67P is a Jupiter-family comet that orbits the Sun every ∼6.5 years. It has a bi-lobed shape consisting of a ∼3 km body and a ∼2 km head connected by a narrow neck (Sierks et al. 2015). One of the most significant findings by Rosetta is the intricate interplay between the cometary nucleus and its coma. The nucleus, being
Corresponding author: Xian Shi shi@shao.ac.cn 2 the source of gas and dust coma, is simultaneously being replenished and reshaped by coma materials (Thomas et al.

2015; Keller et al. 2017). The repository of pre- and post-perihelion imaging data have allowed us to investigate changes of the nucleus (Barrington et al. 2023), as well as their interrelation with cometary gas and dust activities (Hu et al. 2017a). Nominal dust and gas emission from the nucleus are predominately controlled by the diurnal cycle of solar irradiation as the nucleus rotates with a period of ∼12.4 h (De Sanctis et al. 2015). It forms the observable fine structures of the dust coma that are shaped by local topography and viewing conditions (Shi et al. 2018). Collimated dust features, or dust “jets”, were identified to originate from various morphological features, such as fractured terrains, scarps, pitted texture and also, smooth areas (Vincent et al. 2016a; Shi et al. 2016; Vincent et al. 2015; Fornasier et al. 2019). In contrast, spontaneous activities, or “outbursts”, are irregular and intense emanation events that could be triggered by different processes including thermal cracking, rupture of deep volatile reservoir, landslides, etc. as observations and models proposed (Skorov et al. 2016; Pajola et al. 2017; Agarwal et al. 2017; Vincent et al. 2016b). Dust activities play an important role in redistributing materials around the nucleus. Dust grains and aggregates lifted might not escape the nucleus’ gravity but rendezvous in the near-nucleus coma, with a considerable portion ultimately falling back (Thomas et al. 2015; Keller et al. 2017). Fine dust, with typical sizes of micro-meter to centimeter, can bury different surface features, especially small boulders and outcrops, while some previously covered surfaces can be exposed by dust removal (Hu et al. 2017a; Keller et al. 2017; El-Maarry et al. 2017; Cambianica et al. 2020). Decimeter- to meter-sized blocks released from the nucleus have also been observed in the near-nucleus coma, some of which with trajectories falling back towards the nucleus (Agarwal et al. 2017; Pfeifer et al. 2022; Shi et al. 2024). For larger chunks, several meters to tens of meters in size, their relocation usually creates more remarkable surface changes. Cliff collapse combined with outburst are found to predominantly contribute to the formation of talus, as the crumbling wall creates new boulders and debris fields (Pajola et al. 2017). A boulder with diameter of ∼10 m in the neck region could have dislodged from a nearby cliff and bounced several times across the surface, leaving trails in the smooth terrain (Vincent et al. 2019). Considering larger chunks can retain a considerable portion of volatile ices in the process of being redeposited, their migration contribute notably to the mass and volatile cycle of the comet (Keller et al. 2017). However, the driving mechanism and development process of such kind of boulder migration are still poorly understood. Especially, how such events are related to local activity, or what role the gas and dust activities play, need further investigation. The arguably most intriguing case of boulder migration is the transport of a ∼30-m-diameter boulder by ∼140 m, which is by far the largest boulder that is identified with displacement on 67P (Figure 1, El-Maarry et al. (2017)). The event took place in the Khonsu region of the southern hemisphere of 67P (Figure 1a, Thomas et al. (2018)). Khonsu is one of the most active regions on the nucleus, as numerous outbursts and morphological changes were observed (Hasselmann et al. 2019; Barrington et al. 2023). In this area the peak of surface changes and activities occurred one month after perihelion (2015 August 13, rh = 1.243AU) (Hasselmann et al. 2019). The migrated boulder was first reported by El-Maarry et al. (2017), who narrowed the time of the migration to between 2015 August 1 and October 30. Hasselmann et al. (2019) estimated the activity time to within two months after 67P’s perihelion (Figure 2). The triggering mechanism of such event 3 remains not well understood, while nominal water ice activity should not be sufficient to mobilize such massive boulder.