近日，香港大学Man Hoi Lee团队研究了一颗与白矮星在紧密双星系统中的逆行行星。2025年5月21日出版的《自然》发表了这项成果。

近距离伴星预计会通过潮汐截断原行星盘、阻碍星子的相互吸积和缩小动态稳定区域，对星周（S型）行星的形成和轨道稳定性产生不利影响。这解释了在紧密的双星系统中观察到的S型行星的缺乏。ν Octantis，其恒星成分的平均间距为2.6 AU，长期以来一直被怀疑在恒星之间的逆行且异常宽的轨道上拥有一颗环绕主行星。然而，反对其形成的强有力的理论依据和缺乏观测先例，对地球的现实构成了挑战。

研究组提出了新的径向速度测量结果，巩固了行星假说。对所有径向速度数据的稳定拟合要求行星轨道是逆行的，并且实际上是共面的。他们还报告了自适应光学成像的关键发现，即伴星是一颗白矮星。研究组对可靠的原始双星轨道设置的探索表明，恒星之间的最小间距为1.3 AU，与当前的行星轨道重叠，几乎无法想象环绕主行星轨道与年轻恒星同期形成的任何情况。这颗逆行行星一定起源于绕双星轨道或第二代原行星盘，表明了双星演化在行星系统形成和演化中的作用。

附：英文原文

Title: A retrograde planet in a tight binary star system with a white dwarf

Author: Cheng, Ho Wan, Trifonov, Trifon, Lee, Man Hoi, Cantalloube, Faustine, Reffert, Sabine, Ramm, David, Quirrenbach, Andreas

Issue&Volume: 2025-05-21

Abstract: Close-in companion stars are expected to adversely influence the formation and orbital stability of circumstellar (S-type) planets by tidally truncating protoplanetary discs1,2,3,4, impeding mutual accretion of planetesimals5,6,7,8 and narrowing dynamically stable regions9. This explains the observed dearth of S-type planets in tight binary star systems10,11,12,13. ν Octantis, whose stellar components have a mean separation of 2.6AU, has long been suspected of hosting a circum-primary planet in a retrograde and exceptionally wide orbit that resides midway between the stars14,15,16,17,18,19,20. Strong theoretical grounds against its formation and the absence of observational precedents, however, have challenged the reality of the planet. Here we present new radial velocity measurements that consolidate the planet hypothesis. Stable fits to all radial velocity data require the planetary orbit to be retrograde and practically coplanar. We also report the critical discovery from adaptive optics imaging that the companion star is a white dwarf. Our exploration of credible primordial binary orbital settings shows that the minimum separation between the stars was 1.3AU initially, which overlaps the current planetary orbit and makes any scenarios in which the circum-primary planetary orbit formed coevally with the young stars hardly conceivable. The retrograde planet must have originated from a circumbinary orbit or a second-generation protoplanetary disc, showing the role of binary stellar evolution in the formation and evolution of planetary systems.

DOI: 10.1038/s41586-025-09006-x

Source: https://www.nature.com/articles/s41586-025-09006-x