一

个新客人及时赶赴感恩节晚餐，但显然没在节日活动中活下来。

这位访客是一颗名叫伊森(ISON)的原始彗星，自走出家门已至少有100万年，它于美东时间周四下午飞抵近日点。

然而根据多个航天器发回的照片，科学家似乎一致认为，伊森同神话人物伊卡洛斯(Icarus)一般，已在与太阳的近距离接触中"死去"。

NASA

2013年11月25日，美国国家航空航天局的一个飞行器拍摄到了彗星伊森。当时伊森正向太阳移动。

此前，全世界上千位天文学家翘首期盼着彗星扫过太阳的那一刻，并且在其"生还"希望变得渺茫前，科学家曾预测伊森或将环绕太阳并在北半球上空散发出肉眼可见的明亮光芒。

而现在科学家怀疑它已破碎成无数个碎片，再也无法见到。

科罗拉多州博尔德太空科学研究所(Space Science Institute)的行星科学家费希尔(Padma Yanamandra-Fisher)在彗星接近太阳之前说，观察显示，这颗彗星在靠近太阳前曾一度变亮又失去了亮度。因而许多人猜测它或许正在消亡。

自一年多前被发现以来，伊森的运行状态就不断地令天文学家感到惊讶，而他们一直期望这颗彗星仍能展现出美丽的奇观。比如周一这颗彗星看起来似乎将解体，然而周二它依然存在着。

除了是个天体淘气鬼，伊森还成为了有史以来追踪者最多的彗星之一。

上千台业余、专业和太空望远镜都被瞄准这颗原始彗星。该彗星体型较小，由石块和冰组成，直径不超过五、六公里。

2012年9月，俄罗斯天文学家涅夫斯基(Vitali Nevski)和诺维切诺克(Artyom Novichonok)利用国际科学光学观测网(International Scientific Optical Network, ISON)的数据发现了这颗彗星，并以观测网的英文缩写命名了这颗彗星。

现世从未见过像伊森这样的彗星。它是一颗罕见的掠日彗星，其飞行轨道与太阳极其贴近。

不同于像著名的哈雷彗星(Halley)这样的频繁来往的周期彗星，伊森是一颗原始彗星，而这是它第一次飞向太阳，其组成（主要为岩石和冰）自约450万年前彗星形成以来几乎没有变化，这使得它成为太阳系里最古老的天体之一。

令科学家感兴趣的原因不仅是伊森离太阳之近，还因其成份研究能够为太阳系起源提供有价值的线索。

当一颗新的彗星飞近太阳时，极大的热量会将构成这颗彗星的稀有材质暴露出来，例如金属。

亚利桑那州洛厄尔天文台(Lowell Observatory)的奈特(Matthew Knight)说，这是200年来我们所看到的第一颗崭新的掠日彗星。

如果伊森没有解体，科学家预测它将会在12月的第一周展现光芒，至少北半球的人们将能看到它。

奈特在周四彗星"致命"的近日之旅前说，它将在接近日出时从地平线升起，并拖着一条很长很明亮的彗尾。

他说，如果你在（日出）30分钟前来到户外，你应该就能用肉眼看到它。

不过前提是伊森能在周四飞过太阳时"存活"下来。

A new guest arrived just in time for Thanksgiving dinner, but apparently didn't survive the festivities.

The visitor, a pristine comet called ISON that left its home at least a million years ago, made its closest approach to the sun Thursday afternoon.

But based on images arriving from various spacecraft, the consensus among scientists appeared to be that ISON, like the mythical Icarus, didn't survive its close encounter with the sun.

The comet's sweep near the sun was a moment that thousands of astronomers around the world had anxiously awaited, and before hopes dimmed about its survival, ISON was predicted to possibly loop around the star and emerge as a bright object visible to the naked eye in the skies of the Northern Hemisphere.

However, scientists now suspect it fragmented into countless pieces-never to be seen again.

Before the close approach, observations 'showed that the comet had brightened and then lost brightness. So there's a lot of conjecture that it might be fading,' said Padma Yanamandra-Fisher, a planetary scientist at the Space Science Institute in Boulder, Colo., before the comet made its close pass with the sun.

Since it was spotted more than a year ago, ISON's behavior has constantly surprised astronomers, and they had held out hope that the comet could still put on a pretty display. On Monday, for example, it looked like it wouldn't survive. Yet it was still there on Tuesday.

In addition to being a cosmic tease, ISON was one of the most tracked comets in history.

Thousands of telescopes-amateur, professional and space-borne-were being trained on this relatively tiny clump of ancient rock and ice no more than three or four miles in diameter.

The comet was discovered in September 2012 by Russian astronomers Vitali Nevski and Artyom Novichonok using data from the International Scientific Optical Network, whose initials provided the name.

Nothing like ISON has been seen in living memory. It is a relatively rare 'sungrazer,' a comet that flies especially close to our sun.

Unlike periodic comets that come and go like the famous Halley's, ISON is pristine and was making its first journey toward the sun. Its composition-mainly rock and ice-has barely changed since it formed some 4.5 billion years ago, making it one of the oldest objects in the solar system.

That had scientists intrigued, because ISON's proximity to the sun, and the chance to study what it is made of, could provide valuable clues about origins of the solar system.

When a new comet flies close to the sun, the tremendous heat can help reveal rarer materials, such as metals, of which it is made.

'It's the first time in 200 years that we've seen a comet that's both a sungrazer and brand new,' said Matthew Knight from the Lowell Observatory in Arizona.

If ISON had survived, scientists predicted it would have been poised to put on a display in the first week of December, at least for Northern Hemisphere viewers.

'It would have a very long and bright tail as it comes up from the horizonshortly before sunrise,' said Dr. Knight, before Thursday's fatal close encounter.

'If you go out 30 minutes before [sunrise], you should be able to see it with the naked eye.'

But that was only if ISON had survived Thursday's flyby.

• scientific [,saiən´tifik]   a.科学(上)的   (初中英语单词)
• survive [sə´vaiv]   vt.幸存；残存   (初中英语单词)
• visitor [´vizitə]   n.访问者；来宾；参观者   (初中英语单词)
• encounter [in´kauntə]   vt.&n.偶然相遇；冲突   (初中英语单词)
• emerge [i´mə:dʒ]   vi.出现；显露；暴露   (初中英语单词)
• visible [´vizəbəl]   a.可见的；明显的   (初中英语单词)
• suspect [´sʌspekt, sə´spekt]   v.怀疑；觉得 n.嫌疑犯   (初中英语单词)
• institute [´institju:t]   n.学院 vt.建立；设置   (初中英语单词)
• constantly [´kɔnstəntli]   ad.经常地；不断地   (初中英语单词)
• addition [ə´diʃən]   n.加；加法；附加物   (初中英语单词)
• professional [prə´feʃənəl]   a.职业的 n.自由职业   (初中英语单词)
• international [,intə´næʃənəl]   a.国际的，世界的   (初中英语单词)
• barely [´beəli]   ad.公开地；仅仅   (初中英语单词)
• valuable [´væljuəbəl, -jubəl]   a.有价值的，贵重的   (初中英语单词)
• tremendous [tri´mendəs]   a.可怕的；巨大的   (初中英语单词)
• horizon [hə´raizən]   n.地平线；范围；视野   (初中英语单词)
• shortly [´ʃɔ:tli]   ad.立刻，马上；不久   (初中英语单词)
• thanksgiving [´θæŋks,giviŋ]   感恩节   (高中英语单词)
• apparently [ə´pærəntli]   ad.显然，表面上地   (高中英语单词)
• anxiously [´æŋkʃəsli]   ad.挂念地；渴望地   (高中英语单词)
• countless [´kauntlis]   a.无数的   (高中英语单词)
• brightness [´braitnis]   n.光明；快乐   (高中英语单词)
• scientist [´saiəntist]   n.(自然)科学家   (高中英语单词)
• behavior [bi´heiviə]   n.举止，行为   (高中英语单词)
• relatively [´relətivli]   ad.比较地；相对地   (高中英语单词)
• billion [´biljən]   num.万亿   (高中英语单词)
• knight [nait]   n.骑士；爵士   (高中英语单词)
• network [´netwə:k]   n.网状物 vt.联播   (英语四级单词)
• conjecture [kən´dʒektʃə]   n.&v.猜测(想)；设想   (英语四级单词)
• boulder [´bəuldə]   n.大石头，卵石；巨砾   (英语四级单词)
• hemisphere [´hemisfiə]   n.半球；范围，领域   (英语四级单词)
• observatory [əb´zə:vətəri]   n.天文台；气象台   (英语六级单词)