Most co-orbital objects in the Solar system are thought to follow tadpole-type orbits, behaving as Trojans. However, most of Earth's identified co-orbitals are moving along horseshoe-type orbits. The current tally of minor bodies considered to be Earth co-orbitals amounts to 18; of them, 12 are horseshoes, five are quasi-satellites, and one is a Trojan. The semimajor axis values of all these bodies librate between $0.983$ au and $1.017$ au. In this work, we have studied the dynamical behaviour of objects following orbits with semimajor axis within this range that may be in a 1:1 mean-motion resonance with Earth. Our results show that asteroids 2016 CO$_{246}$, 2017 SL$_{16}$, and 2017 XQ$_{60}$ are moving along asymmetrical horseshoe-type orbits; the asteroid 2018 PN$_{22}$ follows a nearly symmetric or regular horseshoe-type orbit. Asteroids 2016 CO$_{246}$, 2017 SL$_{16}$, and 2017 XQ$_{60}$ can remain in the horseshoe co-orbital state for about $900$ yr, $3300$ yr and $2700$ yr, respectively. Asteroid 2018 PN$_{22}$ has a more chaotic dynamical behaviour; it may not stay in a horseshoe co-orbital state for more than 200 yr. The horseshoe libration periods of 2016 CO$_{246}$, 2017 SL$_{16}$, 2017 XQ$_{60}$, and 2018 PN$_{22}$ are 280, 255, 411, and 125 yr, respectively.

中文翻译：

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地球的马蹄形轨道：当前人口和新候选者

太阳系中的大多数共轨天体被认为遵循蝌蚪型轨道，表现为特洛伊木马。然而，地球上大多数已确定的共同轨道都在沿着马蹄形轨道运动。目前被认为是地球共同轨道的小天体总数为 18 个；其中，马蹄铁12颗，准卫星5颗，木马1颗。所有这些天体的长半轴值在 $0.983$au 和 $1.017$au 之间波动。在这项工作中，我们研究了物体沿着半长轴在这个范围内的轨道运动的动力学行为，这些轨道可能与地球发生 1:1 的平均运动共振。我们的结果表明，小行星 2016 CO$_{246}$、2017 SL$_{16}$ 和 2017 XQ$_{60}$ 正在沿着不对称的马蹄形轨道运动；小行星 2018 PN$_{22}$ 遵循几乎对称或规则的马蹄形轨道。小行星 2016 CO$_{246}$、2017 SL$_{16}$ 和 2017 XQ$_{60}$ 可以以每年约 900 美元、每年 3300 美元和每年 2700 美元的价格保持在马蹄形共轨状态， 分别。小行星 2018 PN$_{22}$ 的动力学行为更加混乱；它可能不会停留在马蹄形共轨状态超过 200 年。2016年CO$_{246}$、2017年SL$_{16}$、2017年XQ$_{60}$和2018年PN$_{22}$的马蹄形平衡期分别为280、255、411和125年，分别。