GMAT真题阅读—重力异常

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When a large body strikes a planet or moon,material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of the material that has been ejected to make the hole results in an area of slightly lower gravity than surrounding would therefore expect that all of the large multi- ring impact basins on the surface of Earth's Moon would show such negative gravity anomalies, since they are, essentially, large holes in the lunar surface. Yet data collected in 1994 by the Clementine spacecraft show that many of these lunar basins have no anomalously low gravity and some even have anomalously high gravity. Scientists speculate that early in lunar history, when large impactors struck the Moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the Moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no low gravity anomaly in the resulting basin. Later, however, as the Moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of the Moon is too cold and stiff.

当一个大型物体撞击一颗行星或者卫星时，会出现物质喷射，所以行星上会出现坑和质量的亏损。这种亏损表现为重力的异常：被喷射出去从而形成坑的物质的移除导致了一个区域的重力略低于其周边区域。所以有人会预期所有月球表面的`多重环形冲击盆地都会显示负的重力异常，因为从本质上来说，他们都是月球表面的大坑。但是1994年由Clementine宇宙飞船手机的数据显示许多这种月球盆地没有异常的低重力并且一些甚至有异常的高重力。科学家们推测在月球历史的早期，当大型冲击体撞击月球表面时，导致了成千上万立方千米的地壳物质喷射，来自月球月幔的高密度物质迅速上涌覆盖了冲击体，补偿了喷射出去的物质，所以在形成的盆地中没有留下异常的低重力。然而在此之后，随着月球变得越来越冷，越来越没有弹性，来自大型冲击体的回弹变得部分而不完整。所以在今天，这样的重力不常将不会再出现：因为月球的表面太过寒冷和坚硬。01Question 1

According to the passage, the gravitational compensation in the highlighted text is caused by of the following?

A.A deficit of mass resulting from the creation of a hole in the lunar surface

presence of material from the impactor in the debris created by its impact

gradual cooling and stiffening of the Moon’s outer layer

ejection of massive amounts of debris from the Moon’s crust

rapid upwelling of material from the lunar mantle

Question 2

The passage suggests that if the scientists in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably

not formed early in the Moon’s history

not formed by the massive ejection of crustal debris

closely surrounded by other impact basins with anomalously low gravity

created by the impact of multiple large impactors

formed when the Moon was relatively elastic

Question 3

Which of the following best describes the organization of the passage?

anomalous finding is cited, the data used to support that finding are analyzed, and the finding is modified.

B.A theory about a phenomenon is introduced, data seeming to disprove that theory are analyzed, and the theory is rejected.

C.A phenomenon is described, a finding relating to the phenomenon is discussed, and a possible explanation for that finding is offered.

D.A debate among scientists regarding the explanation for a particular phenomenon is outlined, and one position in that debate is shown to be more persuasive.

observation of an astronomical event is described, and two schools of thought about