Q15 - Astronomer: In most cases in which a planet

[mshinners]

Question Type:
Strengthen

Stimulus Breakdown:
Most planets outside our solar system have oval orbits, whereas our solar system's are circular. However, our solar system has comets with oval orbits caused by encounters with planets. So these other planets must have oval orbits for the same reason.

Answer Anticipation:
Since the argument relies on jumping from comets to planets, I'd expect an answer that strengthens that comparison - something relevant about planets and comets that makes them both able to have their orbits oval-ized by encounters with planets.

Correct answer:
(C)

Answer choice analysis:
(A) Out of scope. Even if we assume planets are always larger than comets (which I believe is a good assumption), this answer doesn't explain why the phenomenon we saw with comets applies to planets in other solar systems.

(B) Out of scope. There could be planets in our solar system with oval orbits - the stimulus just states that at least 3 have circular orbits.

(C) Bingo. This answer would probably take me a bit by surprise since I was expecting a similarity between comets and planets. Instead, this answer states that the cause (other planets) has been present in most instances where we saw the effect, which strengthens the argument. Additionally, this does fit into the criteria we established, since this tells us both comets and these exoplanets are similar in that they've both encountered other planets.

(D) Premise booster. This ups the statement in the stimulus from "many" to "most" but makes it more generic in stating the influence is "some other object" instead of a planet, specifically.

(E) Opposite (weaken). If these other planets don't have other objects (including planets) orbiting the stars, then the conclusion falls apart.

Takeaway/Pattern:
Stay loose when looking at answers, and consider anything that you can make even a loose argument for being in scope.

#officialexplanation

[layamaheshwari]

Can someone please explain why C is the correct answer? I had narrowed it down to B and D, so obviously I was way off the mark from the beginning.

[ohthatpatrick]

This came from JACKIEFIELDING, but it was posted in the wrong thread.
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Thought I'd give this explaining business a try!

Premise: In most cases, a planet orbiting a distant star has an oval orbit
Premise: But Earth and a few other planets around our sun are circular (not oval)
Premise: Sometimes comets around our sun are thrown into oval orbits from close encounters with other planets orbiting our sun

Conclusion: So some of those planets with oval orbits around distant stars probably also had a close encounter with another planet orbiting the same star

(Flaw: Just because that has happened to comets around our sun, doesn't ensure that it can apply to planets, or that it applies outside of our solar system to these distant stars/planets. But we aren't here to criticize, we're here to strengthen-- let's find a way to get at least a little more concrete support! Conclusion is essentially trying to say If Oval Orbit --> then must've had Close Encounter.)

On to the answer choices!

A) Usually the smaller of the two? We have no info about sizes of planets, and we don't care.

B) Remember in the stimulus that it says that the orbits of Earth and some (maybe just one!) of the other planets around our sun are circular; maybe there is a planet in our system that has a oval orbit, and if there's an oval orbit without a collision, then that certainly doesn't help the argument.

Just because none of the planets in our solar system have had close encounters, and some of them don't have oval orbits, that doesn't help to prove that collisions do cause oval orbits. (No one in my house has a cat, and some of us don't have rabies*, but that doesn't help the argument that everyone who has a cat will get rabies.)

C) Usually when there's a planet orbiting a distant star, there's another planet orbiting that same star? Great-- without another planet there, how would we get a close encounter with another planet, causing the oval orbit? Keep!

(Think about if this were not the case; if someone said that usually those distant planets are all on their lonesome. Then how the heck do they get a close encounter with another planet orbiting their same sun? That just broadens the mystery of the oval orbit, doesn't contribute to our argument.)

D) This switches the subject matter back to comets, which is not what our conclusion is concerned about, and also focuses on the comets orbiting around our sun, doesn't help us in explaining planets orbiting distant stars.

E) Ouch, this weakens the argument-- all of those distant stars with planets don't have any thing else big enough to affect their planet's orbit (so that means they don't have any planets that could have close encounters with each other, which would make their orbits oval-shaped). Wait, then how did these oval orbits come to be? Our conclusion was hoping the opposite, that these distant stars did have another planet in there with the first one, that's our whole theory about oval orbits!

*Note: actually, no one in my house has rabies Remember that "some" can include "all"!

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Great explanation!

I'll just add a little commentary. This argument, like so many, is just an author offering a causal explanation/hypothesis for some observed statistic or phenomenon.

PUZZLING PHENOMENON:
most distant planets have oval orbits whereas most local planets (in our solar system) have circular orbits.
(this seems to demand an explanation as to why OURS are circular or why THEIRS are ovular)

AUTHOR'S EXPLANATION:
The distant planets are flying close enough to another planet to end up with an ovular orbit.

This is one of the most common archetypes in LR, and there are two pressure points when you're evaluating an author's Explanation for / Interpretation of some stat or phenomenon:

1. How ELSE could we explain the evidence?
(on a strengthen question, we would pick an answer that RULES OUT an alternate explanation)

2. How PLAUSIBLE is the author's explanation?
(on a strengthen question, this is where you often see "covariance" answer choices showing "cause present, effect present" or "cause absent, effect absent")

So the correct answer (C) is super, duper weak in terms of doing anything. But it DOES relate to the plausibility of the author's explanation. It has more of the feel of a Necessary Assumption, because if (C) were NOT true, the author's hypothesis is garbage. It being true only mildly strengthens, but that's more than any other answer choices here do.

[ganbayou]

Hi
My question may not directly relate to the argument but...
Is our sun a star too??
not all planets orbit around something right? Only star I guess...And earth has almost circular means it did not encounter with planets orbiting the sun right?

[LukeM22]

This came from JACKIEFIELDING, but it was posted in the wrong thread.
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C) Usually when there's a planet orbiting a distant star, there's another planet orbiting that same star? Great-- without another planet there, how would we get a close encounter with another planet, causing the oval orbit? Keep!

(Think about if this were not the case; if someone said that usually those distant planets are all on their lonesome. Then how the heck do they get a close encounter with another planet orbiting their same sun? That just broadens the mystery of the oval orbit, doesn't contribute to our argument.)

But is the negation really "those distant planets are all on their lonesome"? This sounds a lot like the technical equivalent of "none of the planets have an additional planet"... which isn't the negation of the statement. The negation is "not most cases have an additional planet", which still allows for up to 50% of cases to have an additional planet, and therefore isn't mutually exclusive with the hypothesis, which means that the original statement isn't necessary. Are there any other reasons to pick this over D (which I concede isn't necessary either)?

[ohthatpatrick]

You're just judging Strengthen by the "perfect logic" standards of other questions. The correct answers to Strengthen and Weaken can be frustratingly mild in terms of effect.

But (C) definitely does do something to bolster the underlying possibility of the author's hypothesis taking place.

When planets don't have any buddy planets, the hypothesis is impossible.
So it's good to know that most of the ovular orbits are taking place in star systems where our author's hypothesis is eligible to occur.

What would we say (D) is doing that feels as good to know?

It's further convincing us that the oval orbits of comets came from near misses.The evidence told us that many times the oval orbit is caused by a near miss. (D) amps it up to "most of the time" the oval orbit is caused by a near miss.

But do we care? The author is trying to say that some oval orbits of planets came from near misses. Comets are brought up just to establish some plausibility to that hypothesis.

(C) is more directly discussing what we DON'T yet know .... is it plausible that the same causal mechanism that SOMETIMES affects comets could SOMETIMES affect planets?