Although Pluto has an atmosphere and is much larger than any asteroid

Question

Although Pluto has an atmosphere and is much larger than any asteroid, Pluto is not a true planet. Pluto formed in orbit around the planet Neptune and was then ejected from orbit around Neptune when Triton, Neptune's largest moon, was captured by Neptune's gravity.

The conclusion of the argument follows logically if which one of the following is assumed?

(A) No celestial body can simultaneously be a moon and a planet.
(B) Not all celestial bodies that have an atmosphere and orbit the sun are true planets.
(C) If Pluto had not been ejected from its orbit around Neptune, Pluto would not have its current orbit around the sun and would still be a moon.
(D) The size of a celestial body in orbit around the sun is not relevant to determining whether or not it is a true planet.
(E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.

Source: LSAT

generis · Accepted Answer

NOTE: If you want only POE plus why (E) is correct, scroll down. POE is labeled.

warrior1991  , answer E is the missing puzzle piece. It would be almost impossible to "pre-think" the answer.

As I read this prompt, I thought, "Too much information. 
Too many possible logical relationships.
What the h*ll does a moon's being captured by Neptune's gravity have to do with anything?"

Let the answer choices sort out
information, logical relationships, and  which part of this prompt matters .

Only this part ends up mattering: "Pluto formed in orbit around Neptune."
(Pluto  was  formed while it orbited around Neptune.)

• Straight logic: (E) works perfectly.

E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.

If X is a true planet, then X formed in orbit around the sun and only the sun.

Pluto did not form in orbit around the sun.
Pluto formed in orbit around  Neptune. 
Because Pluto did not form in orbit around the sun exclusively,
Pluto cannot be a true planet.
That last statement is the conclusion.

This assumption led to that conclusion. 
Answer E is correct.

• Breaking down the prompt: (E) gets us to the conclusion.

Note: we can infer a factual statement, a premise, from part of this conclusion.

Conclusion: Pluto is not a planet

Fact #1 : 
At the least, a true planet has an atmosphere and is bigger than an asteroid. 
→ Pluto has an atmosphere and is bigger than an asteroid but is not a planet. 
Something is missing or something extra is illegal.
We infer Fact #1 from " Although  Pluto has X and Y  ..."

Fact #2 : Pluto formed in orbit around Neptune

Fact #3 : Pluto was ejected from Neptune's orbit

In terms of "what ingredients equal a PLANET,"
what is missing? Or what extra thing is illegal?

(E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.

Ah. The missing piece. 
Three ingredients (at least) constitute a planet.
-- The body (1) has an atmosphere, (2) is bigger than an asteroid, and (3)  is formed in orbit around the sun exclusively. 
Pluto has the first two ingredients.

Ingredient #3? No.
Pluto formed in orbit around Neptune.
Pluto did not form in orbit around the sun.
Pluto lacks a key ingredient: formation in orbit around the sun exclusively.
Therefore, Pluto is not a true planet.

Conclusion proven. (E) is correct.

• POE

(A) No celestial body can simultaneously be a moon and a planet.
 Irrelevant.  Prompt says nothing about whether Pluto is a moon.

(B) Not all celestial bodies that have an atmosphere and orbit the sun are true planets.
 Irrelevant OR assumes what it is trying to prove (that the conclusion is true).

-- IRRELEVANT: nothing in the prompt says that Pluto now orbits the sun.
Pluto could have been ejected from Neptune's orbit 
and sucked into the orbit of Uranus, for all we know.
I would stop here and eliminate B. Many aspirants will not be comfortable with that move.

-- Assumes the truth of the conclusion rather than proves the truth of the conclusion: 
The conclusion  to be proven  is that Pluto is not a planet.

Do not assume that Pluto is NOT a planet.

Pluto has an atmosphere. Assume that Pluto orbits the sun. (Again, I'm not willing to go this far.)
We do not know whether Pluto is or is not a planet.

IF the conclusion is true, then maybe we can utter statement (B).
 IF Pluto is not a planet , then we know
that at least one celestial body has an atmosphere, orbits the sun, and is not a planet.

But an assumption   cannot assume  that the conclusion is true. 
An assumption  helps prove  that the conclusion is true.

This option does hint that the  sun  might be important.

(C) If Pluto had not been ejected from its orbit around Neptune, Pluto would not have its current orbit around the sun and  would still be a moon. 
 Off topic.  
We have no idea whether Pluto was a moon. Ignore the rest of the answer because
"Pluto was a moon" is not a given fact.

(D) The size of a celestial body in orbit around the sun is not relevant to determining whether or not it is a true planet.
 Counterfactual or irrelevant. 
-- Counterfactual: size IS relevant. 
We can infer from the FACTUAL phrase "although Pluto has an atmosphere and is bigger than an asteroid"
that a true planet is bigger than an asteroid.
If something had not gone wrong with Pluto, it would indeed be a planet.
Size DOES matter. (D) is counterfactual and does not help to prove the conclusion.

-- irrelevant. 
Okay. Size is not relevant. That fact does not prove that Pluto is NOT a planet.
If size is not relevant, then  whatever  size Pluto is does not matter.
"Size is not relevant" does NOT prove that Pluto is not a planet.

(E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.
By POE, we are left with E.

This statement works. Its content is exactly what we are missing.

ASSUMPTION THAT IS TRUE: 
 If a celestial body is a true planet, then it formed in orbit around the sun and only the sun. 
Pluto formed in orbit around Neptune.
Pluto did not form in orbit around the sun.
 Pluto cannot be a true planet because it did NOT form in orbit around the sun.

True planets must have been  formed  in orbit around the sun exclusively.
 Pluto, which formed in orbit around Neptune, is not a true planet. 
That's the conclusion.

Option E is the correct answer.

Hope that helps.

KarishmaB · Answer

Pluto has an atmosphere and is much larger than any asteroid (some characteristics of a planet)
Pluto formed in orbit around the planet Neptune and was then ejected (supports Pluto is not a planet)

Conclusion: Pluto is not a true planet.

What will help us establish that Pluto is not a true planet.

We are looking for an assumption (a missing necessary premise) which will help us establish the conclusion. Which of the options should we add to our argument so that we can conclude that Pluto is indeed not a planet?

(A) No celestial body can simultaneously be a moon and a planet.

Pluto is not a moon now. This doesn't tell us why it cannot be a planet.

(B) Not all celestial bodies that have an atmosphere and orbit the sun are true planets.

Doesn't tell us why Pluto cannot be a planet. What characteristics ensure that it is not a planet.

(C) If Pluto had not been ejected from its orbit around Neptune, Pluto would not have its current orbit around the sun and would still be a moon.

Even if this were true, Pluto did get ejected from its orbit and is not a moon now. How can we say that it cannot be a planet now?

(D) The size of a celestial body in orbit around the sun is not relevant to determining whether or not it is a true planet.

The question is what determines whether a celestial body is a true planet.

(E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.

Perfect. If we are given that to be a true planet, the body must have formed in orbit around the sun, then we can say for sure that Pluto is not a true planet. Let's add this to our argument and see if our conclusion can be drawn now.

Pluto has an atmosphere and is much larger than any asteroid.
Pluto formed in orbit around the planet Neptune and was then ejected. 
For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.

Conclusion: Pluto is not a true planet.

Correct. We can conclude our conclusion now.

chetan2u · Answer

hi..
reason why C and other choices are incorrect and E is correct..

(A) No celestial body can simultaneously be a moon and a planet.
 pluto is NOT both moon and planet.... so out

(B) Not all celestial bodies that have an atmosphere and orbit the sun are true planets.
 conclusion itself says that pluto has an atmosphere and if you negate this doesnt help the reasoning

(C) If Pluto had not been ejected from its orbit around Neptune, Pluto would not have its current orbit around the sun and would still be a moon.
 SO WHAT!!! we are talking of WHY Pluto is not a true planet although it has the characteristics of a planet. and this doesn't help in it at all.

(D) The size of a celestial body in orbit around the sun is not relevant to determining whether or not it is a true planet.
 Size is mentioned in conclusion but not a criteria in reasoning

(E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.
   "Pluto formed in orbit around the planet Neptune and was then ejected from orbit around Neptune" is mentioned and then it is said that Pluto is not a planet. so it means any celestial body not formed in orbit around sun from very beginning is not to be considered a planet   ... TRUE

E

gmatexam439 · Answer

Although Pluto has an atmosphere and is much larger than any asteroid, Pluto is not a true planet. Pluto formed in orbit around the planet Neptune and was then ejected from orbit around Neptune when Triton, Neptune's largest moon, was captured by Neptune's gravity.

The conclusion of the argument follows logically if which one of the following is assumed?

(A) No celestial body can simultaneously be a moon and a planet. - The passage doesn't state that Pluto was a moon 
(B) Not all celestial bodies that have an atmosphere and orbit the sun are true planets. - This is just a fact statement. 
(C) If Pluto had not been ejected from its orbit around Neptune, Pluto would not have its current orbit around the sun and would still be a moon. - This is a hypothetical situation, not talked about in the passage. 
(D) The size of a celestial body in orbit around the sun is not relevant to determining whether or not it is a true planet. - This is opposite of the premise, which compares the size of Pluto to that of an asteroid. 
(E) For a celestial body to be a true planet it must have formed in orbit around the sun exclusively. - Correct. If Pluto wasn't Neptune's part, it would have been a true planet

warrior1991 · Answer

generis   GMATNinja   VeritasKarishma

Could you help how E is correct??

ballest127 · Answer

Hi VeritasKarishma,

Thank you for your kind explanation.

However, I have a doubt on E.

As you stated, 
"
Pluto has an atmosphere and is much larger than any asteroid.
Pluto formed in orbit around the planet Neptune and was  then ejected .
For a celestial body to be a true planet it must have formed in orbit around the sun exclusively.
"
it can be seen that Pluto was later ejected; it did not orbit around the Pluto since then.
However, how can we be sure that it did not simultaneously orbit the Sun and Pluto, and once it did not orbit around Pluto then it exclusively orbit around the Sun.

If this is the case, then the conclusion is not true.

So why E is correct?

Please explain.

Thank you.

aniket16c · Answer

If I may help:

The choice states that a true planet must have   formed in orbit around the sun exclusively .
Exclusively means - to the exclusion of others; only; solely.
Means the celestial body right from the time it has formed must be orbiting  sun only and no other planet .
Hence, as far as I can understand, we cannot count the bodies as true planets that either simultaneously orbit around two objects as true planets or later orbit around the sun

Pankaj0901 · Answer

Is the prompt slightly different from the "necessary assumptions" questions, in terms of what we should look for in the correct answer?
 The conclusion of the argument follows logically if which one of the following is assumed? 
 AndrewN  - There is new information (orbits around the sun exclusively, while the passage doesn't talk about Sun at all) in the correct answer choice E that MUST hold true for the conclusion to hold.

AndrewN · Answer

You are correct,  Pankaj0901 . This question takes certain liberties in its phrasing and answer choices that we would not expect to see on the GMAT™. A few Experts have chimed in above, so if you are interested in an analysis of the question, there you go. I simply do not think the question is worth studying for GMAT™ preparation purposes.

On a related note, I was pleased to see that  RonPurewal  recently decided to resurface on GMAT Club. In response to  another quite difficult LSAT Logical Reasoning question , he wrote the following:

I think this is a somewhat divisive issue among GMAT™ tutors and teachers, whether to supplement with LSAT material, with people whose opinions I hold in high esteem taking either side.

Thank you for thinking to ask.

- Andrew

jgs2sin · Answer

There is no mention of the sun in the passage. Though its logical its the sun, do we assume it since most answer have the sun in it?

KarishmaB · Answer

Yes, certainly. B schools do expect that everyone in their class would have a certain basic level of verbal and general awareness. Ask yourself this - would you expect EVERY classmate of yours in a B school to know this, irrespective of what his academic background and geographical location? If yes, then it doesn't need to be explicitly mentioned.

MartyMurray · Answer

We can use common knowledge in answering CR questions. So, facts such as that water is wet or gravity pulls objects toward the center of a planet can be used.

That said, the way this question works goes beyond how GMAT CR questions normally work, and this question isn't great.

For one thing, while the information we have indicates that Pluto didn't form in orbit around the Sun exclusively, it's not clear from what the passage says that "For a celestial body to be a true planet it must have formed in orbit around the sun exclusively." After all, it could be that a planet could form of material ejected from the Sun or could start forming elsewhere before it begins orbiting the Sun.

All the passage says is that "Pluto formed in orbit around the planet Neptune." OK, but there are many ways other than "formed in orbit around the planet Neptune" that are not "formed in orbit around the Sun."

So, this question is not a good question no matter what test it's from.

VerbalBot · Answer

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Although Pluto has an atmosphere and is much larger than any asteroid

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Although Pluto has an atmosphere and is much larger than any asteroid

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