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Tailless comets could threaten Earth, but they also offer an explanation of the solar system's earliest days.
無尾彗星可能對地球構成威脅，但也為太陽系的早期形成提供了解釋。
NASA's dart mission was an impressive success.
NASA的“飛鏢”任務取得了重要成功。
On September 26th, using a probe weighing 600kg, it hit Dimorphos, an asteroid 160 metres across that was, at the time, 11m kilometres away from Earth.
9月26日，重達600公斤的“飛鏢”探測器擊中了一顆直徑160米的小行星迪莫弗斯，當時該小行星距離地球1100萬公里。
The purpose was to determine whether asteroids which might otherwise strike Earth could have their paths altered by what is, in effect, a game of cosmic billiards.
其目的是確定可能撞擊地球的小行星是否會因為一場本質上屬于“宇宙臺球”的游戲而改變其運行軌跡。
Though the results are not yet in, it seems likely that they could.
雖然任務結果還沒有公布，這似乎是可行的。
But that depends on seeing them early enough.
但這取決于人類觀測到小行星的時間是否足夠早。
Asteroids have predictable orbits, so cataloguing them is feasible, and is currently being done.
小行星的軌道是可預測的，因此可以對它們進行編目，目前這項任務正在進行之中。
This does not generally apply to comets.
但彗星不同。
Though some (like Halley's) have known orbits, most sweep in from the farthest reaches of the solar system, with little notice of their arrival.
雖然有些彗星(如哈雷彗星)的軌道已經確定，但大多數彗星是從太陽系最遠的地方接近的，人類幾乎無法觀測到它們的來臨。
And that lack of notice applies, a fortiori, to a newly discovered class of them that do not flag up their appearance in the conventional way, by developing a tail.
最重要的是，這種觀測不到的情況在新發現的一類彗星上更加突出，此類彗星和傳統彗星外表不同，不會產生彗尾。
The first Manx comet, so called after the tailless cats of the Isle of Man, was spotted in 2014 by a telescope in Hawaii.
2014年，人類利用夏威夷的一臺望遠鏡發現了第一顆無尾彗星，并將其以馬恩島上的無尾貓命名，稱為“馬恩島貓彗星”。
Since then, several dozen more have been detected.
從那時起，人類又發現了幾十顆無尾彗星。
And, as a meeting of the American Astronomical Society in London, Ontario, heard on October 5th, they are objects of great interest.
正如10月5日在安大略省倫敦市舉行的美國天文學會會議上所稱，人們對無尾彗星非常感興趣。
The chance—albeit remote—that such a comet might hit Earth is one reason.
這種彗星撞擊地球的可能性——盡管很小——是其中一個原因。
Another is that they are a surprising source of evidence for what happened in the solar system's earliest days.
另一個原因出人意料——它們是說明太陽系早期形成發展情況的來源之一。
Manx comets, like their tail-wagging brethren, come from the Oort cloud.
馬恩島貓彗星，和它們帶有慧尾的兄弟一樣，來自奧爾特云。
This is a spherical shell of debris left over from the solar system's formation that is way farther from the Sun than the farthest planet, Neptune, and farther even than the Kuiper belt, a disc-like repository of asteroids and minor planets, the most famous inhabitant of which is Pluto.
這是一個由太陽系形成時遺留下來的碎片組成的球體，它和太陽的距離比離太陽最遠的行星海王星還要遠得多，甚至比柯伊伯帶還遠，柯伊伯帶是一個圓盤狀的小行星聚集區域，其中最著名的是冥王星。
The Oort cloud is thought to contain trillions of icy chunks, some of which, because of a collision or the pull of a passing star, from time to time fall inward.
人們認為奧爾特云包含數以萬億計的冰塊，其中一些由于碰撞或擦肩而過的恒星的引力，不時向太陽系內墜落。
As these inbound bolides approach the Sun, their ice sublimes, gas and dust escape, and a comet spreads its tail.
當這些冰塊接近太陽時，冰塊開始升華、形成氣體和塵埃，一顆彗星就這樣展開了它的尾巴。
A Manx comet, by contrast, is presumably a solid (and thus ice-free) lump of rock.
相比之下，馬恩島貓彗星很可能是一塊固體的(不含冰的)巖石。
A tailed comet on a collision course with Earth might possibly be detected early enough for a successor to dart, stationed in outer space, to rush in and push it out of harm's way.
如果存在一顆會與地球相撞的彗星，會拖尾的彗星可能很快就會被發現，駐扎在外層空間的“飛鏢”的繼任者就能及時趕到，把它推到不會危及地球的地方。
For a Manx comet, the warning time would be hopelessly short.
而如果是馬恩島貓彗星，預警時間將短得令人絕望。
