Although Pluto has an atmosphere and is much larger than any asteroid, Pluto is not a true planet. Pluto formed in or...

shafieiava on March 19, 2020


I didnt end up choosing an answer choice E because the passage just tells us about orbit, not necessarily orbiting around a sun... I thought perhaps we could be talking about orbiting moons or another planet. Can someone explain why the correct answer is correct when there is no direct mention of the sun in the passage?

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SamA on March 19, 2020

Hello @shafieiava,

The author concludes that Pluto is not a planet. Why? Because it formed in orbit around Neptune and was later ejected from that orbit.

Here's the problem. The author presents us with no definition of a planet. How do I know that forming in Neptune's orbit prohibits designation as a planet? There is something missing in this argument. We need to provide the missing link in the form of an assumption. The correct answer will guarantee the truth of the conclusion. We are looking for an answer choice which confirms that Pluto is not a planet.

Let's talk about E. You are correct that the passage never mentions the sun. However, we know that Pluto formed in orbit around Neptune. Therefore, we know that it did not form around the sun exclusively. Think of the sufficient and necessary conditions.

E: Planet ------> Formed Around Sun Exclusively

Pluto did not meet the necessary condition. Therefore it is not a planet.