Gravity study shows why the moon’s two sides look so different
重力研究揭示了为什么月球的两面看起来如此不同
WASHINGTON, May 14 (Reuters) – An exhaustive examination of lunar gravity using data obtained by two NASA robotic spacecraft is offering new clues about why the two sides of the moon – the one perpetually facing Earth and the other always facing away – look so different.
华盛顿，5 月 14 日（路透社）–利用美国宇航局的两个机器人航天器获得的数据对月球重力进行了详尽的检查，这为为什么月球的两面–一面永远面对地球，另一面总是背对地球–看起来如此不同提供了新的线索。
The data from the U.S. space agency’s GRAIL, or Gravity Recovery and Interior Laboratory, mission indicates that the moon’s deep interior has an asymmetrical structure, apparently caused by intense volcanism on its nearside billions of years ago that helped shape its surface features.
来自美国航天局 GRAIL 或重力恢复和内部实验室使命的数据表明，月球的深层内部具有不对称的结构，显然是由数十亿年前其近侧的强烈火山活动造成的，这有助于塑造其表面特征。
The researchers discovered that the lunar nearside flexes slightly more than the farside during its elliptical orbit around Earth thanks to our planet’s gravitational influence – a process called tidal deformation. This indicates differences in the two sides of the lunar interior, they said, specifically in the geological layer called the mantle.
研究人员发现，由于地球引力的影响，月球近侧在绕地球的椭圆轨道上比远侧弯曲得稍微多一些-这一过程称为潮汐变形。他们说，这表明月球内部两侧的差异，特别是在称为地幔的地质层中。
“Our study shows that the moon’s interior is not uniform: the side facing Earth – the nearside – is warmer and more geologically active deep down than the farside,” said Ryan Park, supervisor of the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory in California and lead author of the study published on Wednesday in the journal Nature.
美国宇航局喷气推进实验室太阳系动力学小组主管瑞安·帕克（Ryan Park）表示：“我们的研究表明，月球的内部并不均匀：面向地球的一面（即近月面）比远月面更温暖，地质活动也更活跃。”位于加州的该研究的主要作者。周三发表在《自然》杂志上。
The moon’s nearside is covered by vast plains, called mare, formed from molten rock that cooled and solidified billions of years ago. Its farside has much more rugged terrain, with few plains.
月球的近侧被巨大的平原覆盖，称为月海，由数十亿年前冷却和固化的熔融岩石形成。它的另一边有更多的崎岖地形，几乎没有平原。
Some scientists have hypothesized that intense volcanism within the nearside that caused radioactive, heat-generating elements to accumulate on that side of the mantle drove the surface differences observed today. The new findings offer the strongest evidence yet to support this notion.
一些科学家推测，近地表强烈的火山活动导致放射性发热元素在地幔的这一侧积聚，从而导致了今天观测到的地表差异。新的发现提供了最有力的证据来支持这一观点。
The researchers estimated that the nearside mantle on average is about 180-360 degrees Fahrenheit (100-200 degrees Celsius) hotter than the farside, with the thermal difference perhaps sustained by radioactive decay of the elements thorium and titanium on the nearside.
研究人员估计，近侧地幔平均比远侧高出180-360华氏度（100-200摄氏度），这种温差可能是由近侧元素钍和钛的放射性衰变维持的。
“The moon’s nearside and farside look very different, as shown by differences in topography, crustal thickness and the amount of heat-producing elements inside,” Park said.
帕克说：“月球的近侧和远侧看起来非常不同，这可以从地形、地壳厚度和内部产热元素的数量上看出来。”
The moon’s diameter of about 2,160 miles (3,475 km) is a bit more than a quarter of Earth’s diameter. The lunar mantle is the layer located beneath the crust and above the core, spanning a depth about 22-870 miles (35-1,400 km) under the surface. The mantle makes up roughly 80% of the moon’s mass and volume and is composed mostly of the minerals olivine and pyroxene, similar to Earth’s mantle.
月球的直径约为2,160英里（3,475公里），略高于地球直径的四分之一。月球地幔是位于地壳之下和地核之上的一层，在地表以下约35- 1，400公里（22-870英里）的深度。地幔约占月球质量和体积的80%，主要由矿物橄榄石和辉石组成，类似于地球的地幔。
“The fact that the detected asymmetry in the mantle matches the pattern of the surface geology – for instance, differences in the abundance of the approximately 3-4 billion-year-old mare basalts (volcanic rock) between the nearside and the farside – suggests that processes which drove ancient lunar volcanism are active today,” said Caltech computational planetary scientist and study co-author Alex Berne, affiliated with the Jet Propulsion Laboratory working on the design of gravity sensors for missions to the outer solar system.
“事实上，地幔中检测到的不对称性与地表地质的模式相匹配-例如，大约 30 – 40 亿年前的月海玄武岩丰度的差异（火山岩）在近端和远端之间-表明驱动古代月球火山活动的过程今天仍然活跃，”加州理工学院计算行星科学家和研究合着者 Alex Berne 说，该公司隶属于喷气推进实验室，致力于设计外太阳系飞行任务的重力传感器。
The researchers spent years analyzing data from GRAIL’s Ebb and Flow spacecraft, which orbited the moon from December 2011 to December 2012.
研究人员花了数年时间分析 GRAIL 的 Ebb and Flow 航天器的数据，该航天器于 2011 年 12 月至 2012 年 12 月绕月运行。
“Our study delivers the most detailed and accurate gravitational map of the moon to date,” Park said.
“我们的研究提供了迄今为止最详细，最准确的月球引力图，”帕克说。
“This enhanced gravity map is a critical foundation for developing lunar Positioning, Navigation and Timing (PNT) systems, which are essential for the success of future lunar exploration missions. By improving our understanding of the moon’s gravity field, it contributes to establishing a precise lunar reference frame and time system, enabling safer and more reliable navigation for spacecraft and surface operations,” Park added.
“这张增强的重力图是开发月球定位、导航和定时（PNT）系统的关键基础，这对未来月球探测任务的成功至关重要。通过提高我们对月球重力场的理解，它有助于建立精确的月球参考系和时间系统，为航天器和表面操作提供更安全，更可靠的导航。
The same approach employed here using gravity data to assess the lunar interior, the researchers said, could be applied to other bodies in the solar system such as Saturn’s moon Enceladus and Jupiter’s moon Ganymede, two worlds of interest in the search for potential life beyond Earth.
研究人员说，这里使用重力数据来评估月球内部的相同方法可以应用于太阳系中的其他天体，例如土星的卫星 Enceladus 和木星的卫星 Ganymede，这两个世界在寻找地球以外的潜在生命方面很有意义。
In the meantime, the new findings add to the understanding of Earth’s eternal companion.
与此同时，新的发现增加了对地球永恒伴侣的理解。
“The moon plays a vital role in stabilizing Earth’s rotation and generating ocean tides, which influence natural systems and daily rhythms,” Park said. “Our knowledge of the moon has expanded through human and robotic missions that have revealed details about its surface and interior, yet many questions about its deep structure and history remain. As our closest neighbor, the moon continues to be an important focus of scientific discovery.”
帕克说：“月球在稳定地球自转和产生海洋潮汐方面起着至关重要的作用，海洋潮汐影响着自然系统和日常节奏。”“通过人类和机器人任务，我们对月球的了解已经扩大，这些任务揭示了月球表面和内部的细节，但有关其深层结构和历史的许多问题仍然存在。作为我们最近的邻居，月球仍然是科学发现的重要焦点。”