Scientific American 60-second Science, July 4, 2016
作者：Lee Billings 翻譯整理：SophieMen
原文地址：Is Mars Missing a Moon? - Scientific American
Transript and Translation
Mars is a planet of outsized splendor. Despite being only half as big and a tenth as heavy as Earth, it bears the solar system’s tallest mountain, longest canyon and largest crater. At 22 and 12 kilometers wide, however, its inner moon Phobos and outer moon Deimos are figurative small potatoes. Scientists suspect both formed much as Earth’s single large moon did, from a massive debris disk ejected into orbit by a giant impact eons ago. But if Mars’s moons formed like Earth’s, why are they so very much smaller?
火星是一個(gè)有著迷人光暈的星球。盡管它的大小只有地球的一半、質(zhì)量只有地球的十分之一，火星卻有著太陽(yáng)系最高的火山、最長(zhǎng)的峽谷和最大的火山口。火星的兩顆衛(wèi)星，內(nèi)側(cè)的Phobos和外側(cè)的Deimos，直徑分別是22千米和12千米，被比喻成小土豆?？茖W(xué)家們懷疑這兩顆衛(wèi)星都像地球的唯一衛(wèi)星月球一樣，是由億萬(wàn)年前在一次巨大沖擊中被射入軌道的一個(gè)大質(zhì)量碎片形成的。但是如果火星的衛(wèi)星的形成方式和地球的衛(wèi)星一樣，為什么相比而言火星的衛(wèi)星小這么多呢？
The answer may be that they did not form alone. New simulations from Pascal Rosenblatt of the Royal Observatory of Belgium and colleagues show how the debris disk from a giant impact on Mars could have generated additional moons a few hundreds of kilometers in size. After forming in the dense inner regions of the disk, those larger moons would have stirred the disk’s sparser outer reaches, allowing smaller companions like Phobos and Deimos to coalesce from the ripples. The study appears in the journal Nature Geoscience. [Rosenblatt et al., Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons]
答案或許是因?yàn)樗麄儾⒉皇仟?dú)自形成的。比利時(shí)皇家天文臺(tái)的Pascal Rosenblatt和他的同事們進(jìn)行的新仿真顯示，在火星一次巨大沖擊產(chǎn)生的碎片形成了幾百千米大小的衛(wèi)星。在碎片的高密度內(nèi)核形成后，那些大衛(wèi)星攪動(dòng)著碎片稀疏的延伸區(qū)域，使得更小的如同Phobos和Deimos這樣的伴隨星在漣漪中合并。這一研究發(fā)表在《自然·地球科學(xué)》期刊上[Rosenblatt et al., Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons]。
In this scenario, the reason we only see Phobos and Deimos today is that the bigger moons were destroyed a few million years after their formation. Their low, fast orbits outpaced Mars’s rotation, creating a tidal pull that sent them spiraling down to crash into the planet (Earth’s moon, by contrast, orbited slower than our planet’s rotation, allowing it to spiral outward and survive). Future investigations could test the new hypothesis by looking for clusters of Martian craters produced by the infalling moons, but in the meantime, proof that Mars can kill its companions is right before our eyes: The orbit of Deimos is stable, but Phobos is in a death spiral, losing two centimeters of altitude per year to Mars’s tidal pull. It will plunge into the planet in 20 [million] to 40 million years, leaving lonely, far-out Deimos as the last vestige of what may have been a once-mighty system of Martian moons.
在這一場(chǎng)景中，我們今天只能看到Phobos和Deimos的原因是更大的衛(wèi)星在形成幾百萬(wàn)年后被毀滅了。他們?cè)谟挚煊值偷睦@行中超越了火星自轉(zhuǎn)的速度，形成了一種能夠使他們螺旋下降墜落行星的潮汐力（相反，地球的衛(wèi)星，繞行速度低于行星自轉(zhuǎn)，使得衛(wèi)星螺旋遠(yuǎn)離從而一直存在）。未來的研究可能通過尋找火星上由墜落衛(wèi)星形成的火山口群來對(duì)這一新假設(shè)進(jìn)行檢驗(yàn)；但是同時(shí)，火星能夠殺死它的伴星的證據(jù)就在我們眼前——Deimos的軌道是穩(wěn)定的，但是Phobos卻在死亡螺旋之中，在火星的潮汐力作用下其高度每年下降2厘米。它將會(huì)在兩千萬(wàn)年到四千萬(wàn)年內(nèi)墜入火星，留下Deimos——作為曾經(jīng)強(qiáng)大的火星衛(wèi)星們的最后遺跡——孤獨(dú)而珍貴的存在著。
Vocabulary
splendor, \?splen-d?r, noun, 1. great and impressive beauty. 2. things that are very beautiful or impressive.
canyon, \?kan-y?n, noun, a deep valley with steep rock sides and often a stream or river flowing through it.
crater, \?krā-t?r, noun, 1. a large round hole in the ground made by the explosion of a bomb or by something falling from the sky. 2. the area on top of a volcano that is shaped like a bowl
figurative,\?fi-g(y)?-r?-tiv, adjective, 1. used with a meaning that is different from the basic meaning and that expresses an idea in an interesting way by using language that usually describes something else : not literal. 2.showing people and things in a way that resembles how they really look : not abstract.
debris, \d?-?brē, noun, 1.the pieces that are left after something has been destroyed. 2.things (such as broken pieces and old objects) that are lying where they fell or that have been left somewhere because they are not wanted.
far-out, \?f?r-?au?t, adjective, very strange or unusual.
