ETS官方托福样题听力部分：天文课上的讨论

　　【ETS托福听力样题：a discussion in an astronomy class天文课上的讨论】ETS官方托福听力样题对托福备考阶段的考生具有非常重要的参考价值。通过样题可以迅速了解ETS的出题风格，和考试类型思路。

　　Narrator

　　Listen to part of a discussion in an astronomy class. The professor is discussing Pluto.

　　Professor

　　Well, today I thought we’d talk about some of the reasons why Pluto’s status as a planet has been debated. You see, until recently what makes a planet a planet was one of the simpler concepts in astronomy. It’s always been deemed so, uh…so obvious, so… basic that it was never officially defined…So anyway,…uh improvements in telescopes and related technology have led to a whole host of discoveries in our solar system…with one result being that now even the generally accepted idea of what a planet is is being challenged…or at least qualified. And this directly affects the status of Pluto.

　　Student A

　　So what makes Pluto so different that it could be, um…reclassified?

　　Professor

　　Well, actually, there are several important differences between Pluto and the other planets. First, when you look at the other planets, especially the planets in the outer solar system, where Pluto orbits, you see that Pluto stands out, it’s the oddball…and I’ll give you one guess why.

　　Student B

　　It’s gotta be the size…Jupiter, Saturn and uh, Uranus and Neptune,…they’re the gas giants, and, well, Pluto isn’t.

　　Professor

　　Exactly,…uh compared to the gas giants, Pluto’s very different,…it’s neither gaseous nor a giant. See, uh Pluto is less than half the size of the next smallest planet, Mercury. It’s even smaller than our moon…and smaller than other moons in our solar system. So Pluto is very small for a planet,…maybe it’s not large enough to be considered a planet.

　　Student A

　　But Pluto orbits the Sun and…I mean…well, that’s one of the things planets do.

　　Professor

　　You’re right…Most people agree that a planet orbits a sun, and Pluto certainly does that…every 248 years, but with a highly eccentric orbit. Take a look at this:

　　What I mean when I say ‘eccentric’ is…it’s not like the other planets’ orbits, instead it’s different in uh, two major ways. One, it’s elliptical, but the others are nearly circular. So for part of its orbit, Pluto is closer to the Sun than Neptune and for the rest it’s farther away. And two, Pluto orbits on a different plane. That is, all the planets orbit the Sun on the same plane, except Pluto…which orbits at a seventeen degree angle to the other orbits. Do you see where it looks like it crosses the other orbits?

　　Student A

　　[interrupting]

　　But I don’t see why being small and having an unusual orbit would change Pluto’s status. I mean it still has most of the features that the other planets have, doesn’t it? It’s got an atmosphere, granted it’s thin, but it’s there. It even has a moon!

　　Professor

　　That’s true. In fact, if it wasn’t for the discovery of the Kuiper belt rhymes with “piper”, there probably wouldn’t be a question about Pluto’s status….

　　[questioning sounds by the students]

　　Student B

　　It’s…I’m sorry, the what belt?

　　Professor

　　Uh, it’s the Kuiper belt.

　　It’s like a swarm of icy-rocky objects out beyond Neptune. It turns out that Kuiper belt objects, which are also called KBOs, have a lot in common with Pluto.

　　For one, KBOs and Pluto are made of the same stuff, namely rock and ice. And for most of its orbit, Pluto is in the Kuiper belt.

　　Remember when I said that Pluto has an eccentric orbit? Well, many KBOs do, too,…for the same reason,…their orbits are influenced by Neptune’s gravity. Now, without going into too much detail,…let me just say that Neptune’s gravity sort of pulls Pluto and the KBOs around…this results in orbits that are elliptical and almost exactly one and one half times longer than Neptune’s.

　　In light of these similarities, some suggest that Pluto’s merely the largest KBO found to date. Now, I’m saying this because several other large Kuiper belt objects have been found, some half as large as Pluto. Some scientists believe that they might find other KBOs as large as Pluto…

　　Student B

　　So you’re saying that Pluto’s more like a KBO than a planet?

　　Student A

　　Yeah…I mean, considering everything you just said, um, if Pluto were discovered today, would it even…well,…would it even be called a planet?

　　Professor

　　Well, let’s see. You tell me.

　　Student A

　　Hmmm, well…I’d still call it a planet. Like I said before…it may be small, but it’s got an atmosphere and a moon, it orbits the Sun and…

　　Student B

　　[interrupting]

　　Come on…it, it’s obviously a KBO. I mean, it’s in the Kuiper belt, it’s made of the same materials, it orbits the same way and it’s way smaller than any other planet. I think it’s clear

　　Professor

　　Well, nobody knew about the Kuiper belt when Pluto was discovered, so they called it a planet. But now? I think its status will continue to be questioned until there’s an official definition for planet.

　　24. What is the discussion mainly about?

　　Why most planets are larger than Pluto

　　The reasons some objects may soon be considered planets

　　How Pluto challenges the conventional idea of a planet

　　The discovery of Kuiper belt objects

　　25. How does the professor emphasize his point about Pluto’s size?

　　By stating the dimensions of nearby planets

　　By explaining the relationship between Pluto’s size and its orbit

　　By identifying the reasons why Pluto was originally misclassified

　　By comparing Pluto to other planets and objects in the solar system

　　26. What are two key features of Pluto’s orbit mentioned in the discussion?

　　Click on 2 answers.

　　Pluto’s orbit is influenced by Neptune’s gravity.

　　Pluto’s orbit is nearly circular.

　　Pluto’s orbit is at an angle to the other planets’ orbits.

　　Pluto’s orbit passes nearer to the Sun than most of the other planets.

　　27. According to the discussion, what are some reasons for NOT classifying Pluto as a planet?

　　Click on 3 answers.

　　It has an atmosphere.

　　It is located in the Kuiper belt.

　　It is composed of rock and ice.

　　It is located too far from the Sun.

　　It is much smaller than the other planets.