Sun, Jul 08, 2018 - Page 9 News List

Comet or asteroid? Scientists identify interstellar visitor
彗星抑或小行星?科學家解密星際訪客

The interstellar object, Oumuamua, passing through the solar system in October last year, is shown in this artistic rendering provided by European Southern Observatory.
去年十月行經太陽系的星際物體「歐姆阿姆阿」,在歐洲南天天文台提供的想像圖中呈現的樣貌。

Photo: Reuters
照片:路透

Last year’s visitor from another star system — a cigar-shaped object briefly tumbling through our cosmic neck of the woods — has now been identified as a comet. A European-led team makes the case in the journal Nature on June 27.

Telescopes first spotted the mysterious red-tinged object last October as it zipped through the inner solar system. Since then, astronomers have flip-flopped between comet and asteroid for our first confirmed interstellar guest.

Neither a coma nor tail was spotted, hallmarks of an icy comet. But Italian astronomer Marco Micheli and his team reported that the object’s path and acceleration are best explained not just by gravity, but also gases shedding from a comet.

The release of what’s believed to be gaseous carbon monoxide, carbon dioxide and water applied only a tiny force on the object known as Oumuamua — about 1,000 times smaller than the effect of the sun’s gravity — and barely altered its path, the researchers said. But the team’s measurements “were so precise that we could actually see the change in position caused by the outgassing,” said co-author Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies at Jet Propulsion Laboratory in Pasadena, California.

“It’s a definitely exciting discovery,” said Micheli of the European Space Agency. Micheli said computer models suggest objects typically are ejected during the formation of planetary systems, and that most of these castaways should be comets given their location on the frigid outskirts of their systems. Only a tiny fraction should be asteroids, by scientists’ best calculations. Had it been an asteroid, it would have been “extremely lucky to beat these odds” — or it would have underscored scientists’ misunderstanding of the early solar system, Micheli said.

TODAY’S WORDS
今日單字

1. neck of the woods phr.

鄰近、附近

(lin2 jin4; fu4 jin4)

2. make a case phr.

充分解釋

(chong1 fen4 jie3 shi5)

3. flip-flop phr.

說法反覆、舉棋不定

(shuo1 fa3 fan3 fu4; ju3 qi2 bu2 ding4)

4. comet n.

彗星

(hui4 xing1)

5. asteroid n.

小行星

(xiao3 xing2 xing1)

6. interstellar adj.

星際的

(xing1 ji4 de5))


Discovered by a telescope in Hawaii, Oumuamua is Hawaiian for messenger from afar arriving first, or scout. It’s long gone, as are the chances of knowing conclusively what it was.

The University of Toronto’s Alan Jackson, who reported in March that Oumuamua likely came from a two-star system, remains unconvinced of its true identity. “But this is certainly an interesting new piece of information for us to chew on,” he said in an email.

(AP)

去年曾有來自另一個星系的訪客,形狀如雪茄,短暫地翻滾飛過我們所處的宇宙這一隅附近,日前它被鑑定為一顆彗星。歐洲一組研究團隊在六月二十七日出版的學術期刊《自然》中,對此提出了充分的解釋。

去年十月,這個淡紅色的神祕物體迅速地飛經內太陽系,最初是被多台天文望遠鏡觀測到。從那時起,天文學家一直舉棋不定,無法肯定這位首度獲得證實的星際訪客到底是彗星還是小行星。

這位訪客身上既沒有觀測到彗尾,也沒有彗髮,而這些都是一顆結冰彗星應有的特徵。不過,義大利天文學家馬可‧米歇利和他的研究團隊表示,引力作用以及從彗星散發出的數種氣體,能對這個物體的飛行路徑和加速度提出最佳解釋。

研究人員指出,這顆命名為「歐姆阿姆阿」的物體釋放出據信為氣態的一氧化碳、二氧化碳,以及水等物質,卻僅僅對該物體產生非常微弱的作用力──約是太陽引力作用的千分之一──也幾乎沒有改變它的飛行路徑。不過,共同作者之一保羅‧喬達斯表示:這個研究團隊的測量「實在精準,讓我們能夠準確看出該物體因為排放氣體而導致的位移。」喬達斯是加州帕薩迪納的近地物體研究中心主管,該中心隸屬於美國國家航空暨太空總署噴射推進實驗室。

任職於歐洲太空總署的米歇利則表示:「這絕對是讓人興奮的新發現。」他指出,根據電腦運算模型顯示,在行星系統的形成過程中,經常會彈射出物體,這些被拋離的物體,因位處嚴寒的星系外圍,大多數應該都會是彗星。根據科學家最正確縝密的計算,其中只會有一小部分是小行星。米歇利說,要是「歐姆阿姆阿」真是一顆小行星,那「真是太幸運了,畢竟它的機率微乎其微」,或者它也正好點出科學家對太陽系形成初期的認知有所誤解。

「歐姆阿姆阿」是被夏威夷的一台天文望遠鏡所發現,在夏威夷語中的意思是第一位自遠方抵達的信差,或是斥候與偵察兵。不過現在它已遠走高飛,一併帶走了能夠徹底理解它的機會。

多倫多大學的艾倫‧傑克森,今年三月曾經提出「歐姆阿姆阿」可能是來自一個聯星系統的論點,他對於這個物體的真實身份仍然存疑。不過,他也在電子郵件中表示:「這份研究確實是一個饒富興味的新資訊,值得我們反覆思索。」

(台北時報章厚明譯)

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