Comets do not give off their own light but reflect light from other so

Question

Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet’s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley’s comet is composed reflects 60 times less light per unit of mass than had been previously thought.

The statements above, if true, give the most support to which one of the following?

The statements above, if true, give the most support to which one of the following?

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley’s comet is composed.

(B) Previous estimates of the mass of Halley’s comet which were base on its brightness were too low.

(C) The total amount of light reflected from Halley’s comet is less than scientists had previously thought.

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.

(E) Scientists need more information before they can make a good estimate of the mass of Halley’s comet.

Bunuel · Accepted Answer

OFFICIAL EXPLANATION

(A) No. We can conclude nothing about any comets other than Halley’s comet.

(B) Yes.  The passage states that the amount of light reflected by a comet increases as its mass increases. From a measurement of a comet’s brightness, its mass is calculated. However, if Halley’s comet is less reflective than previously believed, it will take more mass than previously believed to reflect the measured amount of light.

(C) No. The amount of light reflected from the comet is measured from earth and does not change with the probe’s finding. However, the comet’s mass required to reflect this amount of light will need to be re-estimated.

(D) No. This is independent of the passage.

(E) No. This is independent of the passage. It is a good conclusion, though.

shrikant1512 · Answer

1+ for C 
B and C are close but "too low" in B is bit extreme.

Sent from my ONEPLUS A5000 using  GMAT Club Forum mobile app

abhinav770 · Answer

Conclusion Comets don't have their own light but reflect it from other light sources. A comet's mass is estimated by its brightness. Greater the mass - more light it would reflect off of itself. New revelation by the satellite probe: Haley's comet's material is composed of material which reflects the light many times LESS per unit mass than was previously thought. Hence, the Correct Answer: (B) EDIT: Corrected the error. I was wrong in choosing (B) over (C). Thank you Arro44 for the correct explanation. To read Arro44's detailed answer to this question click here . (Don't forget to drop a Kudos while you are there.

)

sudarshan22 · Answer

How is B the official answer to this question ? I opted for C over B for reasoning as mentioned above

Can anyone provide some insights on B ?

Arro44 · Answer

C is a trap my friends.

The scientists didnt make any judgements about the amount of light reflected, but rather derived their calculations of the comets mass from their observations.

As they now found out the comments material is less reflective than though, which does not change anything about the reflection they were able to decet, it is likely that the commet is around 60 times heavier than originally anticipated.

Hope this explains why it is B.

Best regards,
Chris

Akash720 · Answer

I still don't understand how the official answer is B.

Hi  Bunuel , do you have OE for the above question? Kindly provide your inputs. Thanks !

Posted from my mobile device

Arro44 · Answer

OE from LSAT forum: https://forum.powerscore.com/lsat/viewtopic.php?t=1804 Answer choice (A): Halley's is 60 times less reflective than previously thought, but that doesn't mean that there are materials exactly 60 times as reflective. Answer choice (B): This is the correct answer choice. If it takes more Halley's material to reflect the amount of light that we've seen, then Halley's must be bigger than we thought. In other words, previous estimates were too low. Answer choice (C): The point of the stimulus is not that Halley's reflects less light than we thought. Rather, it reflected a certain amount of light, which, as it turns out, requires more Halley's material to reflect. Answer choice (D): There is no such comparison from comet to comet in the stimulus, so this answer choice is not supported by the author. The only referenced variation is between what we used to believe Halley's mass to be, and what recent discoveries suggest today about Halley's mass. Answer choice (E): This stimulus presents a recent discovery that seems to provide the basis for a good estimate, so this answer choice is unsupported by the stimulus and incorrect.

rahulkashyap · Answer

how it may be b is that...
think of the total light reflected as 600 units.
lets say they thought that this comet was made of material A, which has a light density of 60units/ kg
this would mean that it weighed 600/60= 10 kgs according to older calculations

now they have discovered that the actual light density is 60/60= 1unit/kg
the total light reflected still remains the same, i.e. 600 units
with the new density, the weight is now 600/1 = 600kgs according to new calculation

Akash720 · Answer

Thanks Chris !

This one was really confusing but now it's clear.

sudarshan22 · Answer

Ohh that way! Now I get it. But, questions like these may penalize you on D-Day when you see the word " Too low " in option B and zero out the option, GMAT why you no easy?

Thanks for the explanation rahulkashyap What would I do without nice people like you who offers such selfless help on the forum

nightblade354 · Answer

The key here is the wording, since you are not given a conclusion.

Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet’s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley’s comet is composed reflects 60 times less light per unit of mass than had been previously thought.

The statements above, if true, give the most support to which one of the following?

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley’s comet is composed.

(B) Previous estimates of the mass of Halley’s comet which were base on its brightness were too low.

(C) The total amount of light reflected from Halley’s comet is less than scientists had previously thought.

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.

(E) Scientists need more information before they can make a good estimate of the mass of Halley’s comet.

To diagram:  More light -- More mass
 Less brightness per unit of mass -- less mass per unit than originally thought -- same amount of mass -- less dense material -- brightness unchanged

Great question

rohanrale · Answer

Here brightness is linked with the comet's mass - the greater a comet’s mass, the more light that comet will reflect.

Latest evidence - the material of which Halley’s comet is composed reflects 60 times less light per unit of mass than had been previously thought.

So Halley's comet reflects less light because of the materials of which it is composed. So the estimates of the mass of the Halley's comet based of the reflection of light principle are not correct. The mass of the Halley's comet has to be greater than previously calculated.

Only option B discusses this issue correctly, so B is the answer.

suminha · Answer

The key here is <> Means light/mass is 60 times less than previously thought. Means either amount of light(numerator) was smaller than they thoght or the mass (denominator) was bigger than they thought. Voilà (B) is telling you that the denominator was actually bigger than they thought. Do not fall for (C) “total amount of light”. The passage lends only about the amount of light/mass. Posted from my mobile device

shrgmat · Answer

I am not really sure of studying a question like this one. Why can't the brightness change and amount of light emitted be less? Where exactly within the prompt does it say that brightness is the same? It doesn't.

So, we are to ASSUME that based on "Scientists estimate the mass of comets by their brightness..".

So, giving us a bad question with incomplete information, makes this a hard qn - really? Whatever..

prantik_BW · Answer

i can understand b and c are both correct how to eliminate c as if you agree with reduced mass then light emit should be less and vice e versa here it is given in passage "has revealed that the material of which Halley???s comet is composed reflects 60 times less light per unit of mass than had been previously thought." there would be a perviosly thought mass which is now reduced so as light emit per mass is reduced if mass is not increasing and per unit light is decreasing how will not total light reflecting will not decrease

MartyMurray · Answer

Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet’s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley’s comet is composed reflects 60 times less light per unit of mass than had been previously thought.

The statements above, if true, give the most support to which one of the following?

The statements above, if true, give the most support to which one of the following?

This is a Conclusion question, and the correct answer will logically follow from something said by the passage.

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley’s comet is composed.

The passage says nothing that supports this choice.

In fact, the fact that the material of which Halley's comet is composed does not reflect that much light indicates that it's possible that no comet is composed of material that reflects that much light.

Eliminate.

(B) Previous estimates of the mass of Halley’s comet which were based on its brightness were too low.

This choice is logically supported by the passage. Here's how.

Scientists estimated the mass of Halley's comet using the amount of light reflected by the comet. To do so, they measured the amount of light reflected and divided that by the estimated amount of light reflected per unit of mass to get the mass.

So, they used the following:

Light/Light Reflected Per Unit of Mass = Mass

The passage indicates that they had overestimated Light Reflected Per Unit of Mass.

So, we can see that, since Light Reflected Per Unit of Mass is the denominator, overestimating Light Reflected Per Unit of Mass would result in an underestimation of Mass.

Keep.

(C) The total amount of light reflected from Halley’s comet is less than scientists had previously thought.

This is a trap choice.

The point of the passage is that the material of which Halley's comet is composed is not as reflective as scientists had thought.

That doesn't mean that they had overestimated the total amount of light reflected by the comet. It makes sense that scientists can observe from a distance how much light is reflected in total.

What's apparently difficult is knowing how reflective the comet is.

For example, a large comet that is not very reflective will reflect the same total amount of light as a more reflective, smaller comet does. So, from a distance, it could be difficult to tell which Halley's comet is, a not very reflective, large comet or a smaller, more reflective comet.

So, what the passage indicates is that scientists can get the reflectivity, and thus the size, of a comet wrong, not that they got the total amount of light reflected by Halley's comet wrong.

Eliminate.

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.

This is plausible, but the passage does not say anything that supports it.

Eliminate.

(E) Scientists need more information before they can make a good estimate of the mass of Halley’s comet.

In a way, this contradicts what the passage says.

After all, if the information provided by the satellite probe is accurate, then scientist may now have information sufficient for making a good estimate of the mass of Halley's comet.

In any case, the passage does not say anything that clearly indicates that scientist need more information to make a good estimate. It indicates only that a previous estimate was incorrect.

Eliminate.

Correct answer:   B

lewdtoucan · Answer

Hello, I chose option C for this as well, but when here is how I reasoned my way to option B.

Based on the info in the statement, we can say that 
total light emitted = (light per unit mass) * (total mass)

The statement says that the light per unit mass is much lower than previously estimated.

Evaluating option A: Incorrect because it compares two different comets while the statement only talks about Halley's Comet and general characteristics of a comet.

Option B: if we express the equation above such that we have mass on the LHS, we can see that the previous estimate for the mass was too low (because the denominator-- light per unit mass was higher) compared to the recent estimate. Correct

Option C: to make a conclusion about the total amount of light, we need information about the total mass of the comet, which the statement does not provide. So this inference is not fully supported.

Option D: Incorrect. Like A, D compares properties of two different comets.

Option E: I had a tough time eliminating this choice. From the equation above, to fully conclude on the mass of the comet we also need information about the total light, which is not presented in the statement. But in the absence of that information, if we assume that the total light has not changed, then we can eliminate this choice because there is sufficient information to make a conclusion about the mass of the comet.

Please feel free to correct me if my reasoning is flawed. I think my reasoning for eliminating E is not as solid as I'd like it to be.

Comets do not give off their own light but reflect light from other so

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Comets do not give off their own light but reflect light from other so

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