Mercury rising 水星升起

本帖最后由 klavier 于 2011-3-19 07:17 编辑 Planetary exploration行星探测 Mercury rising 水星升起 The latest mission to Mercury will map an enigmatic planet in detail  最新水星任务将详细绘制这颗神秘行星的地图 Mar 17th 2011 | from the print edition  EVEN by the standards of space travel, it has been a long, strange trip. But now it should be over. If all went according to plan, at one o'clock in the morning of March 18th―shortly after The Economist went to press―Messenger will have settled into orbit around Mercury, the planet closest to the sun. It is the end of a journey that has taken the craft, launched in 2004 by NASA, America's space agency, past Earth once, Venus twice and Mercury itself three times already. It is also the beginning of an intense scrutiny of the tiny world, which has otherwise remained unvisited by spacecraft since Mariner 10 zoomed past it in the 1970s.  既使按太空旅行的标准来看，这也是一次漫长而奇怪的旅行。但现在这次旅行要结束了。如果一切都按计划来，信使号将在3月18日凌晨1点（《经济学人》刚付印不久）进入水星轨道运行，而水星是离太阳最近的行星。这是该飞船的最后旅程，它由美国宇航局于2004年发射，已经路过地球一次，金星两次以及水星本身三次。这也是对这颗小小行星展开周密调查的开始，该行星自从20世纪70年代水手10号疾掠而过后，还没有飞船以其它方式访问过。 The trip has taken so long because exploring the inner solar system is a tricky business. Gravity accelerates spacecraft as they fall towards the sun. Without its six fly-bys―which used the gravitational fields of the planets involved to counter that effect―Messenger could not have slowed sufficiently to allow it to drop into its intended orbit. Despite the difficulty of getting there, though, Mercury is a juicy target. Since the great reclassification of astronomical objects in 2006, which saw Pluto lose its planetary status, Mercury has been listed as the smallest planet in the solar system. It is also the second densest, has the oldest planetary surface (parts of which seem to date back almost to the formation of the solar system, 4.5 billion years ago) and experiences the most dramatic daily temperature fluctuations. The mercury, as it were, can hit 400ºC when the sun is above the horizon, yet dips below -150ºC at night. 此行花了这么长的时间是因为探索太阳系内部是一件棘手的事。当航天器向太阳靠近时，重力使其加速。如果没有它的六次近水星飞行（利用能抵消这种影响的行星引力场），信使号就不可能放慢到足以使它落入到预定的轨道。不过撇开到达水星轨道的难度，水星却是一个多趣的目标。由于2006年对天体的重新大排位，冥王星失去了它的行星地位，水星就被列为太阳系中最小的行星。水星也是第二个密度最大的行星，拥有最古老的行星表面（部分表面似乎可以追溯到近乎于45亿年前太阳系的形成），经历着变化最急剧的日温度波动。可以说，水星在太阳位于地平线上时能达到400 º C，而在夜晚时则低于-150 º C。 Messenger has already revealed plenty of tantalising information. Mariner 10 managed to map about 45% of Mercury's surface as it sped past, but Messenger's three fly-bys have filled in the gaps, and there is now a virtually complete map of the place. The surface is a jumble of craters, plains and immense, cliff-like scarps that can be hundreds of kilometres long. Astrogeologists suspect these scarps may be analogous to the wrinkles on a raisin, having formed billions of years ago as the planet's surface cooled and shrank.  信使号已经发现了大量惹人干着急的信息。水手10号在其快速掠过时设法绘制了水星表面大约45％的地图，不过信使号的三次近水星飞行已经填补了空白，现在有了几乎很完整的水星表面地图。水星表面上杂乱地分布着坑洞、平原和巨大的悬崖般的陡坡，陡坡可长达数百公里。太空地质学家猜测这些陡坡可能类似于葡萄干上的皱纹，是在几十亿年前当行星表面冷却收缩时开始形成的。 Indeed, the more that is learnt about Mercury, the more intriguing it becomes. Its density is presumed to indicate a metallic core, probably made mostly of iron. No other explanation is plausible. That core, calculation suggests, takes up around 60% of the planet's volume, making it far larger than the cores of Venus, Earth and Mars, the solar system's other rocky planets. How this has come about is the subject of intense speculation, with three theories jostling for the top spot. Two of these theories hold that Mercury used to be much bigger. Either it was then hit by an asteroid which blasted much of its surface into space, or else the hot, young sun simply vaporised its outer layers. The third theory argues that drag in the dusty nebula from which the solar system formed would have herded the heavier, metal-rich bits of dust in that nebula into orbits close to the sun, and that Mercury eventually condensed from these. Each theory predicts a different mixture of surface rocks. Messenger's instruments should help settle the question and shed more light on the early history of the solar system. 事实上，对水星了解的越多，水星就变得越加引人注目。据推测它的密度表明它的核心是金属的，可能主要由铁制成。没有其它更有说服力的解释。计算表明，水星的核心占其体积的大约60％，远远大于金星、地球和火星这些太阳系其它岩石行星的核心。这个结果怎么来的猜测纷纷，有三种理论稳坐头把交椅。其中两种理论认为，水星过去要大得多。当初它要么是被小行星撞击，其大部分表面爆裂进入太空，要么是因为热，年轻的太阳简单地汽化了其外层。第三种理论则认为，太阳系形成的尘埃星云中的反作用力将会在该星云进入靠近太阳的轨道时把较重的、富含金属的尘埃块聚集在一起，这些尘埃块最终被压缩形成后来大密度的水星。每种理论所预测的组成表面岩石的混合物都不相同。信使号携带的工具应该能帮助我们解决这个问题，并且更清楚地揭示太阳系的早期历史。 There are other mysteries. Neither Mars nor Venus has a magnetic field like the Earth's, which is generated by currents in the planet's molten core. But Mercury does. This field was discovered by Mariner 10. That it was like the Earth's was confirmed in 2008 on one of Messenger's fly-bys. In orbit, the probe will be able to study the field in detail, which should reveal more about Mercury's structure and may suggest how the core has managed to remain molten over the billions of years since the tiny planet was formed. It will also follow up radar data from Earth-based telescopes, which suggest that there may be ice at the planet's poles, locked away from the scorching sun in the bottoms of ancient craters―as is also believed to be the case on the moon.  水星还有其它的奥秘存在。无论是火星还是金星都有同地球一样的磁场，是由行星熔融的核心中的电流产生的。而水星也有。水星磁场是由水手10号发现的。水星磁场同地球的磁场一样，这在2008年信使号的一次近水星飞行中被证实了。探测器将会在轨道上详细研究水星的磁场，这将更多地揭示水星结构，且可能表明自从这颗小小行星形成以来，它的核心如何设法保持了数十亿年的熔融状态。探测器也会跟进补充架设在地球上的望远镜的雷达数据，这表明水星的两极可能存在着冰，被封在远古时期所形成的坑洞底部避开了烈日――我们也相信在月球上存在着同样的情况。 A long to-do list, then. Yet all this attention serves only to show how hard exploring Mercury is. The moon, Mars, Venus, two asteroids and even one of the moons of Saturn have all received the attentions of landing craft. The surface of Mercury, too, was to have been visited in 2020, courtesy of a joint European and Japanese mission called BepiColombo. But that landing was cancelled in 2004, though two orbiters should still make the journey. So, despite all the fresh attention Messenger will give it, Mercury will remain the least-explored of the inner planets for some time yet.  之后会造成一段长期的骚动。然而，这次光顾的一切都只表明探索水星是如何的艰难。月球、火星、金星、两个小行星、甚至连土星的卫星之一都已接受过登陆飞船的光顾。假如水星的表面也将在2020年被到访，这要感谢一项被称为水星探测器的欧日合作任务。但是，2004年取消了这次计划中的登陆，不过仍将有两颗人造卫星登上旅程。因此，撇开信使号将给予的最新光顾的一切，在一段时间内水星仍将保持内行星中被探测最少的记录。 from the print edition | Science and Technology