#16 - Comets do not give off their own light but reflect

[Administrator]

Complete Question Explanation

Must Be True-#%. The correct answer choice is (B)

In this scientific stimulus, the author tells us that scientists generally estimate the size of a comet based on the amount of light it reflects—the more light reflected, the bigger the comet. It has recently been determined, however, that Halley's comet reflects much less light per unit of mass than previously thought.

So, what are the implications of this recent discovery? If the material is less reflective, that means it takes more of that material than previously thought to reflect the amount of light Halley's reflects. So, Halley's comet must be bigger than previously thought.

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.

[niketown3000]

Hello,

I am confused why B is correct. I read it as though the greater the mass, the more light is reflected from a comet. Since the light reflect per unit mass went down, then then the mass has gone down by 60X. Therefore I chose C because it talked about less light coming.

-Neal

[Nikki Siclunov]

Hi Neal,

The material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought. Of course, the new discovery did not change the brightness of Halley's comet: it is just as bright now as it was before the discovery about its material. Now, if the brightness is the same, but the material reflects 60 times less light per unit of mass than had been previously thought, you'd need a lot more material to reflect the same amount of light. In other words, the total mass of the comet must be greater than previously thought.

Let me know if this makes sense.

[voodoochild]

PrepTest 7 - February 1993 LSAT Answers & Explanations - LR » Section #1

Question -

The question states that initially scientists thought that comets reflect light relative to their mass. However, the new satellite probe has determined that Halley's comet reflects 60 times less light than had been previously thought.

One of the interpretations is that :

Initially -

Mass | Brightness

1 unit | 1 unit (I am assuming 1:1 ratio)

Now

>1unit | 0.6 unit

Hence, the mass is more than what was thought previously.

However, another interpretation could be that :

1unit | 0.6 unit (i.e. the satellite probe helped to improve the measurement of the amount of light. Essentially, previously they were using a bad measuring device, but now they have satellite probes, which are better than the previous instruments.

In the second case, B) won't be correct.

Can anyone please help me?

Thanks
Voodoo

[Adam Tyson]

Think about how these scientists work; they take a known quantity and use it to calculate an unknown quantity. The known quantity here is the amount of light reflected by the comet. The unknown is the comet's mass. They know how much light is reflected - they can see it and measure it from here. What they estimated was the mass, but when their probes got there they discovered that their estimate was too low because the comet is less reflective than previously thought. The amount of reflected light is still a known quantity - what we learned by sending probes was that the comet is a lot bigger than previously thought. That's why B is correct and C is not.

[voodoochild]

Thanks for your response, Adam.

It's tricky because the question says that the scientists 'estimate' mass of a planet by its brightness. And while giving an example, after ":", they reversed the order. Essentially, "the greater a comet's mass, the more light that comet will reflect." This statement made me believe that the amount of light was better estimated.

That really confused me. On top of that, LSAT testmakers have planted an amazing trap for people like me! I think that they would have guessed it.

[GLMDYP]

Hi Powerscore!
For this question, I found both (B) and (E) are equally right. Can you explain why (B) is not right?
Thanks!

[David Boyle]

Hi Powerscore!
For this question, I found both (B) and (E) are equally right. Can you explain why (B) is not right?
Thanks!

Hello GLMDYP,

If this is the "comet" question, Feb. 1993 Logical Reasoning I, Section I: for all we know, scientists have all the info they need to estimate the mass of Halley's Comet. For (b), though, scientists "previously thought" that the material was 60 times brighter than it really is, so that it makes sense to assume they thought the mass was much lower. (They thought it was small and bright, so to speak, but really, it's big and dull!) So (b) is correct. (Did you mean, "Can you explain why (E) is not right?")

(If it's not the comet question...you may want to list some text from each question you post, so I know it's the right one.)

Hope that helps,
David

[eyeofthetiger]

Sorry, I still don't understand.

So let's say Halley 1, the old measurement, is 10 miles "big". And that it reflects 10 "rays" of light. Now, the probe finds a fraction for us, namely, that the comet reflects 60 times less light per unit of mass than previously thought. Let's call this new measurement Halley 2.

Doesn't this tell us that either: a) the mass stays the same, but we've learned that the comet reflects less, or b) that the new mass of the comet should now correspondingly decrease by the same multiplier of 60, thus making answer B wrong?

I know I'm missing something here, but can't wrap my head around it.

Any thoughts would be greatly appreciated.

[Nikki Siclunov]

Hey eyeofthetiger,

Thanks for the question! Here's what you might be missing: we still perceive the same amount of light being reflected as we did before the new estimate (the comet didn't suddenly become 60x dimmer). So, if each unit of mass reflects 60 times less light, but the total amount of light reflected remains the same, then we obviously need a lot more units of mass! Hence, the comet must be much larger than previously thought.

Does that clear things up?