Scientists find remains of cannibalized baby planets in Jupiter's cloud-covered belly
科学家在木星云层之下发现其吞噬的星子遗骸
Jupiter's innards are full of the remains of baby planets that the gas giant gobbled up as it expanded to become the behemoth we see today, scientists have found. The findings come from the first clear view of the chemistry beneath the planet's cloudy outer atmosphere.
科学家发现，木星内部充满了星子残骸。这颗气体巨星正是通过吞噬这些星子，才膨胀成如今的庞然大物。这一发现来自于对这颗行星浑浊的外层大气下化学物质的首次清晰观察。
Despite being the largest planet in the solar system, Jupiter has divulged very little about its inner workings. Telescopes have captured thousands of images of the swirling vortex clouds in the gas giant's upper atmosphere, but these Van Gogh-esque storms also act as a barrier blocking our view of what's below.
尽管木星是太阳系中最大的行星，但人们对其内部运作却知之甚少。望远镜已经捕捉到了这颗气态巨星高层大气中旋转不停的涡旋云的数千张图像，但这些梵高式的风暴也相当于屏障，阻挡人们对其下面的世界一探究竟。
"Jupiter was one of the first planets to form," in the first few million years when the solar system was taking shape around 4.5 billion years ago, lead researcher Yamila Miguel, an astrophysicist at Leiden University in The Netherlands, told Live Science. However, we know almost nothing for certain about how it formed, she added.
荷兰莱顿大学的天体物理学家、首席研究员亚米拉·米格尔（Yamila Miguel）告诉《生活科学》(Live Science)，大约在45亿年前，太阳系开始成型。在那之后的几百万年里，“木星是最早形成的行星之一”。然而，我们几乎不知道它是如何形成的，她补充说。
Related: Jupiter is a whirling world in stunning (and woozy) footage from Juno spacecraft
相关：在朱诺号宇宙飞船的令人惊艳（和眩晕）镜头中，木星是一个旋转不停的世界。
In the new study, researchers were finally able to peer past Jupiter's obscuring cloud cover using gravitational data collected by NASA's Juno space probe. This data enabled the team to map out the rocky material at the core of the giant planet, which revealed a surprisingly high abundance of heavy elements. The chemical make-up suggests Jupiter devoured baby planets, or planetesimals, to fuel its expansive growth.
在这项新的研究中，研究人员终于能够利用美国宇航局朱诺太空探测器收集的引力数据窥视木星模糊云层之下的景象。这些数据使研究小组能够绘制出这颗巨型行星核心的岩石物质。结果表明，木星核心存在大量重元素。其化学成分表明，木星曾吞噬星子（planetesimals），以促进其膨胀增长。
Jupiter may predominantly be a ball of swirling gas today, but it started its life by accreting rocky material — just like every other planet in the solar system. As the planet's gravity pulled in more and more rocks, the rocky core became so dense that it started attracting large amounts of gas from far distances — predominantly hydrogen and helium left over from the sun's birth — to form its enormous gas-filled atmosphere.
虽然木星现今主要由旋转气体组成，但就像太阳系中的其他行星一样，其生命是通过吸积岩石物质开始的。随着木星的引力吸引越来越多的岩石，岩石核心变得非常密集，开始从远处吸引大量气体（主要是太阳诞生时遗留下来的氢和氦）从而形成巨大的充满气体的大气层。
There are two competing theories about how Jupiter managed to collect its initial rocky material. One theory is that Jupiter accumulated billions of smaller space rocks, which astronomers nickname pebbles (although these rocks are likely closer in size to boulders rather than actual pebbles).
关于木星如何收集其最初的岩石物质，存在两种相互竞争的理论。一种理论是木星积累了数十亿块较小的太空岩石，天文学家称之为鹅卵石（尽管这些岩石的大小可能更接近巨石，而不是真正的鹅卵石）。
The opposing theory, which is supported by the findings from the new study, is that Jupiter's core was formed from the absorption of many planetesimals — large space rocks spanning several miles, which if left undisturbed could have potentially acted as seeds from which smaller rocky planets like Earth or Mars could develop.
新研究发现支持的相反理论则称，木星的核心是通过吸收大量星子形成的。这些星子是长达几英里的大型太空岩石，如果不受干扰，它们可能会逐渐成长为地球或火星等较小岩石行星。
However, until now it has not been possible to definitively say which of these theories is correct. "Because we cannot directly observe how Jupiter was formed we have to put the pieces together with the information we have today," Miguel said. "And this is not an easy task."
然而，到目前为止，还不能确切地说这些理论中哪一个是正确的。“因为我们不能直接观察木星是如何形成的，所以我们必须凭借我们今天掌握的信息一点点拼凑，进行综合研判，”米格尔说。“这不是一件容易的事情。”
To try to settle the debate, researchers needed to build a picture of Jupiter's insides. "Here on Earth, we use seismographs to study the interior of the planet using earthquakes," Miguel said. But Jupiter has no surface to put such devices onto, and Jupiter's core is unlikely to have much tectonic activity anyway, she added.
为了解决这一争论，研究人员需要绘制木星内部的图像。“在地球上，我们使用地震仪通过地震来研究地球内部，”米格尔说。但她补充说，木星没有表面可以放置这样的设备，木星的核心也不太可能有太多的构造活动。
Instead, the researchers built computer models of Jupiter's innards by combining data, which was predominantly collected by Juno, as well as some data from its predecessor Galileo. The probes measured the planet's gravitational field at different points around its orbit. The data showed that rocky material accreted by Jupiter has a high concentration of heavy elements, which form dense solids and, therefore, have a stronger gravitational effect than the gaseous atmosphere. This data enabled the team to map out slight variations in the planet's gravity, which helped them to see where the rocky material is located within the planet.
与地球研究方法不同的是，研究人员通过结合主要由朱诺号收集的数据以及它的前身伽利略号收集的一些数据，建立了木星内部构造的计算机模型。探测器测量了木星轨道周围不同点的引力场。数据显示，木星吸积的岩石物质含有高浓度的重元素，形成致密的固体，因此比气态大气具有更强的引力作用。这些数据使研究小组能够绘制出木星引力的微小变化，这有助于他们测定岩石物质在木星中的位置。
"Juno provided very accurate gravity data that helped us to constrain the distribution of the material in Jupiter's interior," Miguel said. "It is very unique data that we can only get with a spacecraft orbiting around the planet."
“朱诺号提供了非常准确的重力数据，帮助我们推测木星内部物质的分布情况，”米格尔说。“这种数据非常独特，只能通过环绕木星轨道的航天器获得。”
The researcher's models revealed that there is an equivalent of between 11 and 30 Earth masses of heavy elements within Jupiter (3% to 9% of Jupiter's mass), which is much more than expected.
研究人员的模型显示，木星内部的重元素相当于11到30个地球质量（木星质量的3%到9%)，这比预期的要多得多。
The new models point to a planetesimal-gobbling origin for Jupiter because the pebble-accretion theory cannot explain such a high concentration of heavy elements, Miguel said. If Jupiter had initially formed from pebbles, the eventual onset of the gas accretion process, once the planet was large enough, would have immediately ended the rocky accretion stage. This is because the growing layer of gas would have created a pressure barrier that stopped additional pebbles from being pulled inside the planet, Miguel explained. This curtailed rocky accretion phase would likely have given Jupiter a greatly reduced heavy metal abundance, or metallicity, than what the researchers calculated.
米格尔说，新的模型指向木星的星子吞噬起源，因为卵石吸积理论无法解释如此高浓度的重元素。如果木星最初是由吸收岩石形成的，一旦其体积足够大，木星就会停止吸积岩石，转而开始吸收气体。米格尔解释说，这是因为不断增长的气体层会产生一个压力屏障，阻止更多的岩石被拉入行星内部。若岩石吸积阶段因此缩短，木星的金属含量应该大量减少，比研究人员计算的要低。
However, planetesimals could have glommed onto Jupiter's core even after the gas accretion phase had begun; that's because the gravitational pull on the rocks would have been greater than the pressure exerted by the gas. This simultaneous accretion of rocky material and gas proposed by the planetesimal theory is the only explanation for the high levels of heavy elements within Jupiter, the researchers said.
然而，即使在气体吸积阶段开始后，星子也可能在木星的核心聚集；这是因为对岩石的引力会大于气体施加的压力。研究人员说，星子理论提出的岩石物质和气体的同时吸积是木星内重元素含量高的唯一解释。
The study also revealed another interesting finding: Jupiter's insides do not mix well into its upper atmosphere, which goes against what scientists had previously expected. The new model of Jupiter's insides shows that the heavy elements the planet has absorbed have remained largely close to its core and the lower atmosphere. Researchers had assumed that convection mixed up Jupiter's atmosphere, so that hotter gas near the planet's core would rise to the outer atmosphere before cooling and falling back down; if this were the case, the heavy elements would be more evenly mixed throughout the atmosphere.
这项研究还揭示了另一个有趣的发现：木星的内部不能很好地与高层大气混合，这与科学家此前的预期相反。全新木星内部模型显示，这颗行星吸收的重元素在很大程度上保持在靠近其核心和低层大气的地方。研究人员曾假设对流混合了木星的大气，因此行星核心附近较热的气体会在冷却和回落之前上升到外部大气；如果是这样的话，重元素会在整个大气中更加均匀地混合。
However, it is possible that certain regions of Jupiter may have a small convection effect, and more research is needed to determine exactly what is going on inside the gas giant's atmosphere, Miguel said.
然而，米格尔说，木星的某些区域可能有存在小规模对流效应，需要更多的研究来确定这个气体巨星的大气中到底发生了什么。
The researchers' findings could also change the origin stories for other planets in the solar system. "Jupiter was the most influential planet in the formation of the solar system," Miguel said. Its gravitational pull helped to shape the size and orbits of its cosmic neighbors, and so determining how it came to be has important knock-on effects for other planets, she added. The findings also suggest a potential planetesimal origin for the other gas giants in the solar system: Saturn, Uranus and Neptune.
研究人员的发现也可能改变太阳系其他行星的起源故事。“木星是太阳系形成过程中影响最大的行星，”米格尔说。她补充说，它的引力帮助塑造了周边行星的大小和轨道，因此确定木星的起源对其他行星有重要的连锁效应。这些研究发现还表明，太阳系中其他气体巨星（土星、天王星和海王星）也可能起源于星子吸积。
Other gaseous worlds in other star systems might also have formed by gobbling up planetesimals rather than pebbles, which means they may also have higher metallicity than their appearance would suggest. It is, therefore, important that when we find these new worlds, which are being searched for using NASA's James Webb Telescope, we don't judge them by their cloudy covers, the researchers said.
其他恒星系统中的其他气态行星也可能是通过吞食星子而不是岩石形成的，这意味着它们的金属含量可能比看上去更高。因此，重要的是，当我们发现这些新世界时（美国航空航天局的詹姆斯·韦伯望远镜正在对其进行搜索），不要根据它们多云的外表来进行判断，研究人员说。
The study was published online June 8 in the journal Astronomy and Astrophysics (opens in new tab).
这项研究于6月8日在线发表于《天文学和天体物理学》杂志（在新标签中打开）。
Originally published on Live Science.
最初发表于《生活科学》。
