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第一段
1 .Listen to part of a lecture in an astronomy class.
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第二段
1 .OK. We've been discussing the planets in our solar system and how some of the ones farthest from the sun were discovered.
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2 .Well, today I'd like to turn to what are called exoplanets and how researchers detect them. Maria?
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第三段
1 .Exoplanets are planets that orbit around a star other than our Sun, right?
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2 .They are not in our solar system.
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第四段
1 .Right. They have different...what are called "host stars".
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2 .And the study of exoplanets has been getting more and more exciting. Hundreds of them have been discovered so far.
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3 .This is quite remarkable in view of the fact that the discovery of the first exoplanets was confirmed only in the mid-1990s.
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4 .Now we're finding new ones every few weeks or so.
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第五段
1 .So, uh, exactly why are we interested in these exoplanets anyway?
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2 .Is it to see if there's life on them?
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3 .Cuz it seem to me like the only exoplanets we ever hear about are gas giants like Jupiter and Saturn that couldn't possibly support carbon-based life.
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第六段
1 .OK. Well, let's talk about that.
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第七段
1 .First, as for discovering life.
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2 .Well, I think that sort of discovery is pretty far in the future, but it is an eventual goal.
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第八段
1 .For now, the focus is on locating planets within a host star's so called "habitable zone", a zone that's a certain distance from its star because only planets within this zone could conceivably support carbon-based life.
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第九段
1 .So, what would such a planet need?
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第十段
1 .Water?
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第十一段
1 .Yes, it need to be the right temperature to sustain liquid water.
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第十二段
1 .And it would need to be a rocky planet, I mean, as opposed to a gas giant.
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第十三段
1 .OK, good. An Earth-like planet.
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第十四段
1 .Now, as to that, there are some recently detected exoplanets that might actually be Earth-like.
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第十五段
1 .For example, there's a red dwarf star, that's what most stars are, um... that's called Gliese 581.
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第十六段
1 .Gliese 581 is... well, it's a lot more interesting than that name makes it seem.
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2 .This host star is considered a near neighbor of our solar system because it's only about 20 light years away.
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3 .It's pretty close by astronomical standards.
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4 .And being a red dwarf star, it's small and relatively cool, at least compared with the Sun.
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第十七段
1 .And researchers have discovered planets orbiting Gliese 581.
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2 .These exoplanets have been named, ready? Gliese 581 b, c, d, e, in alphabetical order of their discovery.
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第十八段
1 .Gliese 581 d and e are the planets I wanna focus on now.
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2 .See, in 2009, a group of researchers made an announcement.
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3 .These two exoplanets: Gliese 581 d and e do have some Earth-like qualities.
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4 .Gliese 581 d had actually been discovered a couple of years earlier.
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5 .And when its orbit was originally calculated it was thought to be too far away from its host star to be warm enough to support a liquid ocean, let alone carbon-based life.
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6 .But then its orbit was recalculated and now we see that Gliese 581 d is within its host's habitable zone.
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第一十九段
1 .So it might have an ocean?
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第二十段
1 .Well, conceivably.
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第二十一段
1 .See, Gliese 581 d weighs 7 times what Earth weighs and it's unlikely that it's made entirely of rocks because it's so massive.
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2 .The researchers studying it said that it could have a rocky core, an ice layer, a large deep ocean and an atmosphere.
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第二十二段
1 .OK, and there was another announcement along with the recalculated orbit of Gliese 581 d.
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2 .That was the discovery of another planet in the system, Gliese 581 e.
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3 .Compared with other exoplanets, its mass is quite small, only about twice that of Earth.
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第二十三段
1 .So is Gliese 581 e a more Earth-like planet?
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第二十四段
1 .Well, we have to consider its orbit.
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2 .Gliese 581 e orbits its host star in a much shorter period of time than the other planets in the system, meaning it's very close to the star, and therefore too hot for water, for an ocean.
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第二十五段
1 .However, the fact that it's relatively close to the size of Earth, small, in astronomical terms, that was pretty exciting.
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2 .It's impressive that we have the technology to detect it and it bodes well for future research.
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3 .Who knows what we'll find the more we search.
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