2. 外语
  3. Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters

Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters

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问题     Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters because each is similar in mass to Jupiter, the largest solar-system planet, but orbits its parent star at a fraction of the distance at which Earth, let alone Jupiter, orbits the Sun. In the standard, solar-system-based theory of planetary formation, such as a massive planet could not form so close to a star. So most attempts to explain a hot Jupiter’s existence envision it forming farther away, then migrating inward. According to one hypothesis, the planet’s gravitational field tugs on the protoplanetary disk of dust and gas from which it formed. The disk exerts its own gravitational tug, and this interplay of forces robs the planet of momentum in its orbital path, forcing it to spiral in toward the star. According to another hypothesis, the planet’s gravitational field is so strong that it creates a groove in the disk, partitioning it into inner and outer regions; the resulting gravitational interactions between the planet and these regions cause the planet to lose orbital momentum and spiral inward. Another question remains: what prevents the planet from continuing its spiral until it collides with the star?
The author of the passage mentions “Earth” primarily in order to
选项 A、stress the massive size of a hot Jupiter
B、emphasize the proximity of a hot Jupiter to its parent star
C、imply that hot Jupiters are unlikely to harbor extraterrestrial life
D、point out differences between Earth and Jupiter with regard to their orbital distance from the Sun
E、illustrate how hot Jupiters might fit into the standard theory of planetary formation
答案B
解析 “地球”所在句子的3s版本是为了提出一个问题：为什么热木星距离恒星那么近，因此选项B正确。D项要注意“木星”和“热木星”是不一样的概念。
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