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  3. Mars with its orange-red colour has fascinated people since ancient times. Its name derives from the Roman god of war. The plane

Mars with its orange-red colour has fascinated people since ancient times. Its name derives from the Roman god of war. The plane

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问题     Mars with its orange-red colour has fascinated people since ancient times. Its name derives from the Roman god of war. The planet is similar to Earth in a number of ways. For example, a day on Mars is about the same length as a day on Earth. Also the tilt of Mars’ axis is about the same as that of Earth so it has similar seasons.
    However, temperatures are much lower than on Earth—below the freezing temperature of water even in summer with average daily temperatures of about 60 degrees Celsius. The cold is due to the lack of heating from the Sun and the lack of greenhouse warming from gases in the thin atmosphere.
    What can you see?
    Mars will be a very prominent object in the night sky in August and September. Not only will it be the brightest object apart from the moon, but its reddish colour will make it easy to find.
    In July Mars was rising in the east a few hours after sunset. By late August it will be rising around sunset.

    To see Mars through a telescope during its close approach, contact your local public observatory, amateur astronomical society or planetarium. Most of them are likely to hold viewing sessions.
    Mars is a small planet, half the size of Earth. When it is distant from us it appears as a tiny featureless reddish disc even when viewed through a telescope. At oppositions the disc of Mars appears larger and features can be seen on its surface.
    These features include the polar caps and dark markings. Mars may also have a dust storm raging on its surface. While this sounds exciting, it can make the appearance of the planet disappointing.
    Water on Mars
    Though there is no liquid water on the surface, close-up photographs of Mars reveal winding valleys and channels. These indicate the existence of running water in the past.
    Scientists using NASA’s Mars Odyssey spacecraft, currently in orbit around Mars, have discovered large quantities of water ice under the planet’s surface. They found that in regions of Mars surrounding the south pole the top one meter of soil has more than 50% water by volume. An instrument called the gamma ray spectrometer detected the water by searching for the signature of hydrogen in radiation coming from the planet. As hydrogen is an essential component of water and the hydrogen-rich regions are in the coldest regions of the planet, the scientists concluded that the hydrogen indicated the presence of water ice.
    Summary:
    The Mars and the Earth have much in common, such as similar length of a day and similar【51】However, the temperature is【52】on Mars than that on Earth. In August and September, Mars is the brightest object in the night sky secondary to【53】. ff you want to observe the Mars, you can contact your local public observatory, amateur astronomical society or planetarium, who are likely to provide viewing sessions. At oppositions the Mars appears larger and【54】can be seen on its surface. Evidence show that there is no liquid water on the Mars but【55】was detected, which is an essential element of water.  
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答案hydrogen
解析 (文章最后一段提到An instrument called the gamma ray spectrometer detected the water by searching for the signature of hydrogen in radiation coming from the planet. r射线探测器探测到了星球上有氢。但火星上并没有水，科学家认为氢的存在表明water ice的存在。)  
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大学生英语竞赛（NECCS）

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