1,100 kilometers to about half way down Titan's northern hemisphere. This makes it only slightly smaller than the Caspian Sea.

There is no definite proof that this and the other apparent seas contain liquid, and additional fly-overs will be necessary for confirmation⁶. But Wall says their dark appearance in radar indicates smoothness, and other properties point to the presence of liquids.

"We have now seen all of those things that you would typically associate with a body of water on the Earth - inlets and bays and channels and evidence of flow, drainage basins - all of those things," he said. "We know that it cannot be water on Titan because it is too cold, so we suspect that it is methane, which is right at the point where it can condense and evaporate."

Because methane is a major part of Titan's mostly nitrogen atmosphere, scientists have long believed that the moon has oceans filled with it . Titan is the only other body in the solar system known to have an active liquid cycle where the liquid evaporates from the surface and eventually recondenses as rainfall.

But the dense⁷ methane haze⁸ has hidden the view. Radar penetrates⁹ the haze and the earlier findings of probable lakes strengthened the belief in methane oceans. The new radar images add to the evidence.

As a result, Cassini team members will be re-pointing the spacecraft's radar during a fly-over in May so it can pass directly over the dark areas seen from farther away.

1 Saturn   

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 hydrocarbon   

n.烃，碳氢化合物

参考例句：

• During incomplete combustion some of the hydrocarbon fuel is cracked.在不完全的燃烧中，一些烃燃料裂解。
• The hydrocarbon must be an alkene.这个碳氢化合物必定是烯烃。

3 methane   

n.甲烷，沼气

参考例句：

• The blast was caused by pockets of methane gas that ignited.爆炸是由数袋甲烷气体着火引起的。
• Methane may have extraterrestrial significance.甲烷具有星际意义。

4 spotted   

adj.有斑点的，斑纹的，弄污了的

参考例句：

• The milkman selected the spotted cows,from among a herd of two hundred.牛奶商从一群200头牛中选出有斑点的牛。
• Sam's shop stocks short spotted socks.山姆的商店屯积了有斑点的短袜。

5 radar   

n.雷达，无线电探测器

参考例句：

• They are following the flight of an aircraft by radar.他们正在用雷达追踪一架飞机的飞行。
• Enemy ships were detected on the radar.敌舰的影像已显现在雷达上。

6 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。

7 dense   

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。

8 haze   

n.霾，烟雾；懵懂，迷糊；vi.(over)变模糊

参考例句：

• I couldn't see her through the haze of smoke.在烟雾弥漫中，我看不见她。
• He often lives in a haze of whisky.他常常是在威士忌的懵懂醉意中度过的。

9 penetrates   

v.穿过( penetrate的第三人称单数 )；刺入；了解；渗透

参考例句：

• This is a telescope that penetrates to the remote parts of the universe. 这是一架能看到宇宙中遥远地方的望远镜。 来自《简明英汉词典》
• The dust is so fine that it easily penetrates all the buildings. 尘土极细，能极轻易地钻入一切建筑物。 来自辞典例句