冥王星之外 太阳系可能真的存在第九颗行星

There might be a ninth planet in the solar system after all, and it is not Pluto.

太阳系或许还是拥有第九颗行星，不是冥王星。

Two astronomers reported on Wednesday that they had compelling signs of something bigger and farther away — something that would satisfy the current definition of a planet, where Pluto falls short.

两名天文学家于周三通报，他们发现了令人信服的迹象，表明存在一颗更大、更遥远的天体——该星体将满足目前对行星的定义，而冥王星则不符合。

“We are pretty sure there’s one out there,” said Michael E. Brown, a professor of planetary astronomy at the California Institute of Technology.

“我们相当确定有那么一颗行星，”加州理工学院(California Institute of Technology)的行星天文学教授迈克尔·E·布朗(Michael E. Brown)说。

What Dr. Brown and a fellow Caltech professor, Konstantin Batygin, have not done is actually find that planet, so it would be premature to start revising mnemonics of the planets.

布朗博士和他的同事康斯坦丁·巴蒂金(Konstantin Batygin)尚未真正找到那颗行星，所以现在修改行星名单还为时过早。

In a paper published in The Astronomical Journal, Dr. Brown and Dr. Batygin lay out a detailed circumstantial argument for the planet’s existence in what astronomers have observed — a half-dozen small bodies in distant elliptical orbits.

布朗和巴蒂金在《天文学杂志》(The Astronomical Journal)上联合发表了一篇论文，提出详细的旁证，认为天文学家们观测到的现象——在遥远的椭圆轨道上运行的六个小天体——证明了这颗行星的存在。

What is striking, the scientists said, is that the orbits of all six loop outward in the same quadrant of the solar system and are tilted at about the same angle. The odds of that happening by chance are about 1 in 14,000, Dr. Batygin said.

这两位科学家称，一个突出的现象是，这六个天体的轨道全部位于太阳系的同一象限内，并且倾斜角度大致一样。巴蒂金表示，这种情况纯属巧合的概率大约是1.4万分之一。

A ninth planet could be gravitationally herding them into these orbits.

可能有第九颗行星通过引力将这些天体拉入这样的轨道。

For the calculations to work, the planet would be at least an equal to Earth, and most likely much bigger — perhaps a mini-Neptune with a mass about 10 times that of Earth. That would be 4,500 times the mass of Pluto.

要想理论成立，这颗行星至少要和地球尺寸相当，很可能要大得多——大概相当于一颗小海王星，质量是地球的10倍、冥王星的4500倍。

Pluto, at its most distant, is 4.6 billion miles from the sun. The potential ninth planet, at its closest, would be about 20 billion miles away; at its farthest, it could be 100 billion miles away. One trip around the sun would take 10,000 to 20,000 years.

冥王星运行到远日点时，距离太阳46亿英里。这颗有望成为第九大行星的天体距离太阳最近时是200亿英里，最远时可能是1000亿英里。绕行太阳一周需要1万到2万年。

“We have pretty good constraints on its orbit,” Dr. Brown said. “What we don’t know is where it is in its orbit, which is too bad.”

“我们对它的轨道参数有了不少了解，”布朗说。“我们尚不知道的是它在轨道上的位置，这太糟糕了。”

Alessandro Morbidelli of the d’Azur Observatory in France, an expert in dynamics of the solar system, said he was convinced. “I think the chase is now on to find this planet,” he said.

法国蔚蓝海岸天文台( d’Azur Observatory)的太阳系动力学专家亚历山德罗·莫比德利(Alessandro Morbidelli)觉得可信。“我认为现在的目标是找到这颗行星，”他说。

This would be the second time that Dr. Brown has upended the map of the solar system. In January 2005, he discovered a Pluto-size object, now known as Eris, in the Kuiper belt, the ring of icy debris beyond Neptune.

如若证实，这将是布朗第二次颠覆太阳系的图谱。2005年1月，他发现了一颗大小相当于冥王星的天体，位于海王星以外的充满冰结碎块的柯伊伯带(Kuiper Belt)。它如今命名为阋神星(Eris)。

The next year, the International Astronomical Union placed Pluto in a new category, “dwarf planet,” because in its view, a full-fledged planet must be the gravitational bully of its orbit, and Pluto was not.

第二年，国际天文学联合会(International Astronomical Union)就把冥王星归入名为“矮行星”的一个新类别，因为在该学会看来，一颗名副其实的行星必须能够清空轨道上的其他天体，而冥王星做不到这一点。

The first indication of a hidden planet beyond Pluto had come a couple of years earlier. The Kuiper belt extends outward from Neptune’s orbit, about 2.8 billion miles from the sun, to a bit less than twice Neptune’s orbit, about five billion miles.

在此之前两年，科学家就首次发现了冥王星以外可能存在隐藏行星的迹象。柯伊伯带从海王星的轨道向外延伸，一直到接近海王星轨道两倍的地方，也就是分布在距离太阳约28亿英里到50亿英里处。

Astronomers expected that beyond lay mostly empty space.

天文学家认为，那以外应当几乎空无一物。

Thus they were surprised when Dr. Brown and two colleagues spotted a 600-mile-wide icy world at a distance of eight billion miles that remained well outside the Kuiper belt even at the closest point in its orbit.

所以，当布朗和他的两名同事在80亿英里远的地方发现了一片直径600英里的冰雪世界时，科学家们颇为意外。就连该天体运行轨道的近日点也在柯伊伯带以外。

No one could convincingly explain how the object, which Dr. Brown named Sedna, got there, and the hope was that the discovery of more Sedna-like worlds would provide enlightening clues.

布朗把它命名为赛德娜(Sedna)。没有人能够对这颗天体为何出现在那里作出令人信服的解释。科学家希望，将来发现更多的类似天体，从而提供能带来启发的线索。

Instead, astronomers looked and found nothing, deepening the mystery.

但事与愿违，天文学家的搜寻一无所获，让此事变得更加扑朔迷离。

Finally, in 2014, Chadwick Trujillo, who had worked with Dr. Brown on the Sedna discovery, and Scott S. Sheppard, an astronomer at the Carnegie Institution for Science in Washington, reported a smaller object in a Sedna-like orbit, always remaining beyond the Kuiper belt.

最后，2014年，曾和布朗共同发现赛德娜的查德威克·特鲁希略(Chadwick Trujillo)与位于华盛顿的卡内基科学研究所(Carnegie Institution for Science)的天文学家斯科特·S·谢泼德(Scott S. Sheppard)通报，发现了一颗较小的天体有着与赛德娜类似的轨道，一直运行在柯伊伯带以外。

Dr. Trujillo and Dr. Sheppard noted that several Kuiper belt objects had similar orbital characteristics, and they laid out the possibility of a planet disturbing the orbits of these objects. “It was the best explanation we could come up with,” Dr. Trujillo said.

特鲁希略和谢泼德注意到，柯伊伯带的几个天体有类似的轨道特征。他们提出了一种假设：有可能存在一颗行星，正是它影响了这些天体的轨道。“这是我们能想到的最佳解释了，”特鲁希略博士说。

But the particulars of their proposed planet did not explain what was in the sky, Dr. Brown said.

不过，布朗称，他们提出的这颗行星的参数却无法解释太空中的现象。

“The theorists didn’t really take it seriously,” he said. “They figured it was all some observational effect. The observers didn’t take it seriously, because they figured it was all some theoretical thing they couldn’t understand.”

“理论领域的学者没当回事，”他说。“他们认为这都是某种观测效应。观测领域的学者也没当回事，因为他们认为这都是他们无法理解的某种理论。”

Still, the peculiarities of the orbits appeared genuine.

然而，它们轨道的特殊性看来是真实的。

Dr. Brown said he and Dr. Batygin “sat down and beat our heads against the wall for the last two years.”

布朗表示，他和巴蒂金“过去两年坐在那里，想破了脑袋。”

First, they focused on the six objects in stable orbits and disregarded others that had been recently flung out by Neptune.

他们开始把重点放在处于稳定轨道的六个小型星体上，不再考虑近期被海王星抛出的其他天体。

That made the picture clearer.

局面豁然开朗。

“They all point into the same overall direction,” Dr. Batygin said. “This is in stark contrast with the rest of the Kuiper belt.”

“他们都指向大致一样的方向，”巴蒂金说。“这和柯伊伯带的其他天体截然不同。”

Besides the long odds of this alignment being coincidental, Dr. Batygin said, this pattern would disperse over time.

且不说这种一致性纯属巧合的几率有多小，巴蒂金表示，这样的运行模式也本应随时间的流逝而消散。

That argued for the force of some unseen body guiding Sedna and the others.

他们认为，这是未曾发现的星体在吸引赛德娜和其他天体。

Dr. Batygin, a theorist, tried placing a planet among them, which scattered some Kuiper belt objects, but the orbits were not sufficiently eccentric.

作为理论天文学家，巴蒂金试图将一颗行星安放其中。这打散了柯伊伯带中的不少天体，但形成的椭圆轨道的离心率依然不够大。

Then he examined what would happen if a ninth planet were looping outward in the opposite direction. That, Dr. Batygin said, gave “a beautiful match to the real data.”

随后，他假设有第九大行星在相反方向向外绕行。巴蒂金表示，结果呈现出“与真实数据完美的匹配”。

The computer simulations showed that the planet swept up the Kuiper belt objects and placed them only temporarily in the elliptical orbits. Come back in half a billion years, Dr. Brown said, and Sedna will be back in the Kuiper belt, while other Kuiper belt objects will have been pushed into elliptical orbits.

计算机模拟显示，该行星将柯伊伯带的天体全部重新洗牌，只是暂时被安置在椭圆形轨道中。巴蒂金表示，五亿年后赛德娜会回到柯伊伯带，而其他天体也会被推入椭圆形轨道中。

Another strange result in the simulations: A few Kuiper belt objects were knocked into orbits perpendicular to those of the planets. Dr. Brown remembered that five objects had been found in perpendicular orbits.

模拟中另一奇怪的结果是：小部分柯伊伯带天体被撞向了与其他行星相垂直的轨道。根据巴蒂金回忆，在垂直轨道中发现了五个天体。

“They’re exactly where we predicted them to be,” he said. “That’s when my jaw hit my floor. I think this is actually right.”

“它们完全处在我们预测的位置上，”他称，“我惊得下巴都掉地了。我认为这应该是对的。”

Dr. Morbidelli said a possible ninth planet could be the core of a gas giant that started forming during the infancy of the solar system; a close pass to Jupiter could have ejected it. Back then, the sun resided in a dense cluster of stars, and the gravitational jostling could have prevented the planet from escaping to interstellar space.

莫比德利表示，可能存在的第九大行星，也许是一个气态巨行星的核心，自太阳系初期就开始形成；可能当它经过木星时被引力抛远了。当时的太阳处在密集的恒星群中，而引力的推挤可能阻止了这颗行星逃到星际空间。

“I think they’re onto something real,” he said. “I would bet money. I would bet 10,000 bucks.”

“我觉得他们这样下去有戏，”他说，“我敢打赌。我赌一万块。”

Dr. Brown said he began searching for the planet a year ago, and he thought he would be able to find it within five years. Other astronomers will most likely also scan that swath of the night sky.

巴蒂金称，他早在一年前就开始寻找这颗行星，他认为自己可以在五年内找到它。其他天文学家很有可能也会去搜索那一片夜空。

If the planet exists, it would easily meet the definition of planet, Dr. Brown said.

他说如果这颗行星真的存在，它应该能轻易吻合对行星的定义。

“There are some truly dominant bodies in the solar system and they are pushing around everything else,” Dr. Brown said. “This is what we mean when we say planet.”

“在太阳系有一些格外显要的星体，它们会肆意摆布其他一切天体，”巴蒂金说，“这就是我们说的‘行星’的意思。”