LSAT Question Explanation
PT 108, Section 2, Question 20
Necessary AssumptionArgument structure
None of the comet's fragments made it to Jupiter's lower atmosphere and the comet was made of rock, not ice.
There was no water involved in the collisions.
Explanation
This argument is flawed. Just because there was no water in the collisions how are we supposed to know that the comet didn't make it to Jupiter's lower atmosphere and that the comet was made of rock?
The author is just assuming that water would have been involved if the comet made it to Jupiter's lower atmosphere or if the comet was made of ice.
Answer choices
This is certainly not necessary for the conclusion. In fact, it somewhat goes against the conclusion that the comet that crashed into Jupiter was made of rock.
This needs to be true for the argument to make sense. The author claims that the lack of water is evidence that the comets didn't make it to Jupiter's lower atmosphere. For that to be valid evidence we need to know that if they had made it to the lower atmosphere, water would have been involved.
It doesn't matter if rock or ice causes a larger explosion. This doesn't need to be true for the conclusion to hold, explosion size is irrelevant to the argument.
This doesn't need to be true for the conclusion that the fragments didn't make it to the lower atmosphere and were made of rock. They could differ in some ways, like size, and the conclusion wouldn't be affected.
This isn't needed for the conclusion, detectability doesn't affect if the fragments made it to the lower atmosphere or were made of rock vs. ice. We don't care how hard it is to detect various explosions on Jupiter. We detected the one in the stimulus.