One of the most important events for modern astronomy was the series o

A larger explosion would occur upon collision with Jupiter if Shoemaker-Levy 9 were composed of rock than if it were composed of ice. What does this double subjunctive mean "if Shoemaker-Levy 9 were composed of rock than if it were composed of ice".

Hi Sajjad1994,

Request you to please OE for this question.

CONCLUSION - None of the comet's fragments penetrated Jupiter's lower atmosphere and Comet was composed of rocks rather than ice

PRE THINKING -

IN WHAT SCENARIO - Comet's fragments entered Jupiter's lower atmosphere and Comet was composed of ice

GIVEN -

1) Series of collisions happened in 1994, >12 large objects with Jupiter
2) Collision showed no signs of water
3) No water was involved in the collisions

ANSWER CHOICE ANALYSIS -

A) Asteroids not talked of in the argument
B) CORRECT - Must be true in order for conclusion to hold true
C) Intensity of collision not mentioned in the argument
D) Whether the composition is same or different doesn't matter
E) Detection from earth not talked about

Hello Sajjad,

Here, isn't option B an answer to must be true question. How is the assumption regarding comet that penetrated lower atmosphere would have water helping a conclusion that if not lower atmosphere, then no water.

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Assumption and conclusion are closely inter-related but are in reverse order, Conclusion is made after setting up an assumption. Argument of this question contains conclusion and we have to find the assumption.

There are two conditions that support that there was no water involved in the collisions:
1. none of the comet???s fragments penetrated to Jupiter???s lower atmosphere
2. the comet was composed of rock rather than ice.

Option B covers ONLY the 1st point. Does B need to be NECESSARILY TRUE? What if B is not true and the second condition "the comet was composed of rock rather than ice" holds. We would not need option B as the assumption in that case.

Can someone please highlight what I am missing?

Understanding the argument -
One of the most important events for modern astronomy was the series of collisions, during a single week in 1994, of more than a dozen large objects with Jupiter. Fact
The collision of these objects, which once formed most of the comet Shoemaker-Levy 9, resulted in formations that showed no signs of water. Fact
There was thus no water involved in the collisions, so we know that none of the comet’s fragments penetrated to Jupiter’s lower atmosphere and that the comet was composed of rock rather than ice. Let's break it.
- thus no water involved in the collisions - Intermediate conclusion.
- So two things
1. None of the comet’s fragments penetrated to Jupiter’s lower atmosphere
2. The comet was composed of rock rather than ice

Option Elimination - We need to find a minimum condition or a missing premise for the conclusion to hold true.

(A) Comets tend to be composed largely of ice while asteroids are composed mainly of rock. - at best, it's a weakener because, in the conclusion, we said the comet was composed of rock, while this option says that comets are composed mainly of ice. Opposite of what we need.

(B) If Jupiter’s lower atmosphere had been penetrated by the comet’s fragments, the resulting formations would show signs of water. - We need this for the conclusion to hold, which is "None of the comet’s fragments penetrated to Jupiter’s lower atmosphere" because had they penetrated the lower atmosphere, they would have shown signs of water (don't let your wild imaginations come into the picture as to how come Jupiter's lower atmosphere has water? That knowledge is outside the scope of this argument). And if we want to negate the option, we negate the main clause, "the resulting formations would show signs of water." So the negation will be "If Jupiter’s lower atmosphere had been penetrated by the comet’s fragments, the resulting formations would not show signs of water." Then, the conclusion is shattered.

(C) A larger explosion would occur upon collision with Jupiter if Shoemaker-Levy 9 were composed of rock than if it were composed of ice. - Do we know if the explosion in the argument was larger or smaller? We don't know. Even if we assume that the rock explosion would be larger then at best, this weakens.

(D) The post-collision analysis of Jupiter showed that the formations all had exactly the same composition. - We just wanted to know whether it had water or not. If the formations are of the same composition, i.e., the same hydrogen %age or the same X mineral %age, how does that matter to the conclusion? Out of scope.

(E) The deeper the explosion occurred in Jupiter’s atmosphere, the more difficult it would be to detect from Earth. - This raises doubts about whether our conclusion that it didn't penetrate the lower layers is proper. Maybe it was difficult to detect the deeper the explosion, so it is possible that it penetrated the lower atmosphere, but we couldn't detect it. So at best, it's a weakener.