Planets, like those in our solar system, form in a bottom-up process where small bits of rock and ice clump together and grow larger over time. But the heftier the planet, the harder it is to explain its formation that way.
行星，就像我们太阳系中的行星一样，是在自下而上的过程中形成的，其中小块的岩石和冰聚集在一起，并随着时间的推移变得越来越大。但行星越重，就越难用这种方式解释它的形成。
Astronomers used NASA’s James Webb Space Telescope to examine 29 Cygni b, an object about 15 times as massive as Jupiter orbiting a nearby star. They found multiple lines of evidence that 29 Cygni b indeed formed from this bottom-up process, bringing new insights into how the heftiest planets come to be. A paper describing these findings published Tuesday in The Astrophysical Journal Letters .
天文学家使用 NASA 的詹姆斯·韦伯太空望远镜观测了天鹅座 29 b，这是一个质量约为木星 15 倍、围绕附近恒星运行的天体。他们发现了多项证据，证明天鹅座 29 b 确实是通过这种自下而上的过程形成的，这为了解最重行星的形成过程带来了新的见解。周二在《天体物理学杂志快报》上发表的一篇描述这些发现的论文。
The planet formation process is broadly understood to occur within gigantic disks of gas and dust around stars through a process called accretion. Dust gloms together into pebbles, which collide and grow larger and larger, forming protoplanets and eventually planets. The largest then collect gas to become giants like Jupiter. Since it takes more time for gas giants to form, and the disk of planet-forming material eventually evaporates and disappears, planetary systems end up with many more small planets than large planets.
人们广泛认为，行星的形成过程是通过称为吸积的过程发生在恒星周围巨大的气体和尘埃盘内。尘埃聚集成卵石，它们相互碰撞并变得越来越大，形成原行星，最终形成行星。最大的行星随后会收集气体，成为像木星一样的巨型行星。由于气态巨行星的形成需要更多的时间，并且形成行星的物质盘最终会蒸发和消失，因此行星系统最终会出现比大行星更多的小行星。
In contrast, stars form when a vast cloud of gas fragments and each piece collapses under its own gravity, growing smaller and denser. A similar fragmentation process could theoretically occur within protoplanetary disks as well. That could explain why some very massive objects are found billions of miles from their host stars, in regions where the protoplanetary disk should have been too tenuous for accretion to occur.
相比之下，当巨大的气体云破裂并且每一块在自身重力作用下塌陷、变得更小、密度更大时，恒星就形成了。理论上，类似的碎片过程也可能发生在原行星盘内。这可以解释为什么一些非常大的天体被发现距离它们的主恒星数十亿英里，而这些区域的原行星盘本应太脆弱而无法发生吸积。
29 Cygni b sits on the dividing line between what can be explained by these two different mechanisms. It weighs 15 times Jupiter and orbits its star at an average distance of 1.5 billion miles (2.4 billion kilometers), about the same as Uranus in our solar system. The research team targeted it because it could potentially result from either process.
29 Cygni b 位于这两种不同机制所能解释的分界线上。它的重量是木星的 15 倍，绕恒星运行的平均距离为 15 亿英里（24 亿公里），大约与太阳系中的天王星相同。研究小组瞄准它是因为它可能是由任一过程产生的。
“In computer models, it’s very easy for fragmentation in a disk to run away to much higher masses than 29 Cygni b. This is the lowest mass you could plausibly get. But at the same time, it’s about the highest mass you could get from accretion,” said lead author William Balmer of the Johns Hopkins University and the Space Telescope Science Institute, both in Baltimore.
“在计算机模型中，磁盘中的碎片很容易逃逸到比 29 Cygni b 高得多的质量。这是你可能获得的最低质量。但与此同时，这大约是你可以从吸积中获得的最高质量，”主要作者、约翰·霍普金斯大学和太空望远镜科学研究所（均位于巴尔的摩）的威廉·巴尔默（William Balmer）说。
Balmer’s observing program used Webb’s NIRCam (Near-Infrared Camera) in its coronagraphic mode to directly image 29 Cygni b. This planet was the first of four objects targeted by the program, all of which are known to weigh between 1 and 15 times as much as Jupiter. The team also required their targets to orbit within about 9 billion miles (15 billion kilometers) of their stars.
巴尔默的观测计划使用韦伯的 NIRCam（近红外相机）在日冕模式下直接对天鹅座 29 b 进行成像。这颗行星是该计划瞄准的四个天体中的第一个，已知所有这些天体的重量都是木星的 1 到 15 倍。该团队还要求他们的目标在距恒星约 90 亿英里（150 亿公里）的范围内运行。
The planets were all young and still hot from their formation, ranging in temperature from about 1,000 to 1,900 degrees Fahrenheit (530 to 1,000 degrees Celsius). This would ensure their atmospheric chemistry was similar to the planets of HR 8799, whose system Balmer studied previously .
这些行星都很年轻，在形成时仍然很热，温度范围约为 1,000 至 1,900 华氏度（530 至 1,000 摄氏度）。这将确保它们的大气化学成分与巴尔默之前研究过的 HR 8799 的行星相似。
By choosing appropriate filters, the team was able to look for signs of light being absorbed by carbon dioxide (CO 2 ) and carbon monoxide (CO), which allowed them to determine the amount of those heavier chemical elements, which astronomers collectively call metals.
通过选择合适的滤光片，研究小组能够寻找二氧化碳 (CO 2 ) 和一氧化碳 (CO) 吸收光的迹象，从而确定这些较重化学元素（天文学家统称为金属）的含量。
They found strong evidence that 29 Cygni b is enriched in metals relative to its host star, which is similar to our Sun in its composition. Given the planet’s mass, the amount of heavy elements it contains is equivalent to about 150 Earths. This suggests that it accreted large amounts of metal-enriched solids from a protoplanetary disk.
他们发现了强有力的证据，表明天鹅座 29 b 相对于其宿主恒星富含金属，其成分与太阳相似。考虑到该行星的质量，其所含重元素的数量相当于大约 150 个地球。这表明它从原行星盘吸积了大量富含金属的固体。
The team also used a ground-based optical telescope array called CHARA (Center for High Angular Resolution Astronomy) to determine if the planet’s orbit is aligned with the spin of the star. They confirmed that alignment, which would be expected for an object that formed from a protoplanetary disk.
该团队还使用了名为CHARA（高角分辨率天文学中心）的地面光学望远镜阵列来确定行星的轨道是否与恒星的自转对齐。他们证实了这种排列，这对于由原行星盘形成的物体来说是预期的。
“We were able to update the planet’s orbit, and also observed the host star to determine its orientation with respect to that orbit,” said Ash Messier, co-author and a graduate student at Johns Hopkins University. “We showed that the inclination of the planet is well-aligned with the spin axis of the star, which is similar to what we see for the planets of our solar system.”
“我们能够更新行星的轨道，并观察主星以确定其相对于该轨道的方向，”合著者、约翰·霍普金斯大学的研究生阿什·梅西耶（Ash Messier）说。 “我们发现行星的倾角与恒星的自转轴完全一致，这与我们在太阳系行星上看到的类似。”
“Put together, this evidence strongly suggests that 29 Cygni b formed within a protoplanetary disk through rapid accretion of metal-rich material, rather than through gas fragmentation,” said Balmer. “In other words, it formed like a planet and not like a star.”
巴尔默说：“总而言之，这些证据有力地表明，天鹅座 29 b 是通过富含金属物质的快速吸积而在原行星盘内形成的，而不是通过气体碎裂形成的。” “换句话来说，它的形成像一颗行星，而不是像一颗恒星。”
As the team gathers data on the other three targets within their program, they plan to look for evidence of compositional differences between the lower-mass and higher-mass planets. This should provide additional insights into their formation mechanisms.
当团队收集计划中其他三个目标的数据时，他们计划寻找较低质量和较高质量行星之间成分差异的证据。这应该可以提供对其形成机制的更多见解。
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
詹姆斯·韦伯太空望远镜是世界上首屈一指的太空科学天文台。韦伯正在解开太阳系中的谜团，展望其他恒星周围的遥远世界，并探索宇宙的神秘结构和起源以及我们在其中的位置。韦伯是由 NASA 及其合作伙伴 ESA（欧洲航天局）和 CSA（加拿大航天局）领导的一项国际计划。
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Watch: Roman Space Telescope Coronagraph Animation
观看：罗马太空望远镜日冕仪动画