The conclusion is about a causal relation:

Space telescopes are better in one feature, and HENCE they will make earth telescopes obsolete.

Stating a negative feature of the space telescopes attacks this causal relation (though it may not directly attack the possibility that earth telescope will be obsoleted). Because space telescopes has a negative feature they will NOT be able to make the earth satellites obsolete.

If one considers "ground-based telescopes will soon become obsolete" the conclusion then your point is definitely valid. But if one considers "Superior feature of space telescope will cause ground-based telescopes to be obsolete", then option E is correct. In GMAT this causal relation as a conclusion is often tested.

For the same reason stated above option B is wrong. It does not attack the causal relation, but only supports why earth based telescopes may not be obsoleted. (Moreover, the condition that was used to prove that Space telescopes will replace earth telescopes, still holds good - even after mounting the telescopes on higher grounds, the distortion will not be eliminated, and hence the space telescopes still remain better of the two - nonetheless, this does not play any role in attacking the causal relation.)

I think we still need to do justice to this well-crafted question. Here's my attempt:

I'll just focus on options B, D, and E. However, before I get to the options, let me create a parallel argument.

Students of Class 9A are invariably ill-dressed. Students of Class 9B, however, are well-dressed. Therefore, students of Class 9A will never represent the school in inter-school competitions.

While this argument is not parallel to the original argument in every nuance, I believe it captures the essence of the original argument. If you do not agree, feel free to let me know.

Now, let me create parallel options for this argument:

Option B: Students of Class 9A mentored by their class-teacher do not have the kinds of dressing problems that make students look like beggars.

Does this option weaken the above argument?

The answer is NO. The reason is that this option says that some students of Class 9A (i.e. students mentored by the class-teacher) do not have some kinds of dressing problems. Okay. So, these students are probably better than other students of Class 9A in this respect. However, vis-a-vis students of Class 9B, are these students comparable? There is no indication of this comparison. The reasoning of the argument still holds as is. Even though these students do not have certain kinds of dressing problems, they still are ill-dressed, as originally stated in the argument. Thus, it still doesn't make any sense to ask these students to represent the school. Think about it. The reasoning in the argument was that students of Class 9A are shabby and students of Class 9B are not and that thus students of Class 9A will not represent the school. Even if some students of Class 9A are less shabby than some other students of Class 9A, all the students of Class 9A are still shabby, and thus the reasoning of the argument is still intact.

Similarly, the given option B just says that certain ground-based telescopes (i.e. located on mountain summits) do not have 'certain' kinds of distortions. However, they still have distortions as should every ground-based telescope have (given the facts in the passage). Thus, the reasoning of the argument still holds as is.

Option D (The Parallel form): When students of Class 9A are mentored by their class teacher, they become the best-dressed of the students of Class 9A.

Again, in this option too, just as in option B, we are comparing shabbiness or the sense of dressing among the students of Class 9A. We still are not presenting any advantage students of Class 9A have over students of Class 9B. Of course, if we rank some students of Class 9A in terms of their dressing sense, some students are going to come at the top. However, this doesn't have any effect on the given fact that all students of Class 9A are ill-dressed. Thus, the reasoning of the argument still stands as is.

Similarly, the given option D says that the telescopes located at high altitudes near the equator provide the best 'Earth-based' observations (not the best 'overall' - in which case this option will present an advantage of ground-based telescopes over space telescopes and thus will weaken the argument). Comparing different ground-based telescopes will not help; of course, some of them will be better than the others. However, they all are invariably inferior to the orbiting space telescopes, as stated in the passage. Thus, the reasoning of the passage holds as is.

Option E: This option presents a shortcoming of the orbiting space telescopes. Let me also state that this shortcoming is with respect to ground-based telescopes, not a shortcoming in general. Why do I say that this shortcoming is w.r.t ground-based telescopes?

Because of what the non-essential modifier(within double commas) means. The modifier means that the astronomers rely upon detailed spectral analyses for determining the chemical composition and evolutionary history of stars. If they rely on this capability for determining X (chemical composition etc), they must already be having this capability because, from the context, it seems that they are already determining the chemical composition and evolutionary history of stars. Now, if they have this capability and the orbiting space telescopes cannot provide this capability, it's likely that ground-based telescopes currently provide this capability. Thus, this option presents an advantage ground-based telescopes have over orbiting space telescopes and thus gives us a reason to doubt that ground-based telescopes will become obsolete.

I hope it helps!

- CJ
_________________

A student asked me to respond to this question, so . . .

1) Read question stem to determine question type.
Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?
We have a Weaken the Argument question.

2) Read passage and summarize premises and the conclusion.
PREMISE: Images from GBTs (ground-based telescopes) distorted by atmosphere
PREMISE: Space telescopes above atmosphere should make detailed images
CONCLUSION: GBTs to become obsolete for advanced research

3) Check the answer choices while reminding yourself of the CONCLUSION.

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.
Does this weaken the conclusion that GBTs will become obsolete for advanced research?
These project-management issues do NOT affect the conclusion.
ELIMINATE A

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.
In other words, high GBTs are better than low GBTs with regard to one particular phenomenon: the twinkling star effect.
Does this weaken the conclusion that GBTs will become obsolete for advanced research?
Not really. The reason for the soon-to-be demise of GBTs is that they suffer from atmospheric effects.
So, regardless of whether some GBTs are immune to ONE TYPE of atmospheric effect, the space telescopes are immune to ALL atmospheric effects.
ELIMINATE B

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.
This is similar to answer choice B.
In other words, SOME (well-placed) GBTs are better than other GBTs with regard to ONE particular atmospheric phenomenon: wind turbulence.
Does this weaken the conclusion that GBTs will become obsolete for advanced research?
ELIMINATE C (see answer choice B for rationale)

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.
This is similar to answer choices B & C.
Once again, we're told that SOME GBTs are better than other GBTs for a specific reason.
Does this weaken the conclusion that GBTs will become obsolete for advanced research?
No.
Answer choice D does not suggest that any GBTs are better suited than space telescopes are to study the universe.
ELIMINATE D

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.
Does this weaken the conclusion that GBTs will become obsolete for advanced research?
Yes!
If space telescopes are too small for certain research, then researches will still need some GBTs to perform the research described above.

Answer: E

Cheers,
Brent
_________________

saby1410, aritrar4, mk96, enigma1504 - Missed some tags to this question. Here is a detailed analysis. Hope you find it useful.

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere (in some way, whether winds, dust etc)

Orbiting space telescopes (above Earth's atmosphere) should provide superbly detailed images. Note the use of "should" - presumably because Earth's atmosphere does not interfere in their working. Does it actually happen, we don't know.

Conclusion: Ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

We need to weaken that ground based telescopes will become obsolete. They may have a disadvantage to space telescope but they may have some advantage too. Let's look at the options.

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

Irrelevant. There is no implication here that orbiting telescopes are far more expensive and difficult to launch. We are just told about this year's project is lagging while the project of ground telescope was on time and budget. We don't know what budget was allocated to each project.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

So one kind of atmospheric distortion (which makes stars appear to twinkle) can be taken care of by placing the ground based telescopes on mountain summits. But does this take care of all atmospheric distortions? Does it make ground based telescopes relevant? We don't know. So will ground based telescopes become obsolete? Can't say.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

So another kind of issue can be taken care of by carefully choosing location. So again, does this mean ground based telescope will stay relevant? Cannot say.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

How we get the best "Earth based observations" is irrelevant.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

A certain method which is used by astronomers to find data about stars requires telescope with more light gathering capacity than space telescopes. For at least this application then, ground telescopes will remain relevant. It is a method used by astronomers so it is reasonable to assume that ground based telescopes provide this facility. Else, how do the astronomers use detailed spectral analyses? After all, astronomers rely on it for determining the history of stars.
Hence it weakens that ground based telescopes will soon become obsolete for advanced astronomical research purposes.

Answer (E)
_________________

SOLUTION
Passage Analysis

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere.
• Telescopes based on land provide images that are distorted by the air around the earth.
Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images.
• Telescopes in space orbit the earth and work above the atmosphere. Therefore, they should give detailed images not distorted by the atmosphere.
Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.
• Thus, ground-based telescopes will stop being used for advanced research in astronomy.

Question stem Analysis
Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?
This is a weaken question stem. We should cast doubt on the conclusion that ground-based telescopes will become obsolete for advanced astronomical research.

Prethinking

Weaken framework
What new information can decrease one’s belief in the conclusion that that ground-based telescopes will become obsolete for advanced astronomical research, given that space telescope images are not distorted by the atmosphere and can give superbly detailed images?

Weakener 1- Ground-based telescopes have some advantages that space-based telescopes do not have which is relevant for advanced research.
Weakener 2- Space telescopes have some significant disadvantage that makes them not suitable for advanced research, despite the lack of atmospheric distortion

Option Analysis

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.
This statement points out only specific incidents and does not give any indication on why ground-based telescopes will not be obsolete. If space telescopes are more affordable then they should be at an advantage according to this option. Hence this is an incorrect answer.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.
This option says ground-based telescopes can evade atmospheric distortion of the type that leads to the twinkling of stars when placed on mountain summits. But we still do not know if all the atmospheric distortions can be avoided, we still do not know if placing these on summits will provide the superbly detailed images needed. Hence this option cannot weaken the claim as well.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.
Wind turbulence may not be the only factor that affects the image quality inside the atmosphere. Hence even if that is avoided, we cannot say the output will be at par with space telescopes. Hence this option is also incorrect.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.
This option specifies a particular location for a particular observation from the earth. But we need to compare ground telescope observations with space telescope observations to be relevant in this context. The absolute best earth-based observation may still be poorer than space-based observation. Hence this answer is incorrect.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.
Option E, in line with our weakener 2, provides a situation that is a disadvantage of space telescopes for the purpose of astronomical research.

The correct answer is E.
_________________

Choice B is talking about a particular kind of ground based telescope.(Ground based telescope located on mountains) You dont know how much percentage of Ground based telescope constitute those that are located on the mountains.

I think you are assuming that in near future, all the Ground based telescopes can be migrated to the mountains and hence can be useful. The option does not tell you this.

Also note that, if Space based telescope are already there which can carry out this functionality without any problems that ground based telescope may face, then why will the Ground based telescope be used if same functionality can be achieved by the space based ones .


See to weaken the conclusion, we need to show something that Ground based telescope can do but space based ones cannot, so there will be a reason to use ground based telescope as you cannot achieve that functionality using the space based.


Choice E precisely does that.


It states that Space based telescope may not be useful for analyzing chemical composition of stars .So it presents one drawback for space based telescope.

This functionality can be provided (we are not sure whether ground based can provide this functionality, but still there is a chance) by ground based telescope. So it weakens the conclusion.


We do not need to falsify a conclusion. Any choice that casts some doubt on the conclusion can be a valid Weakener

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.


The question says that ground-based telescope will soon become obsolete. The premise supporting this conclusion is "Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images."

To weaken this conclusion, we need to find any attribute of ground-based telescopes that is still advantageous and that use keeps it in astronomical research.

Option E does that, as this describes the fact that Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, can't be done with space telescopes as they don't have light gathering capacity.

Option B is out of consideration. It talks about possible location where it can work or where it can't work.

Dear Kahipz,

Answer choice B is incorrect.

Your thinking is partially correct:

"The problem with atmospheric distortion becomes abated, to whatever extent, when ground-based telescopes are located on mountain summits; hence, can still be of some use"

But did you went back to argument (specially try to correlate with point 2 below), which suggest that:

1. Images from ground-based telescopes are invariably distorted by the Earth's atmosphere

2. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images

Well, if you correlate the answer choice B with point number 02 above, you would certainly be unable to answer question why "Ground based telescopes are worse than orbiting space telescopes"

Answer choice literally means:

"Ground based telescopes are better when operated at the mountains as compared to when operated at ground"

Hope it helps.


"Please hit +1 kudos, if the explanation is helpful"

Thanks all for your helps.

As I practise more on CR, I start to develop an inkling as to why E is chosen instead of B, even though, reasoning-wise, I'm still not settled. I'd like to ask one more question though. About the wrong answer choice B, which category of incorrect answer would it fall into? Is it Out of Scope?

The response just above yours is a very good one.

Everything A is distorted by the atmosphere. Everything B operates outside the atmosphere. Therefore for advanced research, everything A will become obsolete. The second option is just saying that some As are better than other As. But the larger point is that any B is better than an A. The fact that some As are better than other As can't change that.
_________________

The point here is that no person above giving explanations prove that Ground telescopes are the ones that have more light-gathering capacity than the ones those are above Earth's atmosphere.

option E is ambiguous. IMO B
Lets say Ground telescopes- X
Space telescopes- Y
Light gathering telescopes- Z

Option E says Z is superior to Y but that doesn't support the cause for X not to be obsolete. If Z= X then E is true, but nowhere it is mentioned so.

Atleast option B says X cant be obsolete as they can be useful in some locations

Really not able to convince how option E is the correct answer.

we need to assume more to chose this.

Experts please help, why 'B' is wrong
_________________

The argument states that -
Orbiting telescopes provide more detailed images --> obsolescence of ground based telescopes for advanced astronomical research.

A - if one orbiting telescope exceeded its budget, does not mean that all such telescopes in the future will exceed their budgets. Also, what about other ground based telescopes? were they both within budget and on schedule?. Additionally, if orbiting telescopes are significantly cheaper than ground based telescopes, then this strengthens the argument.
B - but still they are in the atmospheric zone and are subject to at least some atmospheric distortions.
C - What about other distortions from the atmosphere?
D - "best earth based" is still not better than "space based".
E - Correct answer. Tells us about an important advantage that ground based telescopes have over space based telescopes, suggesting they might not get obsolete.
_________________

I am still not convinced on answer option E. The Answer option E would be true if the 'telescopes with more light gathering capacity" are "ground based telescopes". Since the answer E does not explicitly specify the same i chose B over E.

For a weakening / strengthening type question it not required to satisfy the "must be true" condition - a "could be" scenario would suffice. Option E states a negative point about space telescopes. In this case, highlighting a weakness of the space-based telescope is good enough to qualify the option as the weakening statement. Because of option E, it could be possible that the ground based telescopes would not be obsoleted (IF the ground based telescopes have more light gathering capacity). It is alright to add such conditions for a weakening / strengthening question.

For more explanation about choices B and E, please refer to the following post:

is-this-answer-key-from-og-correct-208210.html#p1715182

What happens here is that when we automatically see a weaken question we focus on just weakening the conclusion. Its important to understand the connection of why the author ended with his conclusion, in this case, the premise. The statement says: Therefore (conclusion indicator), ground based telescopes will soon become obsolete for advanced astronomical research purposes.

If you only focus on the part of "GB telescopes will soon become obsolete" and based it on the fact that its because of disorted images, then yes, you will fall for trap answer B.

But look more closely, it is saying it will become obsolete for a particular reason (it never says it will become completely obsolete) and that reason is for advanced astronomical research. So we need to look for an answer that states that the GB telescope is still needed for that research and that it has a unique quality that the space telescope does not have. And only answer E states that.

@gmatninja my issue with OA is that even though option E suggests that space telescopes have a drawback and cannot do a certain thing, it does not cast doubt on the argument that ground telescopes might become obsolete. maybe there would be a new kind of telescope/maybe even ground telescopes suck at that thing. We dont know!
is this not a very good quality QG question?

Here's the official explanation for reasoning:

The argument implicitly assumes that advanced astronomical research can be accomplished more effectively with the more
detailed, less distorted images produced by space telescopes and that therefore almost all advanced astronomical research will soon be conducted with space telescopes. This reasoning would be undermined by evidence that ground-based telescopes have substantial advantages for advanced astronomical research despite their distorted images or by evidence that space telescopes will not soon become common or affordable enough to support most advanced astronomical research.

Hope this helps. Thanks.

If you like this, click kudos.
_________________