QUESTION TYPE: Sufficient Assumption
CONCLUSION: Pluto is not a true planet.
REASONING: Pluto formed in orbit around Neptune.
ANALYSIS: You must prove that Pluto is not a planet. All we know about Pluto is that it formed in orbit around Neptune.
So the right answer must use that information. For example, we can assume that anything that formed in orbit around a planet can’t itself be a planet.
Many answers point out that Pluto was once a moon. That isn’t enough. Things can change. Those answers would need to say that something can’t be a planet if it was once a moon.
- Pluto was a moon when it was around Neptune. But it wouldn’t be a moon once it left Neptune’s orbit. So it wouldn’t have been simultaneously a moon and a planet.
- This is a necessary assumption. It proves that Pluto could be not a planet. But it doesn’t prove that Pluto is not a planet.
- This doesn’t matter. It’s like saying that if you never aged from the time you were 15 years old, you would still be a teenager. You did age, and Pluto did leave orbit. Things change.
- This doesn’t help us prove that Pluto isn’t a planet. It’s a fact about how we judge whether something is a planet, but it’s not definitive.
- CORRECT. Pluto didn’t form in orbit exclusively around the sun. Therefore, it’s not a planet.
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