震驚！穀神星上竟發現有機物

01-27

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文章來源：http://www.skyandtelescope.com/astronomy-news/scientists-find-organics-on-ceres-1602201723/

下面是正文

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Reporting in the February 17th Science, Maria Cristina De Sanctis (INAF Institute for Space Astrophysics and Planetology, Italy) and other members of NASA』s Dawn mission have found a big patch of organic compounds high in the northern hemisphere of the dwarf planet Ceres. Ceres is the largest member of the asteroid belt, and the Dawn spacecraft has been exploring it since 2015.

2月17日科學雜誌報導，Maria Cristina De Sanctis（來自INAF，Istituto Nazionale di Astrofisica，義大利國立天體物理研究所）和NASA的「曙光」號任務的其他參與者們在矮行星穀神星的北半球高緯度地區發現了一大塊含有有機化合物的土壤。穀神星是小行星帶中最大的天體，「曙光」號自2015年就開始對它進行研究、探索。

Organics are not surprising in of themselves. Scientists have found them in meteorites (many of which come from asteroids), and we』ve also seen hints of them on the main-belt asteroids 24 Themis and 65 Cybele. But the signal Dawn picked up is much clearer than the ones from those other asteroids.

有機物本身並不足為奇。科學家們已經在隕石（大都來自於小行星）和小行星帶天體司理星（24 Themis）和原神星（65 Cybele）中發現了有機物。但是這次「曙光」號發現的有機物信號要遠比之前的結果清晰得多。

The organics drape over the southwest floor and rim of the 50-km-wide crater Ernutet, with a few blobs nearby. However, the compounds don』t look to be connected to the crater itself; theyre spread across about 1000 ${rm km^2}$ . Dawn also detected at least one more, much smaller deposit in Inamahari Crater, about 400 km from Ernutet.

被發現的有機物主要覆蓋在50km寬的Ernutet隕石坑的西南角的坑底和邊緣，在這附近也有斑點狀的分布。不過，這些化合物看起來和隕石坑本身沒有什麼聯繫——它們的分布範圍超過1000 ${rm km^2}$ .。此外，「曙光」號還在距離Ernutet約400km的Inamahari隕石坑發現了至少一塊更小的有機化合物沉積物。

These Dawn spacecraft data show a region around the crater Ernutet on Ceres where scientists have discovered concentrations of organic material (labeled 「a」 through 「d,」 two more in this area not shown). The color coding shows the strength of the organics spectral absorption band, with warmer colors indicating the highest concentrations.
這些「曙光」號飛船的數據展示了穀神星上的Ernutet隕石坑的附近區域。在這片區域，科學家們發現了有機物集中分布的跡象，編號從a到d，且還有兩塊分布區域沒有在圖中。色標標識著有機物的光譜吸收波段，暖色意味著有機物分布較為集中。
圖片版權所有：NASA / JPL-Caltech / UCLA / ASI / INAF / MPS / DLR / IDA）

Unfortunately, the scientists couldn』t actually tell what the stuff is, just that it looks like aliphatic organic material. Aliphatic and aromatic are two types of compounds. Aromatic organics have molecular rings of carbon atoms and are fairly 「processed,」 chemically speaking; aliphatic compounds instead generally have straight chains of carbon atoms and have been less affected by heat and radiation.

不幸的是，科學家們並搞不清楚這些有機物到底是啥，只是覺得這大概是脂肪族（謝謝@張俊峰指正）的有機物。脂肪族和芳香族是兩類化合物。芳香族化合物一般含有碳原子環，從化學上講，算是「加工」過的；脂肪族化合物則一般含有展開的碳原子直鏈，受熱和輻射的影響較小。

There are two reasons the result is interesting. One, Ceres also has tons of water ice, plus carbonates and salts. The addition of organic material makes the dwarf planet a promising environment for prebiotic chemistry.

之所以說這一結果很有趣，主要有兩個原因。首先，穀神星上有數以噸計的水冰、碳酸鹽和氯化鈉。有機物的發現說明這顆矮行星擁有典型的前生命起源時期的化學環境。

Two, the organics don』t seem to have been delivered by impacts — no clear cause-and-effect with particular craters, plus a hit probably would have distributed the stuff in diluted form along with other debris. Not to mention there』s other, clearly native material mixed in. Instead, the organics likely come from Ceres itself. Perhaps they』ve been brought up from below by some process, although how remains an open question. Scientists also recently suggested the little world might have a history of ice volcanoes, so maybe it』s more active than we suspected.

再者，這些有機物看起來並不是被撞擊帶來的——它們與任何隕石坑都沒有明顯的因果關聯，且撞擊帶來的有機物應當以稀釋的形式存在，且應當有其他碎片。再說了，在這些有機物中，很明顯混合著本土的物質。所以說，這些有機物看起來來源於穀神星自己。也許它們被某些地質進程從地下帶到了地表——儘管究竟是什麼進程尚且存疑。事實上，有科學家最近提出，體積較小的星球可能有冰火山歷史，所以它們可能有比我們所設想的更加活躍的地質活動。

Read more about the result in the Southwest Research Institute』s press release. Youll find an in-depth recap of Dawns discoveries in our December 2016 issue.

Reference: M. C. De Sanctis et al. 「Localized aliphatic organic material on the surface of Ceres.」 Science. February 17, 2017