Department of Physics and Astronomy, The University of Western Ontario, London, Ontario N6A 3K7, Canada.
Centre for Planetary Science and Exploration (CPSX), London, Ontario N6A 3K7, Canada.
Nature. 2017 Mar 29;543(7647):687-689. doi: 10.1038/nature22029.
Recent theoretical work in celestial mechanics has revealed that an asteroid may orbit stably in the same region as a planet, despite revolving around the Sun in the sense opposite to that of the planet itself. Asteroid 2015 BZ was discovered in 2015, but with too much uncertainty in its measured orbit to establish whether it was such a retrograde co-orbital body. Here we report observations and analysis that demonstrates that asteroid 2015 BZ is indeed a retrograde co-orbital asteroid of the planet Jupiter. We find that 2015 BZ has long-term stability, having been in its current, resonant state for around a million years. This is long enough to preclude precise calculation of the time or mechanism of its injection to its present state, but it may be a Halley-family comet that entered the resonance through an interaction with Saturn. Retrograde co-orbital asteroids of Jupiter and other planets may be more common than previously expected.
近年来，天体力学的理论研究表明，小行星可能在与行星相同的区域稳定地围绕太阳运行，尽管它的旋转方向与行星本身相反。小行星 2015 BZ 于 2015 年被发现，但由于其轨道测量存在太多不确定性，无法确定它是否是逆行共轨天体。在这里，我们报告了观测和分析结果，证明小行星 2015 BZ 确实是木星的逆行共轨小行星。我们发现，2015 BZ 具有长期稳定性，在当前的共振状态已经存在了大约一百万年。这足以排除对其进入当前状态的时间或机制进行精确计算的可能性，但它可能是一颗哈雷型彗星，通过与土星的相互作用进入了共振状态。木星和其他行星的逆行共轨小行星可能比之前预期的更为常见。
