Astronomer: In most cases in which a planet has been detected orbiting a distant star, the planet's orbit is distinct...

Mehran on October 10, 2017

Hi, no it's not a "Must Be True" question. It's a "Strengthen" question ("Which one of the following, if true, would most strengthen the astronomer's argument?").

Notice that the question stem is directing you to focus not on the text in the stimulus to find the right answer (which is often the case for Must Be True questions) but instead to the given answer choices (a hint that you're looking at a Strengthen question).

Hope this helps!

Minerva on September 13, 2019

Can someone please explain this question? Thanks!

Victoria on September 14, 2019

Hi @Minerva,

The astronomer concludes that "some of the planets in oval orbits around distant stars were probably thrown into those orbits by close encounters with other planets orbiting the same stars."

Why? Because, despite the fact that "the orbits of Earth and several other planets around our sun are approximately circular," most time when "a planet has been detected orbiting a distant star, the planet's orbit is distinctly oval," and "many comets orbiting our sun have been thrown into oval orbits by close encounters with planets orbiting our sun."

In this argument, the astronomer is trying to compare comets in our solar system with planets orbiting distant stars. We know that comets are thrown into oval orbits by close encounters with planets in our solar system and the astronomer uses this information to conclude that some of the planets orbiting distant stars in oval orbits were likely thrown into these orbits by close encounters with other planets in the system.

We are looking for the answer choice which strengthens the astronomer's ability to draw this conclusion.

Answer choice A is incorrect because it is irrelevant. The astronomer concludes that some planets were thrown into oval orbits by close encounters with other planets; the relative size of these planets does not matter.

Answer choice B is incorrect because we are not discussing planets in our solar system. The astronomer is using comets in our solar system to draw a comparison to planets in other solar systems. Therefore, the orbits of planets in our solar system have no bearing on the argument.

Answer choice D is incorrect because the astronomer claims that the change in orbit came from planets, specifically; not from some other object.

Answer choice E is incorrect because it weakens the argument. If there is no other object large enough to impact the planet's orbit, then it is impossible that the planet's orbit was impacted by other planets.

Answer choice C is correct because it strengthens the argument. If, in most cases in which planets have been discovered orbiting a distant star, there were no other planets orbiting the same star, it would be impossible for that planet's orbit to be impacted by other planets orbiting the same star as there are no other planets. Therefore, the fact that there are other planets strengthens the astronomer's conclusion that these other planets could have impacted the orbit of the oval-orbiting planet in a similar fashion to comets in our solar system.

Hope this helps! Please let us know if you have any further questions.