http://www.universetoday.com/2009/04/10/spacecraft-searching-for-remains-of-mystery-planet/#more-28885
April 10th, 2009
Spacecraft Searching for Remains of Mystery Planet
Written by Nancy Atkinson
Sun-Earth Lagrange points. The STEREO probes are about to pass throughL4 and L5. Solar observatories often park themselves at L1 while deepspace observatories prefer L2. Credit: NASA
太阳——地球间的拉格朗日点。双子卫星探测器大概会飞越L4和L5点。太阳研究者常常把卫星置于L1点，而深空观测者更喜欢L2点。版权：NASA(本图比例显然是示意——译注)
How did our Moon form? The leading hypothesis, the Giant Impact Theory, proposes that in the formative years of the Solar System, a Mars-sizedprotoplanet crashed into Earth. Debris from the collision, a mixture ofmaterial from both bodies, spun out into Earth orbit and coalesced intothe Moon.Soon,this theory will be tested, perhaps answering the question of how ourMoon was born. Two identical NASA spacecraft are preparing to enterareas in space known as the Lagrangian points where remains of thismystery protoplanet may be hiding. The spacecraft duo, called SolarTerrestrial Relations Observatory, or Stereo, will pass by the L4 andL5points where the gravity of the sun and Earth combine to form gravitational wells where asteroids and space dust tend to gather.
我们的月球来自何方？根据现在主流的大碰撞假说，在太阳系初步形成的年月，一个火星大小的原行星与原始地球猛烈碰撞（真正的火星撞地球哦——译注）。碰撞产生的碎片中，最大的一块被拉入地球轨道并最后合并碎片形成了月球（由此，月球包含了原始地球和那个原行星的物质）。不久的将来，这个假说就将被检验，或许还能同时解答我们的月球来源问题。NASA将发射2个完全相同的航天器到天空中的拉格朗日点，去寻找那个神秘行星的遗迹（拉格朗日点是那个神秘行星残余最可能的藏身处）。这2个双重探测器，称为太阳——地球关系观察者，简称STEREO，将飞越L4和L5点。前面说过，拉格朗日点是太阳——地球相互之间的引力平衡点，此处是小行星和太空尘埃容易聚集的所在。
During their journey, the two spacecraft will use a wide-field-of-view telescopeto look for asteroids orbiting the region. Scientists will be able toidentify if a dot of light is an asteroid because it will shift itsposition against stars in the background as it moves in its orbit.
在旅程中，双子探测器将使用宽视野望远镜探测该区域小行星的轨道。科学家能够鉴别出小光点是不是小行星，因为它们会在恒星背景上沿各自的轨道移动。
The Giant Impact Theory explains many aspects of lunar geology including the size of the Moon’score and the density and isotopic composition of moon rocks. Amodification of the Giant Impact Theory is the “Theia hypothesis,”abrainchild of Princeton theorists Edward Belbruno and Richard Gott.
大碰撞假说能够解释月质学的许多方面内容，包括月球核心的大小、密度、月岩的同位素组分等。大碰撞假说的一个修正版是“忒伊亚假说”，它由普林斯顿大学的Edward Belbruno和Richard Gott共同提出。
“About 4.5 billion years ago when the planetswere still growing,” said Michael Kaiser, Stereo project scientist atGoddard Space Flight Center, “a hypothetical world called Theia mayhave been nudged out of L4 or L5 by the increasing gravity of otherdeveloping planets like Venus,sendingit on a collision course with Earth. The resulting impact blasted theouter layers of Theia and Earth into orbit, which eventually coalescedunder their own gravity to form the moon.”
戈达德太空飞行中心双子探测器项目组科学家Michael Kaiser（迈克尔 凯撒）说：“大约45亿前，当行星们还在发育阶段，假设一个原先在L4或L5点的原行星胚（忒伊亚），受正在发育的其他原行星引力摄动而撞向地球。碰撞结果，忒伊亚和地球的外层物质被抛入环绕地球的轨道，并最终在自身引力下聚合为月球。”
The 18th-century mathematician Joseph-Louis Lagrange realized there were five such wells in the sun-Earth system. The twin probes are approaching L4 and L5.
18世纪的法国数学家约瑟夫·路易斯·拉格朗日就已经计算出在日—地系统中，存在5个（引力）平衡点。双子探测器将靠近L4和L5点。
“These points may hold small asteroids, which could be leftovers from aMars-sized planet that formed billions of years ago,” said Kaiser.
“这些点附近可能存在着小行星，它们可能是数十亿年前火星大原行星的残余”，凯撒说。
Deployment of STEREO Spacecraft Panels. Credit: 2002-Johns HopkinsUniversity Applied Physics Laboratory. Credit: Dr C.J.Eyles, Universityof Birmingham
双子探测器计划示意图 版权：(马里兰州)约翰·霍普金斯大学应用物理实验室2002级，英国伯明翰大学C.J.Eyles教授
The theory explains puzzling properties of the moon, such as itsrelatively small iron core. At the time of the giant impact, Theia andEarth would have been large enough to be molten, enabling heavierelements, like iron, to sink to the center to form their cores. Animpact would have stripped away the outer layers of the two worlds,containing mostly lighter elements like silicon. The moon eventuallyformed from this material.
大碰撞假说能解释月球的一些令人迷惑的属性，比如它有一个相当小的铁质核心。在大碰撞时产生的巨大热能使地球和忒伊亚融化，这样像铁一类的重金属就能沉入（月球的）核心区。大碰撞同时会把两个星球的外层剥离，外层包含轻得多的元素比如硅。月球最后由这些元素组成。
Stereo’s primary mission is to give three-dimensional views of spaceweather by observing the sun from the two points where the spacecraftare located. Images and other data are then combined for study andanalysis. Space weather produces disturbances in electromagnetic fieldson Earth that can induce extreme currents in wires, disrupting powerlines and causing wide-spread blackouts. It also can affectcommunications and navigation systems. Space weather has beenrecognized as causing problems with new technology since the inventionof the telegraph in the 19th century.
双子探测器的首要任务是在它们的两个观测点上观察太阳，然后形成三维太空环境图。它们观测的图像和数据将汇总并研究分析。太空环境变化会引发地球磁场事件，极端情形下会产生巨大感应电流，导致输电线短路和大范围的停电事故。它也能影响通讯和电子导航系统。自19世纪发明电报这一新技术以来，太空环境公认是电报中断的主要外因。
Sources: Goddard Space Flight Center, Science@NASA |
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