出乎意料！月球上发现了一块巨大的花岗岩

2023-07-19 16:07

标题
Not that sort of monolith
不是那种巨石
An enormous—and unexpected—lump of granite has been found on the Moon
月球上发现了一块巨大的花岗岩--出乎意料

The discovery sheds light on lunar history, and suggests how other moons might be explored
这一发现揭示了月球的历史，并提出了探索其他卫星的方法

正文

IN “2001: A SPACE ODYSSEY”, Stanley Kubrick and Arthur C. Clarke imagined a monolith buried beneath the surface of the Moon which turned out to be an alien artefact that set humankind on a path to the stars. The “batholith” that has been discovered below Compton-Belkovich, a volcanic-looking set of features on the far side of the Moon, hardly promises that. But it sheds some interesting light on the Moon’s past, and shows the power of a new way of peering into the crusts of other planets.

斯坦利-库布里克（Stanley Kubrick）和阿瑟-克拉克（Arthur C. Clarke）在《2001：太空漫游》（2001: A SPACE ODYSSEY）中想象了一块埋藏在月球表面下的巨石。在康普顿-贝尔科维奇（Compton-Belkovich）下面发现的 "浴石"--月球远侧的一组火山岩地貌--很难让人相信这一点。但它揭示了月球过去的一些有趣的信息，并显示了一种窥探其他行星地壳的新方法的威力

A batholith is a geological formation created when a vast quantity of molten rock rises through a planet’s crust, spreading out sideways as it does so. On Earth, these batholiths are composed mostly of granite; the rocks of Yosemite, for example, are parts of the Sierra Nevada batholith uncovered and spectacularly sculpted by subsequent erosion.

熔岩是一种地质构造，当大量熔岩在行星地壳中上升，并向两侧扩散时就形成了熔岩。在地球上，这些熔岩主要由花岗岩组成；例如，优胜美地的岩石就是内华达山脉熔岩的一部分，这些熔岩在随后的侵蚀作用下被揭露出来，形成了壮观的雕刻。

The Compton-Belkovich batholith is also made of granite, which is what gave it away. Granite is richer in thorium than other igneous—that is, once molten—rocks, such as basalt, and thorium is radioactive. Its decay heats the granite that hosts it. Measurements of microwave emissions made by the first two Chinese satellites to orbit the Moon, Chang’e 1 and Chang’e 2, allowed a team of scientists led by Matthew Siegler and Jianqing Feng of the Planetary Science Institute in Tucson, Arizona and Southern Methodist University in Dallas, Texas to calculate how much heat was being given off by rocks under the surface at Compton-Belkovich.

康普顿-贝尔科维奇岩床也是由花岗岩构成的，这就是它的秘密所在。花岗岩比其他火成岩（即曾经熔融的岩石，如玄武岩）富含钍，而且钍具有放射性。钍的衰变会加热容纳它的花岗岩。由亚利桑那州图森市行星科学研究所的马修-西格勒（Matthew Siegler）和冯建青（Jianqing Feng）以及得克萨斯州达拉斯市南卫理公会大学（Southern Methodist University）的冯建青领导的科学家小组通过对中国首批两颗绕月卫星--嫦娥一号和嫦娥二号--发射的微波进行测量，计算出了康普顿-贝尔科维奇表面下的岩石释放出多少热量。

Assuming that the thorium was present at the sort of concentrations typically seen in granite allowed the scientists to calculate a likely shape for the source. Their best guess, published in Nature last week, was that there is one smallish hot blob, maybe 10-20km across and a few kilometres deep, balanced on top of a much bigger, deeper one that might be 50km across and go down for tens of kilometres.

假设钍在花岗岩中通常存在的浓度，科学家们就能计算出热源的可能形状。他们的最佳猜测发表在上周的《自然》（Nature）杂志上，即有一个直径约 10-20 千米、深几千米的小热球，平衡在一个直径约 50 千米、深几十千米的更大更深的热球之上。

This suggests interesting goings-on in the depths of the Moon of a sort not previously recognised. Igneous rocks are made through a sort of geological distillation. When rocks far below the surface are heated, some components melt more easily than others; when the molten rock solidifies its mineral make-up is not the same as that of the original parent.

这表明月球深处发生了有趣的变化，而这种变化是以前从未认识到的。火成岩是通过一种地质蒸馏法形成的。当远在地表以下的岩石被加热时，某些成分比其他成分更容易熔化；当熔岩凝固时，其矿物组成与原始母体的矿物组成并不相同。

To turn rock from the mantle of Earth, or the Moon, into basalt requires just one cycle of distillation; basalt thus created makes up the solid crust under the oceans of Earth and the smooth lava plains of the Moon. To make granite, though, requires a number of separate distillations (which is what gives it high thorium concentrations). On Earth this is easily arranged; the collisions of tectonic plates provides lots of opportunities. On the placid, plateless Moon there is no such mechanism, and it has been easy to assume that basalt is for the most part all the planet has to offer. The granite batholith suggests something new at play. Perhaps the rocks in the area were unusually rich in water. Perhaps pulses of heat from below made them melt and freeze repeatedly.
将地球或月球地幔中的岩石转化为玄武岩只需要一个蒸馏周期；这样形成的玄武岩构成了地球海洋下的固体地壳和月球上光滑的熔岩平原。不过，要制造花岗岩，则需要多次单独的蒸馏（这也是花岗岩钍浓度高的原因）。在地球上，这很容易安排；构造板块的碰撞提供了很多机会。在没有板块的平静月球上，没有这样的机制，人们很容易认为玄武岩是地球上的全部。花岗岩熔岩表明有新的东西在起作用。也许该地区的岩石含有异常丰富的水。也许来自地下的热脉冲使它们反复融化和冻结。

The lunar discovery suggests that similar microwave measurements might provide novel insights into the innards of other planets. That this has not been tried before is due to a preconception. Satellites orbiting Earth use microwave receivers to measure water in the atmosphere. Because the solar system’s other rocky planets do not have watery atmospheres, such instruments have not been sent to them.
月球上的发现表明，类似的微波测量可能会让人们对其他行星的内部结构有新的认识。以前之所以没有尝试过，是因为先入为主。围绕地球运行的卫星使用微波接收器测量大气中的水。由于太阳系的其他岩质行星没有含水的大气层，因此还没有向它们发送过此类仪器。

But when China launched Chang’e 1 and 2 its aim was to show that it could do science round the Moon, not necessarily to do the best such science. Dr Siegler thinks the microwave antennae were put on board simply because they had been shown to work and there were no more suitable instruments to hand. Now they have proved their worth, he hopes to see the designers of future spacecraft take note. One target where they might come in handy would be the moons of Jupiter, where their sensitivity to heat and moisture might be a useful addition to other sub-surface probes. Fans of “2001” will remember that its monolith spurred a new mission to Jupiter. Maybe the batholith will, too. ■

但是，中国发射嫦娥一号和二号的目的是为了证明它可以在月球上进行科学研究，而不一定是要进行最好的科学研究。Siegler博士认为，在月球上安装微波天线只是因为它们已经被证明是有效的，而且手头也没有更合适的仪器。现在它们已经证明了自己的价值，他希望看到未来的航天器设计者注意到这一点。木星卫星是它们可能派上用场的一个目标，它们对热量和湿度的敏感性可能会成为其他地表下探测器的有益补充。2001》的影迷们一定还记得，该片中的一块巨石推动了一项前往木星的新任务。也许浴石也会如此。■

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