英语听力：自然百科 探索世界奥秘之Alien Neighbors (寻访外星人) Unit10（在线收听）

…cold conditions that earth has to offer. Professor Freeman believes these rugged microorganisms are probably capable of surviving on Mars. Mars is certainly our best bet for finding life in the inner solar system. But the chances of life existing in the outer solar system have never been more promising than at present. Jupiter, Saturn, Uranus and Neptune are the gas planets of the outer solar system.

In Massachusetts at MIT, Heidi Hammel has investigated the unforgiving environments of the gas giants. She is not optimistic about finding life on the planets themselves.

"Even though those planets do get somewhat warm deep inside them, at the pressures and temperatures of the outermost clouds, they are just too cold ,they are too cold and it's too dark .There is just not enough sunlight there , there is no liquid water, and that's what we need to sustain life. So it's not likely."

Artists and science fiction writers may image that there are weird jellyfish floating around Jupiter, but it's most unlikely.

Freezing Pluto on the other hand is a world of rock and ice, not a ball of gas like the 4 giant planets. The outermost planet Pluto is certainly too cold and dark to be a serious candidate for finding life. There are nearly 60 moons in the outer solar system. Research so far shows that most of them are inhospitable to life as we know it, but there are 2 exceptions. One is Titan, Saturn's largest moon. In November 2004, the Hoygan's probe will parachute though the clouds of Titan. It could splash down in a bitterly cold ocean or a lake of liquid hydrocarbons or even on a solid surface. Titan is like a frozen early earth.It has many substances that were around on earth before life began. The Hoygans probe will explore whether Titan has the potential to spring to life.

"Well, the organic chemistry in the atmosphere of Titan is particularly interesting and may provide us some real interesting insights into the nature of prebiotic chemistry. It may have also produced life ,we just don't know.In the future, Titan could look like this. When our sun expands to 50 times its present size,5 billion years from now, Titan will receive as much energy as earth does today. For a short time it might well become a blue ocean world, where life thrives. In the meantime, Jupiter's rocky moon Europa is the most exciting candidate for finding life in the outer solar system. In 1996 the Galileo Space Craft returned the most exciting evidence yet, that Europa has oceans, oceans that could teem with life. Galileo's images revealed areas where ice fragments have broken and moved apart like pieces of a jigsaw puzzle. The cracks suggest that the ice is shifting on a dynamic surface.

words in this passage

best bet:Your best bet is the action which is most likely to be successful.最好的办法

例句：If you want to get to the station before 10 o'clock, your best bet would be to take a taxi.

Uranus：the planet seventh in order of distance from the Sun, after Saturn and before Neptune天王星

hydrocarbon：a chemical combination of hydrogen and carbon, such as in oil or petrol烃, 碳氢化合物

jigsaw puzzle：a picture stuck onto wood or cardboard and cut into irregular pieces which must be joined together correctly to form the picture again七巧板, 智力拼图玩具