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  3. In its first month orbiting Saturn, the Cassini spacecraft has detected a new radiation belt in an unexpected place, its invisib

In its first month orbiting Saturn, the Cassini spacecraft has detected a new radiation belt in an unexpected place, its invisib

admin2014-01-07  11
问题     In its first month orbiting Saturn, the Cassini spacecraft has detected a new radiation belt in an unexpected place, its invisible swarm of trapped high-energy particles circling the planet inside the inner edge of Saturn’s signature disk of luminous rings.
    Scientists who reported the discovery said yesterday that they were surprised to find a relatively small radiation belt completely isolated from a planet’s main radiation belts, which lie at much greater distances. They had not expected that such a concentration of energetic particles could be sustained inside the famous Saturnian rings.
    The phenomenon of a single isolated belt, the scientists said, has never been observed at any other planet in the solar system. By contrast, the Van Allen belts of Earth consist of two related regions of intense radiation trapped by the planet’s magnetic field.
    In a NASA conference call with reporters, Dr. Donald G. Mitchell, a Cassini mission scientist from Johns Hopkins University, said the newly discovered radiation belt was detected as the spacecraft made its closest approach to Saturn immediately after rocketing into its orbit on July 1. No previous spacecraft visiting Saturn had been in the proper position to make such a discovery.
    Dr. Mitchell said it was the spacecraft’s imaging magnetometer that had observed the radiation belt, which extended around Saturn from about 15,000 miles above the planet’s cloud tops to the inner edge of the innermost of its spectacular rings. The belt is much smaller, and the energies of its particles are less intense, than Saturn’s main radiation belts.
    With its discovery, Dr. Mitchell said, "we have seen something that we did not expect: that radiation belt particles can hop over obstructions like Saturn’s rings."
    Other Cassini mission scientists reported puzzling patterns of lightning and thunderstorms on Saturn and observations of a striking glow emanating day and night from the planet’s largest moon, Titan.
It can be inferred from the passage that
选项 A、The newly-discovered belt is in fact the outmost layer of Saturn.
B、We can’t see the newly-discovered belt without the help of imaging magnetometer.
C、There can hardly be any belts similar as the newly discovered one at any other planet in the solar system
D、The main radiation belts aren’t connected with Saturnian rings at all.
答案D
解析 第5段和第6段谈到，该新发现的辐射带在土星大气层顶端外1．5万英里开始，延伸到其最里层的土星环的内缘。在该辐射带与土星环的交接处，当有辐射颗粒hop over obstructions like Saturn’s rings．这一点是科学家们未曾估计到的东西。由此可见，先前所有的辐射带中，都没有发生过辐射颗粒跨越土星环之事，也就是说，其他各主要辐射带均与土星环相距甚远。所以D正确。
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