Neutrinos From Deep Inside Earth Provide a New Picture of the Mantle

The JUNO experiment, located outside the city of Guangzhou in China, is expected to report its first geoneutrino detections this year.

位于中国广州市郊的朱诺实验预计将在今年报告首次探测到中微子。

In a laboratory 2 kilometers underground, a crane lowers Matt Depatie , a detector technologist, through a hatch into a white-walled cavern filled with about 7,000 tons of ultrapure water that glows as blue as wiper fluid in the light.

在地下 2 公里的实验室里，一台起重机将探测器技术专家马特·德帕蒂 (Matt Depatie) 通过舱口降入一个白墙洞穴，里面装满了约 7,000 吨超纯水，这些超纯水在灯光下发出与雨刷液一样的蓝光。

“Splashdown,” Depatie says over a radio as he steps into an inflatable raft waiting below.

“溅落，”德帕蒂一边走进等待在下面的充气筏，一边通过无线电说道。

Normally, the cavern is one of the darkest places on Earth, but today, it is lit up for maintenance, offering us a rare chance to see inside.

通常情况下，这个洞穴是地球上最黑暗的地方之一，但今天，它被点亮以进行维护，为我们提供了难得的机会看到里面。

I peer through the hatch at Depatie as he paddles over to examine the submerged experiment.

当德帕蒂划过去检查水下实验时，我透过舱口看到了他。

He’s inspecting a house-size detector built to catch some of the most elusive particles known to physics: neutrinos.

他正在检查一个房屋大小的探测器，该探测器是为了捕捉物理学中最难以捉摸的粒子：中微子而建造的。

This is the SNO+ neutrino experiment, buried deep within the Creighton mine at Snolab, an underground physics laboratory in Sudbury, Canada.

这是 SNO+ 中微子实验，深埋在加拿大萨德伯里地下物理实验室 Snolab 的 Creighton 矿井内。

SNO+ consists of an acrylic sphere lined with nearly 10,000 sensitive light detectors and filled with 780 tons of oily liquid scintillator, which flashes when lit up by energetic particles.

SNO+由一个丙烯酸球体组成，球体上排列着近10,000个灵敏的光探测器，并填充了780吨油状液体闪烁体，当被高能粒子照亮时闪烁体会闪烁。

The water around the device and the rock above it shield the detector from the glare of cosmic radiation, allowing the flickers of less common particle interactions to shine through.

设备周围的水和其上方的岩石保护探测器免受宇宙辐射的眩光，从而使不常见的粒子相互作用的闪烁能够透过。

Our whole journey down has been part of the crusade to maintain absolute darkness, even beyond the visible spectrum of light.

我们的整个旅程都是维持绝对黑暗（甚至超出可见光谱）的十字军东征的一部分。

As we descended the main shaft and walked through a rocky tunnel to the lab, our bodies and clothes collected minute amounts of radioactive radon dust.

当我们沿着主轴下降并穿过岩石隧道到达实验室时，我们的身体和衣服收集了微量的放射性氡尘。

Before entering the main laboratory space, we tossed our mine clothes, showered, and changed into electric blue jumpsuits and hairnets to minimize the contamination we carried in with us.

在进入主实验室空间之前，我们扔掉了矿服，冲了个澡，换上了电蓝色连身裤和发网，以尽量减少随身携带的污染。

“The showers aren’t for you,” Depatie said as we changed, “they’re for the science.”

“淋浴不是为了你，”我们换衣服时德帕蒂说，“它们是为了科学。”

Matt Depatie, left, helps maintain the SNO+ detector, which reuses components of the SNO experiment that ran from 1999 to 2006.

马特·德帕蒂（左）帮助维护 SNO+ 探测器，该探测器重复使用了 1999 年至 2006 年进行的 SNO 实验的组件。

Such extremes are necessary when you’re trying to catch ghosts — in this case, ghosts that may help reveal the secrets of inaccessible regions deep within the Earth.

当你试图捕捉鬼魂时，这种极端的做法是必要的——在这种情况下，鬼魂可能有助于揭示地球深处难以到达的区域的秘密。

Neutrinos are the most abundant of all the particles that have mass.

中微子是所有有质量的粒子中数量最多的。

But that mass is tiny: just a millionth the mass of an electron.

但这个质量很小：只有电子质量的百万分之一。

With such little heft and a neutral electromagnetic charge, the particles hardly ever interact with other matter.

由于质量如此之小且电磁电荷呈中性，这些粒子几乎不与其他物质相互作用。

Trillions of neutrinos — mostly those produced in the sun — pass through our bodies every second, yet after years of hunting them with detectors such as SNO+, researchers have captured only a few hundred thousand of their precious flashes.

每秒有数万亿个中微子（主要是在太阳中产生的中微子）穿过我们的身体，但经过多年使用 SNO+ 等探测器搜寻中微子，研究人员只捕获到了几十万个珍贵的闪光。

Even more elusive — so much so that after decades of searching, scientists have detected only a few hundred of them — are geoneutrinos.

更难以捉摸的是正中微子，经过数十年的搜寻，科学家们只发现了其中的几百个。

Geoneutrinos are produced in processes that heat the interior of the planet.

地球中微子是在加热地球内部的过程中产生的。

This heat plays a major role in powering the flow of rocks in the mantle, which shapes everything from plate tectonics to Earth’s magnetic field.

这种热量在驱动地幔岩石流动方面发挥着重要作用，它塑造了从板块构造到地球磁场的一切。

It comes from two main sources: heat left over from the planet’s formation, and heat produced by the decay of uranium, thorium, and potassium in the rocks of the mantle and crust.

它有两个主要来源：行星形成留下的热量，以及地幔和地壳岩石中铀、钍和钾衰变产生的热量。

Without this second source, Earth would have long since cooled off and become a tectonically dead planet.

如果没有第二个来源，地球早已冷却并成为一颗构造上死亡的行星。

The SNO+ experiment sits deep underground, shielded from cosmic rays beneath 2 kilometers of rock.

SNO+ 实验位于地下深处，在 2 公里的岩石下免受宇宙射线的影响。

Courtesy of Leo Duquette/SNOLAB

由 Leo Duquette/SNOLAB 提供

In counting geoneutrinos, physicists can get a direct measure of Earth’s vital heat-producing elements.

通过计算地中微子，物理学家可以直接测量地球重要的产热元素。

“It’s the one thing we do that focuses on the Earth,” said Ryan Bayes , a particle astrophysicist at Queen’s University in Ontario who works on SNO+.

“这是我们所做的唯一一件关注地球的事情，”从事 SNO+ 工作的安大略省女王大学粒子天体物理学家 Ryan Bayes 说。

“Everything else we do is more focused on what we receive from other places in the universe.”

“我们所做的其他一切都更关注我们从宇宙其他地方收到的信息。”

The first detection of geoneutrinos, by an instrument in Japan called Kamland, was reported in 2005.

2005 年，日本的一台名为 Kamland 的仪器首次检测到了中微子。

In 2009, the Borexino detector in Italy reported catching several dozen more.

2009年，意大利的Borexino探测器报告称又捕获了数十只。

In November 2025, SNO+ reported its first detection, bumping up the number of observed geoneutrinos by about 50.

2025 年 11 月，SNO+ 报告了首次探测结果，将观测到的中微子数量增加了约 50 个。

What makes the detections at SNO+ special is the experiment’s location: These are the first geoneutrinos measured in the western hemisphere, offering a new perspective on Earth’s radioactive interior.

SNO+ 探测的特殊之处在于实验地点：这些是在西半球测量到的第一个中微子，为地球放射性内部提供了新的视角。

Major uncertainties remain in interpreting the results from these experiments, but researchers’ best estimates suggest that each site is measuring a different flux.

对这些实验结果的解释仍然存在重大不确定性，但研究人员的最佳估计表明，每个地点正在测量不同的通量。

“It could be that that’s the first hint that the mantle is not uniform,” said Mark Chen , a particle astrophysicist at Queen’s University and director of the SNO+ collaboration.

“这可能是地幔不均匀的第一个迹象，”女王大学粒子天体物理学家、SNO+ 合作项目主任 Mark Chen 说。

Geochemists have conventionally assumed that radioactive elements are distributed evenly throughout the mantle, because the flowing rock should mix everything together.

地球化学家通常认为放射性元素均匀分布在整个地幔中，因为流动的岩石应该将所有物质混合在一起。

But the measurements of geoneutrinos in different locations could hint that this is not the case.

但不同地点对中微子的测量可能暗示情况并非如此。

The regions that seem to be producing the most geoneutrinos sit roughly above continent-size blobs of anomalously hot, dense material , known as large low-shear-velocity provinces, or LLSVPs, which seismologists have mapped on either side of the core.

似乎产生最多地中微子的区域大致位于大陆大小的异常热致密物质团的上方，这些物质被称为大型低剪切速度省或LLSVP，地震学家已将其绘制在核心的两侧。

One is under Africa, the other under the Pacific Ocean.

一个在非洲下方，另一个在太平洋下方。

“There may be deep Earth structures in the mantle that are not understood,” Chen said.

“地幔中可能存在尚未被了解的地球深层结构，”陈说。

“It could be that [they] concentrate some kinds of elements.”

“它们可能集中了某些元素。”

Neutrinos could one day offer new insight into the still mysterious origin of these deep structures and, more broadly, the patterns in the mantle that underlie many aspects of the Earth system.

中微子有一天可能会为这些深层结构仍然神秘的起源提供新的见解，更广泛地说，可以为地球系统许多方面的地幔模式提供新的见解。

“It really would be a way to make a chemical map of the Earth’s interior,” said William McDonough, a geochemist at the Chinese Academy of Sciences who has long been a leading voice in the search for geoneutrinos.

“这确实是绘制地球内部化学图的一种方法，”中国科学院地球化学家威廉·麦克多诺(William McDonough)说，他长期以来一直是寻找地中微子的领军人物。

The outstanding question is whether the geoneutrino measurements reveal differences between the areas of mantle below each experiment, or if the imbalance originates in the way the different experiments count their geoneutrinos.

悬而未决的问题是，对中微子的测量是否揭示了每个实验下方地幔区域之间的差异，或者这种不平衡是否源于不同实验计算中微子的方式。

Researchers across the board say there’s still so much uncertainty that it’s impossible to say.

所有研究人员都表示，仍然存在太多不确定性，无法确定。

“If we take it at face value, we could say maybe the western hemisphere has a lot more radioactive material in it than the eastern hemisphere,” McDonough said.

麦克唐纳说：“如果我们从表面上看，我们可以说西半球的放射性物质可能比东半球多得多。”

But there are reasons to be wary of these estimates.

但我们有理由对这些估计保持警惕。

“Are the Italians right?

“意大利人说得对吗？

Are the Japanese right?

日本人说得对吗？

Are they both right?

他们都对吗？

Or is something wrong?” he said.

或者有什么问题吗？”他说。

The Borexino experiment, located at Gran Sasso National Laboratory in Italy, was designed primarily to study neutrinos from the sun.

Borexino 实验位于意大利格兰萨索国家实验室，主要旨在研究来自太阳的中微子。

The uncertainties associated with each detector’s results come from the sorting process that physicists go through to identify geoneutrinos, Bayes said.

贝叶斯说，与每个探测器结果相关的不确定性来自物理学家识别中微子的分类过程。

“They don’t just show up and say, ‘Hi, I’m a geoneutrino.’”

“他们不只是出现并说，‘嗨，我是中微子。’”

Scientists must eliminate signals from particles with too much energy, particles with the wrong measure of a property called helicity, and particles that they expect to see flowing from nuclear reactors.

科学家必须消除来自能量过高的粒子、螺旋性属性测量错误的粒子以及他们期望看到从核反应堆流出的粒子的信号。

They must also eliminate geoneutrinos coming from Earth’s crust, with the largest contribution coming from the area within a few hundred kilometers of the detector.

他们还必须消除来自地壳的中微子，其中最大的贡献来自探测器几百公里范围内的区域。

When those other detections are subtracted from the total count, the geoneutrino signal from the mantle should be all that’s left.

当从总计数中减去这些其他检测结果时，来自地幔的中微子信号应该就是剩下的了。

In general terms, the geoneutrino flux from the mantle seems to be very high at Borexino and very low at Kamland, though the uncertainties are great.

一般来说，来自地幔的中微子通量在博莱西诺似乎非常高，而在卡姆兰则非常低，尽管不确定性很大。

A detailed geological interpretation of the SNO+ results is still in the works, Chen said, but so far scientists see a “pretty in-between” mantle below Canada.

Chen 表示，对 SNO+ 结果的详细地质解释仍在进行中，但到目前为止，科学家们在加拿大下方发现了一个“相当介于两者之间”的地幔。

A particular challenge for SNO+ scientists is understanding the neutrinos coming from the detector’s surroundings, including a basin formed 1.8 billion years ago by a giant impactor.

SNO+ 科学家面临的一个特殊挑战是了解来自探测器周围环境的中微子，其中包括 18 亿年前由巨型撞击体形成的盆地。

“There are lots of unknowns in this geological area,” said Virginia Strati , a researcher at the University of Ferrara in Italy who helped develop a local model of radioactivity for Snolab.

意大利费拉拉大学研究员弗吉尼亚·斯特拉蒂 (Virginia Strati) 表示：“这个地质区域存在很多未知因素。”他帮助 Snolab 开发了当地的放射性模型。

The 20-kiloton JUNO detector began operation in August 2025.

20公斤重的JUNO探测器于2025年8月开始运行。

In addition to catching geoneutrinos, it studies particles that stream from the Taishan and Yangjiang nuclear power plants.

除了捕获中微子之外，它还研究从台山和阳江核电站流出的粒子。

Uncertainty also comes from estimates of the total amount of radioactive material heating the mantle.

不确定性还来自对加热地幔的放射性物质总量的估计。

The flux of geoneutrinos suggests that these elements could contribute anywhere from just a small percentage of its heat to half of it — a discrepancy equivalent to the output of tens of thousands of nuclear power plants.

中微子的通量表明，这些元素可以贡献从一小部分到一半的热量——这一差异相当于数万座核电站的输出量。

Both sources of uncertainty make it even more difficult to detect any differences between the chemical makeup of particular sections of the mantle.

这两种不确定性都使得检测地幔特定部分的化学组成之间的差异变得更加困难。

The difference in the geoneutrino flux expected from various distributions of radioactive elements “is very small, and is hidden in these uncertainties,” Strati said.

斯特拉蒂说，不同放射性元素分布所预期的中微子通量差异“非常小，并且隐藏在这些不确定性中”。

The detection at SNO+ comes at an exciting moment for geoneutrino research: JUNO, another huge neutrino experiment currently collecting data in China, is expected to report its first geoneutrino flux later this year, adding a fourth and notably richer view.

SNO+ 的探测正值中微子研究的一个激动人心的时刻：JUNO 是目前在中国收集数据的另一个大型中微子实验，预计将在今年晚些时候报告其第一个中微子通量，增加第四个、尤其更丰富的观点。

With more than 20,000 tons of scintillator, the experiment — buried under a mountain outside the city of Guangzhou — is so large that it is expected to detect more geoneutrinos in its first year than the combined output of Kamland, Borexino, and SNO+ over decades.

该实验埋在广州市外的一座山下，使用了超过 20,000 吨的闪烁体，其规模如此之大，预计第一年探测到的中微子数量将超过 Kamland、Borexino 和 SNO+ 几十年来探测到的中微子总量。

Clearer estimates of the geoneutrino flux at each experiment could come from more detailed geological data, as well as further geoneutrino counts at each site.

对每次实验的中微子通量的更清晰的估计可以来自更详细的地质数据，以及每个地点的进一步的中微子计数。

However, McDonough says the best thing would be to build a neutrino detector at the bottom of the ocean .

然而，麦克唐纳表示，最好的办法是在海底建造一个中微子探测器。

It’s an idea McDonough has championed for decades .

这是麦克唐纳几十年来一直倡导的想法。

Such a detector would be far from continental rocks, which are rich in radioactive elements; oceanic crust is also thinner and more uniform.

这样的探测器将远离富含放射性元素的大陆岩石；洋壳也更薄、更均匀。

Crust-related uncertainties go down so much that “you are in mantle-only territory,” he said.

他说，与地壳相关的不确定性下降得如此之多，以至于“你正处于仅地幔区域”。

The idea of an ocean-bottom detector, estimated to cost hundreds of millions of dollars , has seen little take-up from government funders to date.

海底探测器的想法估计耗资数亿美元，但迄今为止政府资助者几乎没有采取行动。

But McDonough is hoping he can make something happen in China, which has given the green light to other big geoscience projects .

但麦克唐纳希望他能在中国有所作为，这已经为其他大型地球科学项目开了绿灯。

“It’s very possible,” he said.

“这很有可能，”他说。

Until then, physicists will keep paddling around for answers deep underground.

在那之前，物理学家将继续在地下深处寻找答案。

Get highlights of the most important news delivered to your email inbox

获取发送到您的电子邮件收件箱的最重要新闻的摘要

Quanta Magazine moderates comments to facilitate an informed, substantive, civil conversation.

《Quanta》杂志对评论进行审核，以促进知情、实质性、文明的对话。

Abusive, profane, self-promotional, misleading, incoherent or off-topic comments will be rejected.

辱骂、亵渎、自我推销、误导、语无伦次或偏离主题的评论将被拒绝。

Moderators are staffed during regular business hours (New York time) and can only accept comments written in English.

版主在正常工作时间（纽约时间）有工作人员，并且只能接受英文评论。