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科學新發現／隕石對撞 恐龍滅絕遠因
更新日期:
2007/09/07 04:09
〔編譯陳成良／綜合報導〕六千五百萬年前，一顆寬十公里的隕石撞擊現今墨西哥猶加敦半島，據信導致恐龍滅絕。五日公佈的一項研究報告指出，恐龍覆亡的命運，其實早在兩塊大隕石於恐龍從地球上消失之前約一億年發生對撞時，就已注定。
一億六千萬年前 宇宙驚天爆
這項發表於最新一期「自然」期刊的研究，試圖解釋過去一、兩億年間，為何地球與月球隕石坑形成的速率顯然增加一倍。美國西 南研究院伯特基教授領導的研究小組，追蹤到約一億六千五百萬年前一場隕石撞擊事件。他們所作的電腦模擬資料及化學分析顯示，當時一顆直徑一七○公里的大隕 石，遭一顆直徑六十公里的較小隕石以每秒三公里的速度撞擊，而裂解為成千上萬個小流星，形成現在我們所知的「Baptistina流星家族」。
碎片撞擊地球、金星、火星表面
解 體後產生的隕石碎片，不斷撞擊地球、月球、金星及火星表面，留下的「傷痕」至今可見。其中一塊體積較大的碎片，在太空中盤旋九千五百萬年後，撞擊地球，造 成距今六千五百萬年前的白堊紀─第三紀物種大滅絕事件，並在猶加敦半島形成一個稱為Chicxulub的隕石坑，導致恐龍滅絕。
近地天體 三分之一來自Baptistina
Baptistina流星雨持 續對地球構成威脅，它產生的小隕石中，至少一千顆直徑都在一公里以上。據統計，目前運行軌道與地球軌道相交的「近地天體」中，有五分之一至三分之一都屬於 Baptistina流星家族。不過，這些近地天體與地球相撞的機率極低，地球遭直徑十公里的外太空物體撞擊，更是平均三億五千萬年才會發生一次。
Asteroid impacts
小行星撞擊
Baptistina's terrible daughters
Baptistina的「恐怖女兒」
Astronomers have traced the asteroid that killed the dinosaurs
天文學家追蹤到曾經殺死恐龍的小行星
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IT WAS once suggested, to illustrate the chaotic and unpredictable way in which natural systems behave, that the beat of a butterfly's wing in China could eventually trigger a hurricane in the Atlantic. A bit of an exaggeration, perhaps, but the point was that even in the theoretically deterministic world of Newtonian mechanics, only a small amount of complexity is needed to make practical prediction well nigh impossible.
為說明自然規律的混亂無序和不可預知，曾有這樣的說法：中國的一隻蝴蝶拍打一下翅膀最終可能會引起大西洋的一場颶風。這也許有點誇張，但關鍵是即使在牛頓力學的理論決定學界，僅僅是少量的複雜因素也會給實際預測帶來不確定性。
Thus it is perhaps not as far-fetched as it sounds to suggest that the collision 160m years ago of two space rocks, albeit quite large ones, resulted in the stormy death almost 100m years later of the dinosaurs and many other species on Earth. For although the orbits of the planets look to astronomers like a model of regular, Newtonian clockwork, on a scale of millions of years, the solar system is every bit as chaotic as the Earth's weather.
因此，一億六千萬年前兩顆宇宙隕石的碰撞，雖然其巨大無比，但卻導致了一億年前地球上恐龍與其它物種的死亡，這種說法聽起來也許並不顯牽強。(因此，以下說法聽起來也許並不顯牽強，即一億六千萬年前兩顆宇宙隕石的碰撞，雖然其巨大無比，但卻導致了一億年前地球上恐龍與其它物種的死亡。/因此，1億6千萬年前的兩塊宇宙隕石的碰撞，雖是巨型石塊，導致1億年後地球上恐龍和其它物種的急風暴雨式的死亡的說法也不顯牽強)。因為對天文學家來說，儘管行星的軌道有如牛頓的有規律發條裝置模型，在數百萬年的範圍內，太陽系像地球上的天氣一樣混亂無序。
That such a collision was, indeed, responsible for the demise of the dinosaurs is a suggestion made in the September 6th issue of Nature by William Bottke and his colleagues at the Southwest Research Institute in Boulder, Colorado. Dr Bottke has been tracking the orbits of asteroids. These rocky minor planets, most of which are located between the orbits of Mars and Jupiter, often come in families. Members share both chemical composition (which can be deduced from the spectrum of the light they reflect) and orbital characteristics. The assumption is that such families are the daughters of single, larger bodies that have been hit by other asteroids and smashed into pieces. Dr Bottke thinks he has traced one such family back to its original collision.
「這樣的撞擊確實造成了恐龍的滅亡」，科羅拉多州玻爾得的西南研究所的William Bottke和他的同事們在 9月6日那期的《自然》雜誌上如是說。Bottke博士一直在追蹤小行星的運行軌跡。這些隕石小行星大部分在火星和木星的軌道間，且大都以「家族成員」的形式出現。研究人員借助其化學成分（可由光反射譜推得）和軌道特徵的資料，得出這樣的結論：這些「家族成員」是單親的「女兒」，大行星被其它小行星撞碎為數塊。Bottke博士說他已從其中一顆小行星追溯到最早的撞擊。
A smashing time
撞擊時代
The largest member of the family in question is called Baptistina, and is some 40km (25 miles) across. In addition to her, the team identified many more than 2,000 smaller objects as belonging to the same family. They were able to do this by looking at those asteroids' orbits in detail.
其中最大的家庭成員叫Baptistina，跨度達40公里（25英里）。除此之外，研究小組發現多於2,000個較小的屬於同一家族的小行星，他們是從詳細研究小行星的軌道得知的。
One of the chaotic things that happen to the paths taken by asteroids is caused by sunlight, and is known as the Yarkovsky effect. Just as most orbiting planets spin on their axes, so asteroids also rotate. When part of an asteroid's surface passes from night to day, it starts to warm up. Because of thermal inertia, the time at which it reaches its maximum temperature comes somewhat after local 「noon」, a phenomenon that any sunbather will recognise. Since the heat it radiates back into space depends on its temperature, the afternoon side of an asteroid radiates more heat than the morning side. The reaction to this radiation is greater on the afternoon side than on the morning side and there is thus a small force pushing on the afternoon side that gradually distorts the asteroid's orbit. The smaller the asteroid in question, the faster that distortion happens.
小行星的軌道混亂無序的原因之一是由光照引起，被稱作雅科夫斯基效應（Yarkovsky effect）。 正如其它沿軌道運行的行星自轉一樣，這些小行星也有自轉。當一個小行星的部分表面由黑夜轉入天明時開始轉暖。由於熱慣性，當溫度達到最高時常在「正午」偏 後，日光浴者深知這一現象。正因為輻射回宇宙的熱量取決於其溫度的高低，所以，小行星的下午會比上午輻射更多的熱量。下午的熱輻射反作用力就大於上午，因 此，始終有那麼點力作用於下午一側，逐漸地就使小行星偏離軌道。小行星越小，偏離軌道就越快。
The result is that the daughters of Baptistina have become scattered farther and farther away from their mother. From the pattern of this scattering, and from the sizes of the asteroids (which tells you how fast they will scatter), it is possible to calculate the date of the original collision. That turns out to be 160m years ago, give or take about 20m years.
這樣的結果就是，Baptistina的女兒們分散得離她們的母親愈來愈遠。通過模擬這種分散和小行星的大小（可以得出分散的速度）可以計算出最初的碰撞年代，結果是1億6千萬年前，大約有2千萬年的誤差。
That the dinosaurs were killed off 65m years ago by an asteroid impact is now widely accepted. Dr Bottke's contention is that the deed was done by one of Baptistina's daughters. His evidence is twofold. First, the surviving debris from the devastating impact has the same composition as Baptistina and her offspring. That is a necessary but not a sufficient condition, as the type of rock involved, called carbonaceous chondrite, is found in other asteroids, too. The second line of evidence is the 「case of the missing daughters」.
6千5百萬年前，小行星的撞擊導致恐龍的滅亡的說法已被廣泛接受。Bottke博士的觀點是，這一事實是Baptistina的女兒所為。他有兩方面的證據：第一，現存的災難性撞擊的殘骸與Baptistina和她的後代有相同的成分，這是必要條件，但並非充分條件，因為含碳的球粒狀隕石在其它小行星上也有；第二，「失蹤女兒的事實」。
The cluster of Baptistina's young has a gap in it. This corresponds to a place where the gravitational pulls of Mars and Jupiter have conspired to change the orbits of any asteroids much faster than the Yarkovsky effect could manage alone. Such asteroids would rapidly have adopted orbits that cut across those of the inner planets, including Earth. Many of the larger ones would have started arriving about 100m years ago. Sooner or later, collisions would have been inevitable.
Baptistina的後代各不相同。與此相一致的是，在火星和木星共同的引力作用下改變小行星的軌道要比單一的雅科夫斯基效應（Yarkovsky effect）改變其軌道要快得多。這些小行星在橫越其它內部行星後就會快速改變軌道，其中也包括地球。有些較大的可能在1億年前出現。碰撞遲早是不可避免的。
Those collisions are why the asteroids that ought to be in the space are missing. They are probably also the explanation for the fact that, over the past 100m years or so, the number of asteroids that have hit the Earth is about twice that which would have been expected. Taking into account the circumstances that pertained 65m years ago, Dr Bottke reckons it more than 90% probable that the dinosaur killer was one of Baptistina's daughters.
那些撞擊就解釋了為什麼宇宙中小行星會失蹤。也許還可能解釋這樣的事實，那就是在過去大約1億年間，撞擊地球的小行星的數量是原來預計的兩倍。再加上6千5百萬年前的環境因素，Bottke博士估計，恐龍殺手有90%以上的可能是Baptistina之女。
The hole made by that collision, in what is now the Yucatan Peninsula in southern Mexico, has long since been buried in thick layers of sediment under the sea. But anyone with a pair of field glasses can see for himself what Baptistina's daughters are capable of.
當今墨西哥南部的尤卡坦半島中有當年撞擊形成的洞，現早就被海底厚層沉澱物所掩埋。但每位配戴野外雙筒望遠鏡的人都可以領略到Baptistina之女的能力。
The lunar crater named after Tycho Brahe, a 16th century Danish astronomer, near the moon's south pole, is 85km across. It is surrounded by rays of ejecta that stretch across much of the southern lunar hemisphere, indicating the violence of the impact that formed it. It is thought to be just over 100m years old (Apollo 17 brought back material from the site, which allowed it to be dated), and it is reckoned by Dr Bottke to be the result of the moon encountering one of the first of Baptistina's progeny to arrive in the inner solar system. It is a beautiful sight. But you would not have wanted to witness, at close quarters, its creation.
第谷•佈雷赫是16世紀的丹麥天文學家，月球表面的那座環形山就是以他的名字命名。此山在靠近月球的南極，跨度達85公里。周圍是覆蓋南半球的連綿的火山噴出物，這表明在形成此山時的撞擊有多麼劇烈。據估計，此山剛有1億年的歷史（阿波羅17號曾帶回其地質樣品，並以此計算出年代），Bottke說，這是在月球偶遇Baptistina的第一個進入太陽系內部的後代時產生的結果。此景甚是壯觀，但估計你並不想實地見證其形成過程。
天文學家追蹤到曾經殺死恐龍的小行星
IT WAS once suggested, to illustrate the chaotic and unpredictable way in which natural systems behave, that the beat of a butterfly's wing in China could eventually trigger a hurricane in the Atlantic. A bit of an exaggeration, perhaps, but the point was that even in the theoretically deterministic world of Newtonian mechanics, only a small amount of complexity is needed to make practical prediction well nigh impossible.
為說明自然規律的混亂無序和不可預知，曾有這樣的說法：中國的一隻蝴蝶拍打一下翅膀最終可能會引起大西洋的一場颶風。這也許有點誇張，但關鍵是即使在牛頓力學的理論決定學界，僅僅是少量的複雜因素也會給實際預測帶來不確定性。
Thus it is perhaps not as far-fetched as it sounds to suggest that the collision 160m years ago of two space rocks, albeit quite large ones, resulted in the stormy death almost 100m years later of the dinosaurs and many other species on Earth. For although the orbits of the planets look to astronomers like a model of regular, Newtonian clockwork, on a scale of millions of years, the solar system is every bit as chaotic as the Earth's weather.
因此，一億六千萬年前兩顆宇宙隕石的碰撞，雖然其巨大無比，但卻導致了一億年前地球上恐龍與其它物種的死亡，這種說法聽起來也許並不顯牽強。(因此，以下說法聽起來也許並不顯牽強，即一億六千萬年前兩顆宇宙隕石的碰撞，雖然其巨大無比，但卻導致了一億年前地球上恐龍與其它物種的死亡。/因此，1億6千萬年前的兩塊宇宙隕石的碰撞，雖是巨型石塊，導致1億年後地球上恐龍和其它物種的急風暴雨式的死亡的說法也不顯牽強)。因為對天文學家來說，儘管行星的軌道有如牛頓的有規律發條裝置模型，在數百萬年的範圍內，太陽系像地球上的天氣一樣混亂無序。
That such a collision was, indeed, responsible for the demise of the dinosaurs is a suggestion made in the September 6th issue of Nature by William Bottke and his colleagues at the Southwest Research Institute in Boulder, Colorado. Dr Bottke has been tracking the orbits of asteroids. These rocky minor planets, most of which are located between the orbits of Mars and Jupiter, often come in families. Members share both chemical composition (which can be deduced from the spectrum of the light they reflect) and orbital characteristics. The assumption is that such families are the daughters of single, larger bodies that have been hit by other asteroids and smashed into pieces. Dr Bottke thinks he has traced one such family back to its original collision.
「這樣的撞擊確實造成了恐龍的滅亡」，科羅拉多州玻爾得的西南研究所的William Bottke和他的同事們在 9月6日那期的《自然》雜誌上如是說。Bottke博士一直在追蹤小行星的運行軌跡。這些隕石小行星大部分在火星和木星的軌道間，且大都以「家族成員」的形式出現。研究人員借助其化學成分（可由光反射譜推得）和軌道特徵的資料，得出這樣的結論：這些「家族成員」是單親的「女兒」，大行星被其它小行星撞碎為數塊。Bottke博士說他已從其中一顆小行星追溯到最早的撞擊。
A smashing time
撞擊時代
The largest member of the family in question is called Baptistina, and is some 40km (25 miles) across. In addition to her, the team identified many more than 2,000 smaller objects as belonging to the same family. They were able to do this by looking at those asteroids' orbits in detail.
其中最大的家庭成員叫Baptistina，跨度達40公里（25英里）。除此之外，研究小組發現多於2,000個較小的屬於同一家族的小行星，他們是從詳細研究小行星的軌道得知的。
One of the chaotic things that happen to the paths taken by asteroids is caused by sunlight, and is known as the Yarkovsky effect. Just as most orbiting planets spin on their axes, so asteroids also rotate. When part of an asteroid's surface passes from night to day, it starts to warm up. Because of thermal inertia, the time at which it reaches its maximum temperature comes somewhat after local 「noon」, a phenomenon that any sunbather will recognise. Since the heat it radiates back into space depends on its temperature, the afternoon side of an asteroid radiates more heat than the morning side. The reaction to this radiation is greater on the afternoon side than on the morning side and there is thus a small force pushing on the afternoon side that gradually distorts the asteroid's orbit. The smaller the asteroid in question, the faster that distortion happens.
小行星的軌道混亂無序的原因之一是由光照引起，被稱作雅科夫斯基效應（Yarkovsky effect）。 正如其它沿軌道運行的行星自轉一樣，這些小行星也有自轉。當一個小行星的部分表面由黑夜轉入天明時開始轉暖。由於熱慣性，當溫度達到最高時常在「正午」偏 後，日光浴者深知這一現象。正因為輻射回宇宙的熱量取決於其溫度的高低，所以，小行星的下午會比上午輻射更多的熱量。下午的熱輻射反作用力就大於上午，因 此，始終有那麼點力作用於下午一側，逐漸地就使小行星偏離軌道。小行星越小，偏離軌道就越快。
The result is that the daughters of Baptistina have become scattered farther and farther away from their mother. From the pattern of this scattering, and from the sizes of the asteroids (which tells you how fast they will scatter), it is possible to calculate the date of the original collision. That turns out to be 160m years ago, give or take about 20m years.
這樣的結果就是，Baptistina的女兒們分散得離她們的母親愈來愈遠。通過模擬這種分散和小行星的大小（可以得出分散的速度）可以計算出最初的碰撞年代，結果是1億6千萬年前，大約有2千萬年的誤差。
That the dinosaurs were killed off 65m years ago by an asteroid impact is now widely accepted. Dr Bottke's contention is that the deed was done by one of Baptistina's daughters. His evidence is twofold. First, the surviving debris from the devastating impact has the same composition as Baptistina and her offspring. That is a necessary but not a sufficient condition, as the type of rock involved, called carbonaceous chondrite, is found in other asteroids, too. The second line of evidence is the 「case of the missing daughters」.
6千5百萬年前，小行星的撞擊導致恐龍的滅亡的說法已被廣泛接受。Bottke博士的觀點是，這一事實是Baptistina的女兒所為。他有兩方面的證據：第一，現存的災難性撞擊的殘骸與Baptistina和她的後代有相同的成分，這是必要條件，但並非充分條件，因為含碳的球粒狀隕石在其它小行星上也有；第二，「失蹤女兒的事實」。
The cluster of Baptistina's young has a gap in it. This corresponds to a place where the gravitational pulls of Mars and Jupiter have conspired to change the orbits of any asteroids much faster than the Yarkovsky effect could manage alone. Such asteroids would rapidly have adopted orbits that cut across those of the inner planets, including Earth. Many of the larger ones would have started arriving about 100m years ago. Sooner or later, collisions would have been inevitable.
Baptistina的後代各不相同。與此相一致的是，在火星和木星共同的引力作用下改變小行星的軌道要比單一的雅科夫斯基效應（Yarkovsky effect）改變其軌道要快得多。這些小行星在橫越其它內部行星後就會快速改變軌道，其中也包括地球。有些較大的可能在1億年前出現。碰撞遲早是不可避免的。
Those collisions are why the asteroids that ought to be in the space are missing. They are probably also the explanation for the fact that, over the past 100m years or so, the number of asteroids that have hit the Earth is about twice that which would have been expected. Taking into account the circumstances that pertained 65m years ago, Dr Bottke reckons it more than 90% probable that the dinosaur killer was one of Baptistina's daughters.
那些撞擊就解釋了為什麼宇宙中小行星會失蹤。也許還可能解釋這樣的事實，那就是在過去大約1億年間，撞擊地球的小行星的數量是原來預計的兩倍。再加上6千5百萬年前的環境因素，Bottke博士估計，恐龍殺手有90%以上的可能是Baptistina之女。
The hole made by that collision, in what is now the Yucatan Peninsula in southern Mexico, has long since been buried in thick layers of sediment under the sea. But anyone with a pair of field glasses can see for himself what Baptistina's daughters are capable of.
當今墨西哥南部的尤卡坦半島中有當年撞擊形成的洞，現早就被海底厚層沉澱物所掩埋。但每位配戴野外雙筒望遠鏡的人都可以領略到Baptistina之女的能力。
The lunar crater named after Tycho Brahe, a 16th century Danish astronomer, near the moon's south pole, is 85km across. It is surrounded by rays of ejecta that stretch across much of the southern lunar hemisphere, indicating the violence of the impact that formed it. It is thought to be just over 100m years old (Apollo 17 brought back material from the site, which allowed it to be dated), and it is reckoned by Dr Bottke to be the result of the moon encountering one of the first of Baptistina's progeny to arrive in the inner solar system. It is a beautiful sight. But you would not have wanted to witness, at close quarters, its creation.
第谷•佈雷赫是16世紀的丹麥天文學家，月球表面的那座環形山就是以他的名字命名。此山在靠近月球的南極，跨度達85公里。周圍是覆蓋南半球的連綿的火山噴出物，這表明在形成此山時的撞擊有多麼劇烈。據估計，此山剛有1億年的歷史（阿波羅17號曾帶回其地質樣品，並以此計算出年代），Bottke說，這是在月球偶遇Baptistina的第一個進入太陽系內部的後代時產生的結果。此景甚是壯觀，但估計你並不想實地見證其形成過程。
1.6億年前隕石 滅絕恐龍
【張翠蘭╱綜合外電報導】6500萬年前隕石撞地球，是導致恐龍滅絕的主要學說之一，不過昨天最新《自然》期刊發表的新佐證報告進一步指出，此厄運早已注定，因為該顆「殺手」隕石是1.6億年前兩顆小行星撞擊的產物。
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「殺手」隕石從中生
科學界一般相信6500萬年前一顆隕石撞擊地球，在墨西哥猶加敦半島形成直徑約180公里隕石坑，導致恐龍滅絕。如今美國西南研究院太空研究部的科學家，
認為該顆隕石有90％可能來自距離地球1.8億公里的巴堤斯帝納(Baptistina)星系。波特克(William
Bottke)博士說：「這顯示即使發生在離地球很遠的事件，仍會對地球生物及地質進化，有重大影響。」
研究團隊指出，1.6億年前一顆直徑170公里的小行星母體，被另一顆直徑60公里的小行星撞擊，碎成逾10萬個碎塊，形成巴堤斯帝納星系，
20％碎塊飛散進入內太陽系，其中2％擊中地球，包括該顆「殺手」隕石。科學家判斷月球上1.08億年前形成的第谷坑，有70％可能性也是該起隕石撞擊下
產物。
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