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冥王星之外的寒冷区域里，可能藏着一颗此前没人注意到的矮行星。这篇文章介绍鲁宾天文台的新发现：一个暂名 2026 ED138 的大型冰质天体。文章先说明发现本身，再讲天文学家如何用搜索程序从海量数据中找出它，又如何反复核查、找到多年前的旧图像；接着解释它为什么一直被银河附近密集的星光“藏”了起来；最后说明为什么仅凭大小还不能确认它就是矮行星。阅读时可留意 may、could、expected 等词如何表达尚未确认的结论，以及 however、still、by comparison 等词如何引出转折和比较。

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Our solar system may have a new member. On 27 October, scientists at the Vera C. Rubin Observatory in Chile announced that they had found a large, icy object far beyond Pluto. For now, it is called 2026 ED138, and it could become only the sixth known dwarf planet, joining Pluto, Ceres, Eris, Haumea and Makemake.

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我们的太阳系可能迎来了一位新成员。10 月 27 日，位于智利的薇拉·C·鲁宾天文台的科学家宣布，他们在冥王星以外很远的地方发现了一个巨大的冰质天体。它目前被称为 2026 ED138，有可能成为已知的第六颗矮行星，与冥王星、谷神星、阋神星、妊神星和鸟神星并列。

The object was found by Matthew Holman, an astronomer at the Center for Astrophysics, Harvard & Smithsonian. On the evening of 13 October, he was running data collected by Rubin earlier this year through a search program he had built with his colleague Kevin Napier. The program compares billions of tiny points of light and looks for ones that belong to the same moving object. When Holman saw how bright and distant this one was, he realised that it was likely to be unusually large.

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这个天体是由哈佛-史密森天体物理中心的天文学家马修·霍尔曼发现的。10 月 13 日晚上，他正用自己与同事凯文·内皮尔共同编写的搜索程序处理鲁宾天文台今年早些时候收集的数据。该程序会比对数十亿个微小光点，寻找属于同一个移动天体的那些光点。霍尔曼看到这个天体如此明亮又如此遥远时，意识到它很可能异常巨大。

“My first reaction was one of excited disbelief,” Holman said. Because objects like this are very rare, he first checked whether he or the program had made a mistake. Mario Jurić of the University of Washington then searched Rubin’s records and found more sightings. In total, Rubin had seen the object 30 times on 20 nights between March and July. Older pictures from another camera in Chile showed it as far back as 2016, giving the team more than ten years of its path.

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“我的第一反应是兴奋又难以置信，”霍尔曼说。由于这样的天体非常罕见，他首先检查了是不是自己或程序出了错。随后，华盛顿大学的马里奥·尤里奇在鲁宾天文台的记录中搜索，找到了更多观测记录。总计来看，鲁宾天文台在 3 月至 7 月间的 20 个夜晚共观测到这个天体 30 次。智利另一台相机拍摄的更早图像显示，它最早可追溯到 2016 年，使研究团队掌握了其十多年的运行轨迹。

The object is now about 46 times as far from the Sun as Earth is. Pluto, by comparison, has an average distance of about 40 times. Its path is also tilted by about 25 degrees from the flat plane in which most planets move.

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这个天体目前与太阳的距离约为地球与太阳距离的 46 倍。相比之下，冥王星的平均距离约为 40 倍。它的轨道还与大多数行星运行的平面倾斜约 25 度。

So why was something so big missed for so long? It sits in a part of the night sky close to the Milky Way, where millions of stars crowd together. Earlier surveys often avoided this busy area or looked at it only briefly. Rubin, which has the largest camera ever built for astronomy, takes repeated pictures of the whole southern sky, so it can notice a slow-moving point among all those stars.

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那么，这么大的天体为什么这么久都没被发现？它位于夜空中靠近银河的区域，那里有数以百万计的恒星密集分布。早期的巡天观测常常避开这片繁忙的区域，或者只是短暂地观测过。鲁宾天文台拥有有史以来为天文学建造的最大相机，会反复拍摄整个南天，因此能在众多恒星中注意到一个缓慢移动的光点。

Size alone, however, does not make a dwarf planet. An object must have enough mass for its own gravity to pull it into a round shape. Based on its brightness and distance, the team thinks 2026 ED138 is between 600 and 1,500 kilometres wide, and icy bodies that large are expected to be round. Still, the scientists say more observations, such as measurements in infrared light, are needed to learn its exact size before it can be confirmed.

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不过，仅凭大小并不能成为矮行星。一个天体必须有足够的质量，使自身引力把它拉成球形。根据它的亮度和距离，研究团队认为 2026 ED138 的直径在 600 到 1500 公里之间，而这么大的冰质天体预计是圆的。尽管如此，科学家表示，还需要更多观测，例如红外波段的测量，来确定它的确切大小，之后才能确认它的身份。

新闻来源

• Rubin Observatory · NSF–DOE Vera C. Rubin Observatory Reveals Its First Dwarf Planet Candidate in Our Solar System (27 Oct 2026)
• NSF · New dwarf planet candidate discovered by NSF–DOE Rubin Observatory (27 Oct 2026)
• UW News · Rubin Observatory reveals its first dwarf planet candidate in our solar system (27 Oct 2026)
• Scientific American · Astronomers may have just discovered our solar system’s sixth dwarf planet (27 Oct 2026)

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