Comets do not give off their own light but reflect light : GMAT Critical Reasoning (CR)
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# Comets do not give off their own light but reflect light

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Comets do not give off their own light but reflect light [#permalink]

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04 Feb 2008, 15:44
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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.
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04 Feb 2008, 16:00
B.
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04 Feb 2008, 16:18
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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.

(P1): Comets reflect light from other sources
(P2): Scientists estimate mass of comets by brightness (brighter = larger)
(P3): Halley's comet reflects 60% less light than originally thought (aka not as bright as originally thought)
(Conclusion): Halley's comet is bigger (has more mass) than originally estimated

B.
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04 Feb 2008, 18:14
B it seems...
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04 Feb 2008, 22:11
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.

IMO B.
Originally scientists estimated mass of the planet are proportional to the level of brightness. The more light comet reflects the more mass it has. But then, it was revealed that Halley comet reflects 60 times less light per unit of mass. Thus, mass should be more than it could be estimated from the brightness of the commet.
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22 May 2010, 05:16
az780 wrote:
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.

IMO B.
Originally scientists estimated mass of the planet are proportional to the level of brightness. The more light comet reflects the more mass it has. But then, it was revealed that Halley comet reflects 60 times less light per unit of mass. Thus, mass should be more than it could be estimated from the brightness of the commet.

I dont undestand this one. If Halley reflects less light than the one once had been thought, that means that Halley has less mass than once estimated, which is exactly the opposed as stated in B.
Could anybody shed some light?
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22 May 2010, 05:48
noboru,

In the passage, it says:
1. Light is in direct proportion with the mass of a comet.
2. The satellite probe contradited this relationship and shows that material of which Halley’s comet is composed reflects 60 times less light per unit of mass than had been previously thought. The numerical representation will be:
Earlier:
Light/Mass = 100 (say) = 1
Now,
Light/Mass < 100/(60x100) < 1/60 = 0.016

Both these figures are not same, i.e., the amount of light reflected is less now as compared to earlier studies. This implies that the mass should be more. So, the above relationship is in question.

This is what B says.
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Re: Comets do not give off their own light but reflect light [#permalink]

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27 Jan 2015, 11:43
Actually the amount of light does not change and now Halley reflects a 60 times less light for every ton of mass. So to reflect the same amount of light Halley's comet would have to be 60 times more massive than the scientists previously thought.

az780 wrote:
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.
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Re: Comets do not give off their own light but reflect light [#permalink]

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27 Jan 2015, 19:43
Please could somebody post the OA. Very interesting question. I picked the choice D.

az780 wrote:
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.

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Re: Comets do not give off their own light but reflect light   [#permalink] 27 Jan 2015, 19:43
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