新GRE高频阅读机经原文：慧星演变说

　　慧星演变说，pristine relics
　　The long-held perspective that comets are pristine remnants（残留部分） from the formation of the solar system has evolved（演变发展） from the prevailing views of 30 years ago, finds planetary scientist Dr. S. Alan Stern in a paper published in the journal Nature.
　　行星学家Stern博士发现（在Nature上的一篇paper中）：长久以来的一种观点“彗星是太阳系形成时的原始残留物”是30年前一种流行观点的演化。
　　"It's fair to say that a sea change has taken place," says Stern, director of the Space Studies Department in the SwRI Space Science and Engineering Division. "We used to consider comets as wholly unchanged relics that had been stored ever since the era of solar system formation in a distant, cold, timeless deep freeze called the Oort cloud. We now appreciate that a variety of processes slowly modify comets during their storage there," he says. "As a result, it's become clear that the Oort cloud and its cousin the Kuiper Belt are not such perfect deep freezes."
　　我们过去认为彗星是从太阳系建立时起就存储在一个distant, cold, timeless deep freeze的叫做Oort cloud中不变的残余物。我们现在认为存储时许多缓慢的过程改变了彗星，所以很明显Oort cloud和Kuiper Belt不是完美的deep freezes。
　　The first evolutionary process to be recognized as affecting comets during their long storage was radiation damage, followed by the discovery that sandblasting from dust grains in the interstellar medium plays an important role. Next, researchers theorized that comets in the Oort cloud are heated to scientifically significant temperatures by passing stars and supernovae, says Stern. More recently, researchers are finding that comets in the Kuiper Belt are heavily damaged by collisions.
　　第一个进化过程：放射损坏，在一个发现。。。之后。然后，研究者认为Oort cloud中的彗星在经过stars and supernovae时被加热。最近，研究者发现Kuiper Belt里的彗星损毁严重。
　　"It also now seems inevitable that most comets from the Kuiper Belt, though constructed of ancient material, cannot themselves be ancient -- instead they must be 'recently' created chips off larger Kuiper Belt Objects, formed as a result of violent impacts," says Stern. "This is truly a paradigm shift. Many of the short-period comets we see aren't even ancient!"
　　我们看见的彗星其实已经被损坏了，不是ancient。
　　The classical view that comets do not evolve while they are stored far from the sun in the Oort cloud and Kuiper Belt began to change as far back as the 1970s, but the pace of discoveries about the way comets evolve picked up considerably in the 1980s and 1990s.
　　不变的观点可以追溯到1970s，发现彗星演变的步伐加速发生在1980 s and 1990s
　　As a result of these findings, astronomers now better appreciate that comets, though still the most pristine bodies known, have been modified in several important ways since their birth, says Stern.
　　作为上述发现的结果，天文学家现在认为彗星虽然还是已知的最原始的东西，但的确从诞生开始在某些重要的方面发生了改变。
　　The realization that comets evolve during their long storage in the Oort cloud and Kuiper Belt provides insight and context to more confidently evaluate the results of astronomical and space mission observations of comets. So, too, it suggests that cometary sample return missions now on the drawing board for NASA should employ relatively deep subsurface sampling if truly pristine, ancient material is to be collected.
　　意识到彗星演变 给更可信的评估彗星观测结果 提供了远见和背景。它也表明如果收集到更原始的彗星样本，应该用相对深的表面的样本。