17-Q35 to Q37:月球表面上的洞

hollyball

17-Q35 to Q37:月球表面上的洞

(This passage was excerpted from material

published in 1996.)

 

      When a large body strikes a planet

          or moon, material is ejected, thereby

          creating a hole in the planet and a local

Line
               deficit of mass.  This deficit shows up

  (5)          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

areas.  One would therefore expect that

 (10)   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

 (15)   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

 (20)   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

 (25)   beneath the impactors almost imme-

diately, compensating for the ejected

material and thus leaving no low gravity

anomaly in the resulting basin.  Later,

however, as the Moon grew cooler

 (30)   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.

Q36:

The passage suggests that if the scientists mentioned in line 19 are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably

             

A.       were not formed early in the Moon’s history

B.       were not formed by the massive ejection of crustal debris

C.       are closely surrounded by other impact basins with anomalously low gravity

D.      were created by the impact of multiple large impactors

E.       were formed when the Moon was relatively elastic

 

这道题把我弄混了,本来认为应该有negative gravity anomalies,但是实施没有,科学家推断早期,,,可是后来later,however,,,,

按照逻辑应该是说早期有,但是后来随着温度,弹性什么的,所以才没有了,可是这个逻辑对么,请大家指正!!!

 

还有,请问这句话是什么意思 leaving no low gravity

anomaly in the resulting basin.

 

多谢大家!!!!多谢多谢了

anomaly in the resulting basin.

 

多谢大家!!!!多谢多谢了

 

 

cyoasis

同问，A是什么意思啊？

spongebobmn

今天正好看到这一篇，就来凑个热闹。
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.
这段话的意思是，当有大家伙撞击月球表面，造成大量月表（月壳）物质抛射出来。（按前文的理论，撞击区由于损失了质量，会造成局部引力减小）。但（由于月球早期较热，较有弹性）密度更大的月幔迅速上升补充了被抛射的物质，（所以局部质量不会减小，反而有可能比撞击前增加），所以在撞击（形成的）盆地里就没有引力异常减小的情况。
后文有说后来月球变冷，弹性减弱，这样（月幔）上升补充月表的程度就不如以前。而现在月壳又冷又硬，再有撞击的话，这种（月幔上升带来的）引力补偿就不太会有了。这里其实暗示在月球形成早期，月球热，弹性强。引力补偿很常见。
36题问“the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably”。如果盆地表现出强烈的引力减小异常，那末说明引力补偿没有发生。所以撞击不太会发生在月史早期（A)。
答案E说的正好相反，如果月球还相对由弹性的话，那么引力补偿或多或少都会发生。就不会有“most significant negative gravity anomalies”了。

yinglizzy

很清晰，谢谢！！