- A
- B
- C
Listen to a lecture in an astronomy class, take detailed notes while listening.
erratic – changing irregularly; not predictable
orbit – to move around a larger object in space
overlap – to extend over and cover a part of an object
strict – severe; precise
unobstructed – not blocked by other things
Fill in the following diagram.
Criteria
Pluto
A 1.
A 2.
B 3.
B 4.
C 5.
C 6.
Now answer the questions using your notes.
Why Pluto is No Longer a Planet
Summarize the text using your notes and diagram.
- 1: Must orbit the sun.
- 2: Pluto orbits the sun.
- 3: Must have enough mass to be round.
- 4: Pluto is round.
- 5: Must have cleared its orbit of other objects.
- 6: Pluto does not have clear orbit.
Listen again:
M1: Some of you may have heard that astronomers recently agreed that we now have one less planet in our solar system. There are now only eight planets in the solar system. Pluto is no longer considered a planet. Does anyone know why?
W: I think it's because the astronomers changed the requirements for planethood. There's now a stricter definition of a planet.
M2: Yeah, so Pluto no longer qualifies as an actual planet. It's now known as a "dwarf" planet.
M1: That's right, There are now new categories for space objects, but I don't want us to get ahead of ourselves —not just yet. I'd like to take a look at the change in requirements you mentioned and why Pluto no longer qualifies as a planet. Um, there are three requirements that define a planet according to the new standards. Can you think what these might be?
M2: Well, I'd imagine that it would be a space object that orbits around the sun.
M1: Yes, the first requirement is that it is an object in space that orbits the sun. Additionally, that object must have enough mass so that it forms a round shape. See, most smaller objects, like asteroids, do not possess enough mass to pull in other objects around them and overcome their irregular shapes.
M2: Interesting.
M1: The third requirement is that a planet must have cleared the area around its orbit of other objects. There are billions of space objects in our solar system. To be considered a planet, an object must have an unobstructed orbit, free from other objects nearby.
W: Uh, but doesn't Pluto orbit the sun?
M2: And I'm pretty sure it's big enough to be round.
M1: It does orbit the sun, and it is round. However, the problem is that Pluto has an irregular orbit. It changes at times, And because of this, it has not pulled enough smaller surrounding objects into its mass to have an unobstructed orbit. In fact, Pluto's orbit is erratic. Sometimes, it overlaps with the regular and circular orbit of the planet Neptune. So because of this erratic and obstructed orbit, Pluto was disqualified from being a planet under the new, stricter requirements.
