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JWST finds Earth-like planets can form in harsh galactic environments
Despite being blasted by molecule-destroying ultraviolet radiation, at least one planet-forming disk in the Lobster Nebula has the building blocks of rocky planets.
The Lobster Nebula, also known as NGC 6357, is teeming with massive stars that have carved and sculpted the nebula’s wisps of gas and dust. Located around 5,500 light-years from Earth in the constellation Scorpius, the nebula is one of the youngest and closest massive star-forming regions. It famously contains some of the most massive stars in the Milky Way Galaxy, nestled within a cluster dubbed Pismis 24.
New observations from the James Webb Space Telescope (JWST) focus on one of Pismis 24’s residents, a young Sun-like star swathed in a dusty protoplanetary disk from which planets may eventually form. This particular star sits near a pair of massive, bright stars that blast the region with ultraviolet (UV) radiation, a common occurrence in massive clusters.
The work was published Nov. 30 in The Astrophysical Journal Letters. It is the first time the effects of external radiation on protoplanetary disks has been studied in massive star-forming regions. Despite the punishing and chaotic environment, researchers found that the inner regions of this particular disk, dubbed XUE 1, don’t seem that different from the disks around stars in calmer, lower-mass star-forming regions. The similarity indicates that rocky planets can form even in challenging surroundings. The find can now give further clues into the types of environments in which rocky planets can form.
“This result is unexpected and exciting! It shows that there are favorable conditions to form Earth-like planets and the ingredients for life even in the harshest environments in our galaxy,” said María Claudia Ramírez-Tannus, the study’s first author and an astronomer at the Max Planck Institute for Astronomy in Germany.
Analyzing more disks
JWST’s powerful Mid-Infrared Instrument allows scientists to peer into the inner regions of XUE 1 and catalog the molecules and environmental conditions there. Because UV radiation can break molecules apart, researchers weren’t sure whether the building blocks of rocky planets could survive. But MIRI observations detected water, carbon monoxide, carbon dioxide, acetylene, hydrogen cyanide, and crystalline silicate dust in XUE 1. Not only was it the first time such molecules had been seen in conditions like those in the star cluster, but crystalline silicate dust in particular is a fundamental necessity for forming rocky, Earth-like worlds.
The observations are part of JWST’s eXtreme UItraviolet Environments (XUE) program, which studies planet-forming disks in massive star-forming regions. JWST actually observed 15 protoplanetary disks in the Lobster Nebula. “If intense radiation hampers the conditions for planet formation in the inner regions of protoplanetary disks, NGC 6357 is where we should see the effect”, said study co-author Arjan Bik at Stockholm University.
Astrophysicists will continue to study the other disks to look for evidence of water and other essential planetary building blocks. They aren’t yet sure whether XUE 1 is a commonplace example or a rare fluke. The team also wants to explore whether terrestrial planet formation is more common in more or less massive star-forming regions.
“XUE 1 shows us that the conditions to form rocky planets are there, so the next step is to check how common that is,’ said Ramírez-Tannus. “We will observe other disks in the same region to determine the frequency with which these conditions can be observed.”
注释：
teem: v
表示" 充满；富于；把……倒空；倾泻"，means "have in great numbers"，如：The river teems with all kinds of fish in summer. 夏天这条河里各种各样的鱼多得很。
Scorpius: n
表示" 天蝎座"，means "a large zodiacal constellation between Libra and Sagittarius"，如：The constellations Sagittarius and Scorpius lie in this direction as well. 人马座和天蝎座也在这个位置。
dub: v
表示"起绰号，授予称号"，means " give a nickname to sb"，如：The papers dubbed them The Fab Four'. 报刊给他们起了个绰号叫｀四绝＇.
swathe: v
表示" 缠裹；紧绑"，means "=swath; wrap in swaddling clothes"，如：His head was swathed in bandages. 他的头用绷带缠着。
protoplanetary: adj
表示" 原始行星的"，如：Disks have also been observed around many young stars; astronomers often call them protoplanetary disks because they appear to be similar to the one that must have formed our own solar system. 许多年轻恒星的周遭也可发现圆盘的踪影；天文学家通常称它们为原生行星盘，因它们看来与太阳系所赖以成形的那个圆盘类似。
Astrophysical: adj
表示"天体物理学的"，means "of or concerned with astrophysics"，如：The findings will appear in the Astrophysical Journal Letters. 这一发现将会发表在天体物理学的日志中。
acetylene: n
表示" [化]乙炔；电石气"，means "a colorless flammable gas used chiefly in welding and in organic synthesis"，如：These gauges are designed for measuring the pressure of medium acetylene. 该压力表适用于测量乙炔介质的压力。
cyanide: n
表示" 氰化物"，means "an extremely poisonous salt of hydrocyanic acid"，如：Cyanide is used to kill insects. 氰化物可用来杀害虫。
fluke: n
表示" 侥幸；"，means "a stroke of luck"，如：His failure in history examination was a mere fluke. 他历史考试没能及格纯属偶然。
terrestrial: adj
表示"陆地的；陆生的；地球的"，means "of or relating to or inhabiting the land as opposed to the sea or air"，如：Men live on the terrestrial parts of the earth. 人们住在地球上的陆地部分。
中文简要说明：
德国天文学家又惊又喜！韦伯太空望远镜（JWST）发现类地行星在极为苛刻的星系环境中形成，那里无时无刻都存在着能够破坏分子结构的超强紫外线辐射轰击，研究发现龙虾星云（Lobster Nebula）中至少存在一个足以形成行星的盘状结构，并且拥有岩石行星的基本组成成分，这项研究目前已经发表在《天体物理学期刊》（The Astrophysical Journal Letters）上。
据《天文学》（Astronomy）报导，NGC 6357又名龙虾星云，充满了受到大质量恒星影响的星云气体和尘埃细丝。这个星云位于天蝎座，距离地球约5500光年，里头有许多大质量恒星而且他们靠得很近，其中包含一个十分著名的「疏散星团」Pismis 24，有许多大质量的恒星挤在一起嵌套在Pismis 24当中。
可想而知，一大堆恒星靠在一起的地方，各种辐射都是毁灭性的，然而韦伯太空望远镜（JWST）的最新观测发现Pismis 24当中存在一颗年轻、类似太阳的恒星被尘土飞扬的原行星盘（Protoplanetary Disc）所包裹，而行星正式从原行星盘当中所诞生的，而这颗恒星被夹在2颗大质量、明亮的恒星附近，这颗恒星向该区域轰炸的毁灭性的紫外线辐射。
尽管环境严酷且混乱，研究人员发现这个原行星盘（命名为XUE 1）的内部区域似乎与较为平静、质量较低的星形成区域中的恒星盘没有太大区别。这种相似性表明，即使在具有挑战性的环境中，岩石行星仍然能够形成。
这是首次研究外部辐射对大质量星形成区域中，原行星盘的影响。这一发现现在可以进一步提供有关岩石行星形成环境类型的线索。
研究的第一作者、德国马克斯普朗克研究院（MPI）天文学研究所的天文学家克劳迪娅（María Claudia Ramírez-Tannus）在新闻稿中表示：「这个结果出乎意料且令人兴奋！它显示出在我们银河系最严酷的环境中，形成类似地球的行星和生命的基本成分的有利条件仍然存在。」
由于紫外线辐射可以将分子分解，研究人员不确定岩石行星的基本组成成分是否能够存活。但红外线仪器观测到了XUE 1中仍然富含水、一氧化碳、二氧化碳、乙炔、氢氰酸和结晶硅酸尘（crystalline silicate）。这是目前首次在类似恒星团中的条件下被观测到，而且特别是结晶硅酸尘对于形成岩石状、类地行星是一种基本要件。
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