天文学家在太阳系外发现了一群岩石

Astronomers think they’ve found an entire population of asteroids originating from outside our solar system, according to a new paper.

根据一篇新论文，天文学家们认为他们已经发现了来自太阳系外的整个小行星群。

The objects at the centre of this investigation aren’t new discoveries. Called the Centaurs, they’re mysterious asteroids that orbit in the neighbourhood of Jupiter and beyond. These objects take highly inclined orbits relative to the plane of the rest of the planets, and in at least one case, orbit the “wrong” way relative to the rest of the solar system’s objects. By playing the laws of physics in reverse, scientists Fathi Namouni at the Université Côte d’Azur in France and Helena Morais at UNESP in Brazil found that 19 of these objects likely originated around another star.

这次调查的中心对象并不是新发现。它们被称为半人马座，是一种神秘的小行星，在木星附近或更远的地方运行。这些天体的轨道相对于其他行星的平面高度倾斜，至少在一种情况下，它们的轨道相对于太阳系其他天体的方向是“错误的”。法国科特迪瓦大学的科学家法特希·纳穆尼和巴西联合国环境规划署的海伦娜·莫莱斯发现，通过颠倒物理学定律，其中19个天体可能起源于另一颗恒星。

Astronomers first spotted the object (514107) 2015 BZ509, now called Ka‘epaoka‘awela, in the Pan-STARRS survey in 2015. Analysis of this asteroid revealed something shocking: It was orbiting the wrong way around the solar system in a stable yet eccentric orbit near Jupiter, on a tilt relative to the rest of the planets.

天文学家在2015年的Pan-STARRS调查中首次发现了该天体(514107)BZ509，现在被称为Ka 'epaoka 'awela。对这颗小行星的分析揭示了一件令人震惊的事情：它在木星附近以一种稳定但偏心的轨道绕太阳系运行，相对于其他行星呈倾斜状态。

Morais and Namouni studied that object’s orbit, built a simulation, and played in reverse the behaviour of a million imaginary objects that fit Ka‘epaoka‘awela’s orbital parameters, each with slightly different properties within the margin of error of the original observations. Most of the simulated objects either crashed into the Sun or other planets or were ejected from the solar system, but both of these cases failed to produce sensical origin stories for the asteroids once they turned the arrow of time back forward, Namouni explained. The ones that did obey the laws of physics were stable since the founding of the solar system 4.5 billion years ago. The researchers interpreted their observations as the objects having been captured from elsewhere.

莫赖斯(Morais)和纳莫尼(Namouni)研究了该物体的轨道，建立了一个模拟系统，并对符合Ka 'epaoka 'awela轨道参数的上百万个虚拟物体的行为进行了反向模拟，每个物体的属性在原始观测值的误差范围内略有不同。纳莫尼解释说，大多数模拟的物体要么撞向太阳或其他行星，要么被抛出太阳系，但这两种情况都没有产生关于小行星起源的耸人听闻的故事。那些遵守物理定律的行星自45亿年前太阳系建立以来一直很稳定。研究人员将他们的观察解释为这些物体是从其他地方捕获的。

While some scientists doubted that conclusion, given that other explanations hadn’t been fully ruled out, Namouni and Morais continued on their search. They ran similar reverse-time simulations for other Centaurs and some objects past Neptune, specifically those forming more than a 60-degree angle between the planetary plane and their orbit. For 19 of these objects, not only did the stable orbits remain at the end of the simulations, but they took on orientations relative to the planets that could not be explained if these objects were formed in our solar system. The pair concluded that they’d found an entire population of objects captured from outside the solar system and published their results this week in the Monthly Notices of the Royal Astronomical Society.

尽管一些科学家对这一结论表示怀疑，因为其他的解释还没有被完全排除，但Namouni和Morais仍在继续他们的研究。他们对其他人马和海王星附近的一些物体进行了类似的反向时间模拟，特别是那些在行星平面和轨道之间形成超过60度角的物体。对于其中的19个天体，不仅在模拟结束时它们的稳定轨道仍然存在，而且它们的方向与行星有关，如果这些天体是在我们的太阳系中形成的，这些行星的方向是无法解释的。他们得出的结论是，他们发现了太阳系外捕获的所有天体，并于本周在《皇家天文学会月刊》上发表了他们的研究结果。

Namouni told Gizmodo that, despite the initial push back, he hasn’t seen peer-reviewed papers contradicting their 2018 results. But it’s always possible that some other explanation could correctly fit the team’s newest set of calculations – an interstellar origin is just one potential way to explain the data that they see. On the flip side, this is just a study of outliers. Who knows if other rocks from outside the solar system are lurking among the more familiar entities? After all, we’ve recently been visited by two comets from outside the solar system, one of which didn’t look too different from comets that originate inside the solar system.

Namouni告诉Gizmodo，尽管最初遭到了反对，但他还没有看到同行评审的论文与2018年的结果相矛盾。但总有可能有其他的解释能够正确地符合该团队最新的计算结果——星际起源只是解释他们所看到的数据的一种可能的方式。另一方面，这只是对异常值的研究。谁知道其他来自太阳系外的岩石是否潜伏在我们更熟悉的实体中呢?毕竟，最近有两颗来自太阳系外的彗星造访过我们，其中一颗看起来与来自太阳系内部的彗星并无太大不同。

Interstellar objects stably orbiting inside of our own solar system would be an exciting find, of course. And if these Centaurs truly are from another star, then astronomers could learn about the composition of those distant systems by studying the Centaurs more closely – or maybe one day paying them a visit.

当然，稳定地在太阳系内绕轨道运行的星际物体将是一个令人兴奋的发现。如果这些半人马确实来自另一颗恒星，那么天文学家可以通过更仔细地研究这些人头马来了解这些遥远星系的组成——或者有一天拜访他们。