What Crystals Older Than the Sun Reveal About the Start of the Solar System
Presolar grains, found in meteorites, are smaller than a bacterial cell.
陨石中发现的前太阳颗粒比细菌细胞还要小。
The standard story of the origin of our solar system has gone like this: 4.6 billion years ago, a giant cloud of dust hung frozen in space.
关于太阳系起源的标准故事是这样的：46亿年前，一团巨大的尘埃云冻结在太空中。
Then the explosion of a nearby star caused part of that dust cloud to collapse.
然后附近一颗恒星的爆炸导致部分尘埃云塌陷。
Pulled by gravity toward a central point, the dust coalesced into a radiating ball of hydrogen and helium about 1.4 million kilometers in diameter — what would become our sun.
尘埃被重力拉向中心点，凝聚成一个直径约 140 万公里的氢和氦辐射球，也就是我们的太阳。
The remainder, which fell into orbit, collected into our solar system’s planets, along with a mess of asteroids and other cosmic leftovers.
其余的落入轨道，与一堆小行星和其他宇宙残留物一起聚集到我们太阳系的行星上。
To test the validity of this story, researchers need to peer back in time to the solar system’s first moments and beyond.
为了检验这个故事的有效性，研究人员需要回溯太阳系诞生的最初时刻及以后。
And the cosmochemist Nan Liu has a way to do that: Locked in a safe on her desk at Boston University’s Institute for Astrophysical Research is a shard of meteorite flecked with material older than the sun.
宇宙化学家刘楠有办法做到这一点：波士顿大学天体物理研究所办公桌上的保险箱里锁着一块陨石碎片，上面点缀着比太阳更古老的物质。
“It’s the most pristine [type of] meteorite, not altered by water or heat,” Liu said as she took out and held up the specimen — a shiny, dark stone about the size and shape of an arrowhead.
“这是最原始的[类型]陨石，不会因水或热而改变，”刘一边说，一边取出并举起标本——一块闪亮的黑色石头，大小和形状如箭头。
Meteorites like this one formed around the time of the dust cloud collapse.
像这样的陨石是在尘埃云塌陷时形成的。
The collapse of the cloud and the ignition of the sun melted away much of the chemical information contained in the meteorite, but within it some microscopic crystals — smaller than a single bacterial cell — survived intact.
云层的崩塌和太阳的点燃融化了陨石中包含的大部分化学信息，但其中一些比单个细菌细胞还小的微观晶体完好无损地幸存下来。
These crystals, called presolar grains, are far and away the oldest material accessible to us on Earth.
这些晶体被称为太阳前颗粒，无疑是地球上我们所能接触到的最古老的材料。
Nan Liu, a cosmochemist at Boston University’s Institute for Astrophysical Research, holds up a piece of meteorite that contains grains of material older than the sun.
波士顿大学天体物理研究所的宇宙化学家刘南举着一块陨石，其中含有比太阳更古老的物质颗粒。
Over the past decade or so, scientists have used meteorites like Liu’s to challenge the story of how the solar system formed.
在过去十年左右的时间里，科学家们利用刘氏陨石等陨石来挑战太阳系形成的故事。
Instead of a supernova, the solar system and everything in it might owe its existence to a more placid-sounding cosmic scenario: Maybe our solar system cobbled itself together from the winds blown off of a gargantuan star.
太阳系及其中的一切事物的存在可能不是超新星，而是一个听起来更平静的宇宙场景：也许我们的太阳系是由一颗巨大恒星吹来的风拼凑而成的。
New studies of presolar grains could offer a way to determine whether this new story is correct.
对太阳前颗粒的新研究可以提供一种方法来确定这个新故事是否正确。
Scientists got their first clue about what could have triggered the formation of the solar system when a fireball appeared over Mexico in 1969.
1969 年，当墨西哥上空出现一个火球时，科学家们首次获得了关于太阳系形成原因的线索。
The now-famous Allende meteorite spread its debris over more than 500 square kilometers.
现在著名的阿连德陨石散布其碎片超过 500 平方公里。
In 1976, researchers reported that samples from Allende contained a surprise: an unexpectedly large amount of a stable isotope called magnesium-26.
1976 年，研究人员报告称，阿连德的样本中含有令人惊讶的东西：出人意料地含有大量称为镁 26 的稳定同位素。
They proposed that the meteorite formed with an abundance of aluminum-26, which is radioactive and leaves behind magnesium-26 when it decays.
他们提出，陨石中含有丰富的铝 26，铝 26 具有放射性，衰变时会留下镁 26。
Yet aluminum-26 was not known to be a normal component of the interstellar medium — the dusty space between stars that would have provided the materials for Allende.
然而，人们并不知道铝 26 是星际介质的正常成分，星际介质是恒星之间的尘埃空间，为阿连德提供了材料。
Ordinary stars don’t make that particular isotope.
普通恒星不会产生这种特殊的同位素。
“Most of these isotopes as we observe them in the early solar system, they were just the natural product of galactic chemical evolution,” said Maria Lugaro , an astrophysicist at the Konkoly Thege Miklós Astronomical Institute in Hungary.
匈牙利 Konkoly Thege Miklós 天文研究所的天体物理学家玛丽亚·卢加罗 (Maria Lugaro) 表示：“我们在早期太阳系中观察到的大多数同位素都是银河系化学演化的自然产物。”
“The most important exception is aluminum-26.”
“最重要的例外是铝 26。”
Pieces of the Allende meteorite landed across the Mexican state of Chihuahua.
阿连德陨石碎片落在墨西哥奇瓦瓦州各地。
So where’d it come from?
那么它是从哪里来的呢？
In 1977, two eminent astrophysicists proposed that the anomalous aluminum likely came from a nearby supernova explosion.
1977年，两位著名的天体物理学家提出，异常铝可能来自附近的超新星爆炸。
Other phenomena can produce aluminum-26, but the supernova shock wave could also have caused the collapse of the cloud.
其他现象可以产生铝-26，但超新星冲击波也可能导致云的塌陷。
With a single event, astronomers could explain how two rare occurrences — the injection of aluminum-26 and the formation of a new solar system — happened at virtually the same moment.
通过一次事件，天文学家就可以解释两个罕见的事件——铝26的注入和新太阳系的形成——是如何在几乎同一时刻发生的。
“Everybody felt that we needed something to trigger the collapse,” said Vikram Dwarkadas , an astronomer at the University of Chicago.
“每个人都觉得我们需要一些东西来引发崩溃，”芝加哥大学的天文学家维克拉姆·德瓦卡达斯说。
The supernova trigger remained the favored scenario for decades , supported by detailed astrophysical models, as well as further measurements of enriched magnesium-26 in pristine meteorites.
几十年来，在详细的天体物理模型以及对原始陨石中富集镁 26 的进一步测量的支持下，超新星触发仍然是人们所青睐的场景。
But over the past decade or so, that view has run up against other measurements that don’t seem to match.
但在过去十年左右的时间里，这种观点与其他似乎不相符的衡量标准发生了冲突。
The problem: The solar system has an iron deficiency.
问题是：太阳系缺铁。
Supernovas don’t just make aluminum.
超新星不仅仅生产铝。
Any nearby supernova would likely also have injected lots of the radioactive isotope iron-60.
任何附近的超新星也可能注入了大量的放射性同位素铁60。
Therefore, if a supernova launched the formation of the solar system, “we should see quite high initial [iron-60] abundances in the early-formed objects,” wrote Linru Fang , a cosmochemist at the University of Copenhagen, in an email.
因此，如果超新星引发了太阳系的形成，“我们应该会在早期形成的天体中看到相当高的初始[铁60]丰度，”哥本哈根大学宇宙化学家林如方在一封电子邮件中写道。
Some studies have reported finding enough iron-60 in meteorite samples to support the supernova story.
一些研究报告称在陨石样本中发现了足够的铁 60 来支持超新星的故事。
But not all scientists agree with those findings; several researchers told Quanta that most cosmochemists now think that, while there was an abundance of aluminum-26 at the start of the solar system, there wasn’t much iron-60 after all.
但并非所有科学家都同意这些发现。几位研究人员告诉广达，大多数宇宙化学家现在认为，虽然太阳系初期存在丰富的铝 26，但毕竟铁 60 并不多。
Early last year — in a study described by its authors as the most precise measure of iron-60 in the early solar system to date — Fang and her colleagues reported low levels of iron-60 (measured via its stable decay product nickel-60) in a planetesimal formed just after the collapse of the cloud.
去年年初，方和她的同事在一项被作者描述为迄今为止早期太阳系中最精确的铁 60 测量的研究中报告称，在云崩溃后形成的微行星中，铁 60 含量较低（通过其稳定的衰变产物镍 60 测量）。
The result is inconsistent with a supernova scenario, she said.
她说，这个结果与超新星的情况不一致。
The Vela Supernova Remnant formed after the explosion of a star in a supernova.
船帆座超新星遗迹是在超新星中恒星爆炸后形成的。
Alan Dyer/Stocktrek Images/Science Source
艾伦·戴尔/Stocktrek Images/Science Source
Researchers have come up with explanations for the missing iron.
研究人员已经对缺失的铁提出了解释。
“Meteoricists are famously argumentative folks,” wrote Alan Boss , an astronomer at Carnegie Science in Washington, D.C., in an email.
“流星学家是出了名的好争论的人，”华盛顿特区卡内基科学研究所的天文学家艾伦·博斯在一封电子邮件中写道。
“There always seems to be a counterexample to anything someone claims to be the case.”
“任何人声称的情况似乎总是有一个反例。”
For instance, the aluminum could have exploded out of the supernova, while the iron — coming from deeper in the star’s core — could have fallen back into the dead star.
例如，铝可能从超新星中爆炸出来，而来自恒星核心深处的铁可能会落回到死亡的恒星中。
Or the explosion could have come from a quirky supernova that didn’t generate iron-60 at all.
或者爆炸可能来自一颗根本不产生铁60的古怪超新星。
It could also be that iron-60 wasn’t distributed evenly in the cloud, which could mean measurements from individual meteorites aren’t giving us the full picture.
也可能是铁 60 没有均匀地分布在云中，这可能意味着对单个陨石的测量并不能为我们提供完整的情况。
Dwarkadas dismisses these explanations as “hand-waving” attempts to fine-tune the models to match the data rather than finding a more general solution.
德瓦卡达斯认为这些解释是“挥手”，试图微调模型以匹配数据，而不是寻找更通用的解决方案。
“Many people seem to accept the idea that it’s not a supernova,” he said.
“许多人似乎都接受这不是超新星的想法，”他说。
But if the solar system didn’t start with a supernova, where did it get all that aluminum?
但如果太阳系不是从超新星开始的，那么它从哪里得到那么多铝呢？
A possibility many researchers now favor is that the aluminum-26 was delivered on the winds of a Wolf-Rayet star.
许多研究人员现在支持的一种可能性是，铝-26 是通过沃尔夫-拉叶星的风传送的。
Compared to our sun, a Wolf-Rayet star is much shorter-lived, dozens of times larger, and thousands of times as luminous.
与我们的太阳相比，沃尔夫-拉叶星的寿命要短得多，体积要大几十倍，亮度却要高出数千倍。
A star becomes a Wolf-Rayet star when its outer hydrogen shell is stripped away, either by the gravitational attraction of another star or by the strength of its own solar winds.
当一颗恒星的氢壳层被另一颗恒星的引力或自身太阳风的强度剥离时，它就成为沃尔夫-拉叶星。
A Wolf-Rayet star’s exposed core can send out solar winds at speeds of up to 3,000 kilometers a second.
沃尔夫-拉叶星暴露的核心可以以每秒 3,000 公里的速度发出太阳风。
“It basically sweeps up the surrounding material like a snowplow,” Dwarkadas said.
“它基本上就像扫雪机一样扫除周围的物质，”德瓦卡达斯说。
That swept-up material forms a shell around the star that can be 100 light-years across.
这些被扫过的物质在恒星周围形成了一个直径可达 100 光年的外壳。
The shell, which creates a bubble around the Wolf-Rayet star, is tens of thousands of times denser than the surrounding interstellar medium.
壳层在沃尔夫-拉叶星周围形成了一个气泡，其密度是周围星际介质的数万倍。
The Dolphin Head Nebula is a Wolf-Rayet star surrounded by a bubble an estimated 60 light-years across.
海豚头星云是一颗沃尔夫拉叶星，周围环绕着一个直径约 60 光年的气泡。
Image processed by Sauro Gaudenzi, original data from Telescope Live.
图片由 Sauro Gaudenzi 处理，原始数据来自 Telescope Live。
The shell contains enough material to build a solar system.
外壳含有足够的材料来建造太阳系。
It should contain a lot of aluminum-26, and — crucially — it should contain very little iron-60.
它应该含有大量的铝 26，而且最重要的是，它应该含有很少的铁 60。
“I’m looking for a star that produces only aluminum-26,” Lugaro said.
“我正在寻找一颗只生产铝 26 的恒星，”卢加罗说。
“The place where we can make only aluminum-26 is in the winds of these very massive stars.”
“我们只能制造铝 26 的地方就在这些巨大恒星的风中。”
Astronomers have observed suns forming within the shells of Wolf-Rayet stars, Dwarkadas said.
德瓦卡达斯说，天文学家观察到太阳是在沃尔夫-拉叶星的壳内形成的。
By his estimate, as much as 16% of all sun-size stars in our galaxy could have formed this way.
根据他的估计，我们银河系中多达 16% 的太阳大小的恒星可能是以这种方式形成的。
“If it’s true, there’s no reason it should be true only for our solar system,” he said.
“如果这是真的，那么它没有理由只适用于我们的太阳系，”他说。
“Ours will not be unique.”
“我们的不会是独一无二的。”
Dwarkadas and his colleagues have laid out perhaps the most complete model for how the solar winds of a Wolf-Rayet star could have blasted aluminum-26 into our solar system as it formed.
德瓦卡达斯和他的同事们提出了也许是最完整的模型，说明沃尔夫-拉叶星的太阳风如何在铝 26 形成时将其吹入我们的太阳系。
Afterward, the Wolf-Rayet star, with a lifetime of only a few million years, would most likely have collapsed into a black hole, although evidence for this would be long gone, Dwarkadas said.
德瓦卡达斯说，此后，这颗寿命只有几百万年的沃尔夫-拉叶星很可能会坍缩成黑洞，尽管这方面的证据早已不复存在。
There are problems with the Wolf-Rayet idea, Lugaro said.
卢加罗说，沃尔夫-拉叶的想法存在问题。
For instance, a Wolf-Rayet star creates such an energetic environment that it should have torn our newly formed solar system apart.
例如，沃尔夫-拉叶星创造了如此高能的环境，它应该能够撕裂我们新形成的太阳系。
Boss still favors the theory that our cloud of dust was ignited by a supernova.
博斯仍然赞成我们的尘埃云是由超新星点燃的理论。
Lugaro does not.
卢加罗没有。
“At the moment, from the nuclear-physics point of view,” she said, “I favor the winds of the Wolf-Rayet stars.” However, she said, new information could change her mind next week.
“目前，从核物理学的角度来看，”她说，“我喜欢沃尔夫-拉叶星的风。”然而，她说，下周新的信息可能会改变她的想法。
“This is a problem that needs to be looked at from different angles.
“这是一个需要从不同角度看待的问题。
We are still fighting a bit about this.”
我们仍在为此争论不休。”
In Boston, Liu put the meteorite back in its safe.
在波士顿，刘将陨石放回保险箱。
On her computer, she opened a live view through the microscope of a nanoprobe that can measure the chemical composition of tiny pieces of material.
在她的电脑上，她通过纳米探针的显微镜打开了实时视图，该探针可以测量微小材料的化学成分。
She and other researchers are using the device to study bits of meteorite dissolved in acid, on the hunt for grains with the right chemical composition to have come from a Wolf-Rayet star.
她和其他研究人员正在使用该设备研究溶解在酸中的陨石碎片，寻找来自沃尔夫-拉叶星的具有正确化学成分的颗粒。
Liu operated the nanoprobe remotely (it was in Washington, D.C.), slowly scrutinizing the meteorite bits scattered across a field of gold foil.
刘远程操作纳米探测器（位于华盛顿特区），慢慢地仔细检查散布在一片金箔上的陨石碎片。
“This is like a fishing expedition,” Liu said.
“这就像一次钓鱼探险，”刘说。
Her next step, assuming she can find a good number of grains with the right chemical composition to have come from a Wolf-Rayet star, would be to measure whether they show signs of having been enriched in aluminum-26.
假设她能找到大量具有来自沃尔夫拉叶星的化学成分正确的颗粒，她的下一步将是测量它们是否显示出富含铝 26 的迹象。
This chemical information could then be used to constrain astrophysical models of the Wolf-Rayet scenario for the start of the solar system.
然后，这些化学信息可用于约束太阳系开始时的沃尔夫-拉叶情景的天体物理模型。
Liu acknowledged that the presence of such grains wouldn’t be a slam dunk for the Wolf-Rayet star theory; for instance, aluminum-enriched dust could have been produced by much older stars long before our solar system formed.
刘承认，这种颗粒的存在并不能满足沃尔夫-拉叶星理论的要求。例如，早在太阳系形成之前，富含铝的尘埃就可能是由更古老的恒星产生的。
But the absence of such grains would suggest that the Wolf-Rayet idea is off.
但如果没有这种颗粒，就表明沃尔夫-拉叶的想法是错误的。
She watched the nanoprobe at work, delving billions of years into the past.
她观察纳米探测器的工作，探究数十亿年前的过去。
Studying these grains, Liu said, gives her a new sense of the unique circumstances that led to the existence of our planet.
刘说，研究这些谷物让她对导致我们星球存在的独特环境有了新的认识。
“If you think about these radioactive isotopes — these rock-forming elements and life-forming elements,” she said, “when you know how they are produced in stars, you realize it is not so easy to get the right amount.
“如果你想想这些放射性同位素——这些岩石形成元素和生命形成元素，”她说，“当你知道它们是如何在恒星中产生时，你就会意识到获得适量的放射性同位素并不容易。
You have to form at the right time and place.”
你必须在正确的时间和地点组建。”
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