GRE阅读高频机经原文：彗星的pristine relics
<p> 11. 彗星的<span word="pristine">pristine</span> <span word="relics">relics</span></p><p> <span word="The">The</span> <span word="long">long</span>-<span word="held">held</span> <span word="perspective">perspective</span> <span word="that">that</span> <span word="comets">comets</span> <span word="are">are</span> <span word="pristine">pristine</span> <span word="remnants">remnants</span> <span word="from">from</span> <span word="the">the</span> <span word="formation">formation</span> <span word="of">of</span> <span word="the">the</span> <span word="solar">solar</span> <span word="system">system</span> <span word="has">has</span> <span word="evolved">evolved</span> <span word="from">from</span> <span word="the">the</span> <span word="prevailing">prevailing</span> <span word="views">views</span> <span word="of">of</span> 30 <span word="years">years</span> <span word="ago">ago</span>, <span word="finds">finds</span> <span word="planetary">planetary</span> <span word="scientist">scientist</span> <span word="Dr">Dr</span>. <span word="S">S</span>. <span word="Alan">Alan</span> <span word="Stern">Stern</span> <span word="in">in</span> <span word="a">a</span> <span word="paper">paper</span> <span word="published">published</span> <span word="in">in</span> <span word="the">the</span> <span word="journal">journal</span> <span word="Nature">Nature</span>.</p><p> <span word="Its">Its</span> <span word="fair">fair</span> <span word="to">to</span> <span word="say">say</span> <span word="that">that</span> <span word="a">a</span> <span word="sea">sea</span> <span word="change">change</span> <span word="has">has</span> <span word="taken">taken</span> <span word="place">place</span>, <span word="says">says</span> <span word="Stern">Stern</span>, <span word="director">director</span> <span word="of">of</span> <span word="the">the</span> <span word="Space">Space</span> <span word="Studies">Studies</span> <span word="Department">Department</span> <span word="in">in</span> <span word="the">the</span> <span word="SwRI">SwRI</span> <span word="Space">Space</span> <span word="Science">Science</span> <span word="and">and</span> <span word="Engineering">Engineering</span> <span word="Division">Division</span>. <span word="We">We</span> <span word="used">used</span> <span word="to">to</span> <span word="consider">consider</span> <span word="comets">comets</span> <span word="as">as</span> <span word="wholly">wholly</span> <span word="unchanged">unchanged</span> <span word="relics">relics</span> <span word="that">that</span> <span word="had">had</span> <span word="been">been</span> <span word="stored">stored</span> <span word="ever">ever</span> <span word="since">since</span> <span word="the">the</span> <span word="era">era</span> <span word="of">of</span> <span word="solar">solar</span> <span word="system">system</span> <span word="formation">formation</span> <span word="in">in</span> <span word="a">a</span> <span word="distant">distant</span>, <span word="cold">cold</span>, <span word="timeless">timeless</span> <span word="deep">deep</span> <span word="freeze">freeze</span> <span word="called">called</span> <span word="the">the</span> <span word="Oort">Oort</span> <span word="cloud">cloud</span>. <span word="We">We</span> <span word="now">now</span> <span word="appreciate">appreciate</span> <span word="that">that</span> <span word="a">a</span> <span word="variety">variety</span> <span word="of">of</span> <span word="processes">processes</span> <span word="slowly">slowly</span> <span word="modify">modify</span> <span word="comets">comets</span> <span word="during">during</span> <span word="their">their</span> <span word="storage">storage</span> <span word="there">there</span>, <span word="he">he</span> <span word="says">says</span>. <span word="As">As</span> <span word="a">a</span> <span word="result">result</span>, <span word="its">its</span> <span word="become">become</span> <span word="clear">clear</span> <span word="that">that</span> <span word="the">the</span> <span word="Oort">Oort</span> <span word="cloud">cloud</span> <span word="and">and</span> <span word="its">its</span> <span word="cousin">cousin</span> <span word="the">the</span> <span word="Kuiper">Kuiper</span> <span word="Belt">Belt</span> <span word="are">are</span> <span word="not">not</span> <span word="such">such</span> <span word="perfect">perfect</span> <span word="deep">deep</span> <span word="freezes">freezes</span>.</p><p> <span word="The">The</span> <span word="first">first</span> <span word="evolutionary">evolutionary</span> <span word="process">process</span> <span word="to">to</span> <span word="be">be</span> <span word="recognized">recognized</span> <span word="as">as</span> <span word="affecting">affecting</span> <span word="comets">comets</span> <span word="during">during</span> <span word="their">their</span> <span word="long">long</span> <span word="storage">storage</span> <span word="was">was</span> <span word="radiation">radiation</span> <span word="damage">damage</span>, <span word="followed">followed</span> <span word="by">by</span> <span word="the">the</span> <span word="discovery">discovery</span> <span word="that">that</span> <span word="sandblasting">sandblasting</span> <span word="from">from</span> <span word="dust">dust</span> <span word="grains">grains</span> <span word="in">in</span> <span word="the">the</span> <span word="interstellar">interstellar</span> <span word="medium">medium</span> <span word="plays">plays</span> <span word="an">an</span> <span word="important">important</span> <span word="role">role</span>. <span word="Next">Next</span>, <span word="researchers">researchers</span> <span word="theorized">theorized</span> <span word="that">that</span> <span word="comets">comets</span> <span word="in">in</span> <span word="the">the</span> <span word="Oort">Oort</span> <span word="cloud">cloud</span> <span word="are">are</span> <span word="heated">heated</span> <span word="to">to</span> <span word="scientifically">scientifically</span> <span word="significant">significant</span> <span word="temperatures">temperatures</span> <span word="by">by</span> <span word="passing">passing</span> <span word="stars">stars</span> <span word="and">and</span> <span word="supernovae">supernovae</span>, <span word="says">says</span> <span word="Stern">Stern</span>. <span word="More">More</span> <span word="recently">recently</span>, <span word="researchers">researchers</span> <span word="are">are</span> <span word="finding">finding</span> <span word="that">that</span> <span word="comets">comets</span> <span word="in">in</span> <span word="the">the</span> <span word="Kuiper">Kuiper</span> <span word="Belt">Belt</span> <span word="are">are</span> <span word="heavily">heavily</span> <span word="damaged">damaged</span> <span word="by">by</span> <span word="collisions">collisions</span>.</p><p> <span word="It">It</span> <span word="also">also</span> <span word="now">now</span> <span word="seems">seems</span> <span word="inevitable">inevitable</span> <span word="that">that</span> <span word="most">most</span> <span word="comets">comets</span> <span word="from">from</span> <span word="the">the</span> <span word="Kuiper">Kuiper</span> <span word="Belt">Belt</span>, <span word="though">though</span> <span word="constructed">constructed</span> <span word="of">of</span> <span word="ancient">ancient</span> <span word="material">material</span>, <span word="cannot">cannot</span> <span word="themselves">themselves</span> <span word="be">be</span> <span word="ancient">ancient</span> -- <span word="instead">instead</span> <span word="they">they</span> <span word="must">must</span> <span word="be">be</span> <span word="recently">recently</span> <span word="created">created</span> <span word="chips">chips</span> <span word="off">off</span> <span word="larger">larger</span> <span word="Kuiper">Kuiper</span> <span word="Belt">Belt</span> <span word="Objects">Objects</span>, <span word="formed">formed</span> <span word="as">as</span> <span word="a">a</span> <span word="result">result</span> <span word="of">of</span> <span word="violent">violent</span> <span word="impacts">impacts</span>, <span word="says">says</span> <span word="Stern">Stern</span>. <span word="This">This</span> <span word="is">is</span> <span word="truly">truly</span> <span word="a">a</span> <span word="paradigm">paradigm</span> <span word="shift">shift</span>. <span word="Many">Many</span> <span word="of">of</span> <span word="the">the</span> <span word="short">short</span>-<span word="period">period</span> <span word="comets">comets</span> <span word="we">we</span> <span word="see">see</span> <span word="arent">arent</span> <span word="even">even</span> <span word="ancient">ancient</span>!</p>
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