2026年5月4日 / 美国东部时间中午12:15 / 哥伦比亚广播公司/美联社
一项新研究表明，冥王星外一颗微小的冰封世界拥有一层稀薄而脆弱的大气层，其形成原因可能是火山喷发或彗星撞击。
日本国立天文台的首席研究员有本航平表示，这颗直径仅约300英里的“迷你冥王星”被认为是太阳系中迄今发现的、首个被明确探测到拥有引力束缚全球大气层的最小天体。
美国西南研究院的艾伦·斯特恩曾领导NASA“新视野号”冥王星及外太阳系探测任务，他并未参与此次研究，他说：“这是一项了不起的进展，但迫切需要独立验证。若得到证实，其意义将极为深远。”
若该发现得到确认，这颗天体将成为太阳系海王星轨道外第二个拥有大气层的天体——仅次于冥王星本身。
这一发现为研究太阳系最遥远、最寒冷的柯伊伯带天体提供了新视角。2024年，研究人员借助日本的三台望远镜，观测到这颗天体从一颗背景恒星前方经过，短暂遮挡了星光。
“这改变了我们对太阳系小天体的认知，不仅限于海王星之外的区域，”有本航平在一封电子邮件中说道。他补充道，在如此微小的天体周围发现大气层“着实令人意外”，并挑战了“大气层仅局限于大型行星、矮行星和部分大型卫星”的传统观点。
此图片由日本国立天文台提供，展示了海王星外天体(612533) 2002 XV93遮挡背景恒星的艺术想象图。
这颗被正式编号为(612533) 2002 XV93的小行星属于冥族小天体，其公转周期为海王星的三分之二，即海王星完成3次太阳轨道运行时，它已完成2次公转。在这项研究开展时，它距离地球超过34亿英里，甚至比拥有已观测到大气层的柯伊伯带唯一其他天体——冥王星——还要遥远。
根据周一发表在《自然·天文学》期刊上的研究，这颗冰封天体的大气层厚度仅为地球保护层的500万至1000万分之一。
甚至比冥王星稀薄的大气层还要稀薄50至100倍。有本航平表示，大气层中最有可能的化学成分是甲烷、氮气或一氧化碳，这三种气体中的任何一种都可以解释该天体从恒星前方经过时观测到的星光变暗现象。
有本航平指出，后续观测——尤其是借助NASA的韦伯太空望远镜——可以验证大气层的组成成分。
冰火山还是彗星碰撞？
研究人员无法确定大气层的确切成因，而且这层大气层远不足以支持生命存在。
但他们推测，大气层可能是由该天体内部通过冰火山喷发释放出的气体形成的。
也有可能是彗星撞击该天体时扬起的物质形成了大气层，若是如此，这层大气层将逐渐消散。
西班牙天文学家何塞·路易斯·奥尔蒂斯并未参与此项研究，他长期研究海王星外的矮行星，认为研究结果很有趣，但呼吁保持谨慎。
“我仍对大气层的存在表示怀疑，我们需要更多数据，”他告诉法新社。
奥尔蒂斯表示，对观测结果的另一种解释可能是，该天体周围存在贴近其本体的环系统。
有本航平承认，无法排除“大气层之外的其他非常规解释”。
但他补充道：“近乎侧视的环似乎与我们观测到的主要特征不符。”
两位天文学家都呼吁开展进一步观测，以深入了解这颗奇特的天体——尤其是借助詹姆斯·韦伯太空望远镜。
此前也有观点认为，体积略小于冥王星的矮行星鸟神星可能拥有极薄的大气层，但部分科学家对此持怀疑态度。冥王星曾长期被视为太阳系第九大行星，但在2006年，国际天文学联合会将其重新归类为矮行星。
上周，NASA局长贾里德·艾萨克曼暗示，该局正考虑将冥王星重新归类为完整的行星。
“我完全支持‘重新让冥王星成为行星’的立场，”艾萨克曼说道。
艾萨克曼是在支持一项将NASA科学预算削减一半的提案时发表上述言论的，这一言论激怒了部分天文学家。
“一边叫嚣‘重新让冥王星成为行星’，一边摧毁我们这些研究它的人的职业生涯，这太离谱了！”行星科学家阿迪恩·丹顿在Bluesky平台上写道。
法新社对本文亦有贡献。
Mysterious world beyond Pluto may have an atmosphere, astronomers say
May 4, 2026 / 12:15 PM EDT / CBS/AP
A new study suggests that a tiny, icy world beyond Pluto harbors a thin, delicate atmosphere that may have been created by volcanic eruptions or a comet strike.
Just 300 miles or so across, this mini Pluto is thought to be the solar system’s smallest object yet with a clearly detected global atmosphere bound by gravity, said lead researcher Ko Arimatsu of the National Astronomical Observatory of Japan.
“This is an amazing development, but it sorely needs independent verification. The implications are profound if verified,” said Southwest Research Institute’s Alan Stern, the lead scientist behind NASA’s New Horizons mission to Pluto and beyond. He was not involved in the study.
If confirmed, the rock would become just the second world past Neptune in our solar system to host an atmosphere — after only Pluto itself.
The finding offers fresh insight into our solar system’s farthest, coldest objects in a region known as the Kuiper Belt. Researchers used three telescopes in Japan to observe the object in 2024 as it passed in front of a background star, briefly dimming the starlight.
“It changes our view of small worlds in the solar system, not only beyond Neptune,” Arimatsu said in an email. Finding an atmosphere around such a small object was “genuinely surprising,” he added, and challenges “the conventional view that atmospheres are limited to large planets, dwarf planets and some large moons.”
This image provided by NAOJ shows artist’s impression of the trans-Neptunian object (612533) 2002 XV93 occulting a background star. Ko Arimatsu/AP
This so-called minor planet — formally known as (612533) 2002 XV93 — is considered a plutino, circling the sun twice in the time it takes Neptune to complete three solar orbits. At the time of the study, it was more than 3.4 billion miles away, farther than even Pluto, the only other object in the Kuiper Belt with an observed atmosphere.
This cosmic iceball’s atmosphere is believed to be 5 million to 10 million times thinner than Earth’s protective atmosphere, according to the study appearing Monday in the journal Nature Astronomy.
It’s 50 to 100 times thinner than even Pluto’s tenuous atmosphere. The likeliest atmospheric chemicals are methane, nitrogen or carbon monoxide, any of which could reproduce the observed dimming as the object passed before the star, according to Arimatsu.
Further observations, especially by NASA’s Webb Space Telescope, could verify the makeup of the atmosphere, according to Arimatsu.
Ice volcanoes or comet collision?
The researchers could not say for sure what created the atmosphere, which is nowhere near thick enough to support life.
But they suggested it could have been made by gas being shot out from the world’s interior by erupting ice volcanoes.
Or it could have been kicked up by a comet smashing into the world, which would mean it will gradually disappear.
Jose-Luis Ortiz, a Spanish astronomer not involved in the research who studies dwarf planets beyond Neptune, said the results were interesting, but urged caution.
“I still doubt that it is an atmosphere. We need more data,” he told AFP.
An alternative explanation for the observations could be that the object has a ring close to its body, Ortiz said.
Ko Arimatsu acknowledged that he could not rule out “exotic alternatives” to an atmosphere.
However, “a nearly edge-on ring does not seem consistent with the main features of our observations,” he added.
Both astronomers called for further observations to reveal more about this strange world — particularly with the James Webb space telescope.
There have also been suggestions that a dwarf planet called Makemake, which is slightly smaller than Pluto, could have a very thin atmosphere, though some scientists are skeptical. Pluto was long considered our ninth planet, but in 2006 the International Astronomical Union reclassified Pluto as a dwarf planet.
Last week, NASA administrator Jared Isaacman suggested the space agency was considering reinstating Pluto as a fully-fledged planet.
“I am very much in the camp of ‘make Pluto a planet again,’” Isaacman said.
Isaacman made the comments while endorsing a proposal to halve NASA’s science budget, riling some astronomers.
“It’s wild to ‘make Pluto a planet again’ while decimating the careers of those of us that study it!” planetary scientist Adeene Denton wrote on Bluesky.
Agence France-Presse contributed to this report.
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