Tidal resurfacing model for (99942) Apophis during the 2029 close approach with Earth

We numerically investigate tidally induced surface refreshing on Apophis during its close approach with Earth within a perigee distance of 5.96 Earth radii on 2029 April 13. We implement a tidal resurfacing model with two stages: dynamics modelling of the entire body to determine time-varying accelerations and surface slope profiles felt by each surface patch during the 6-h-long closest encounter, and discrete-element method modelling to track motions of surface grains in localized patches. The surface slope profiles and measured grain motions are combined to statistically extrapolate the 'expected' percentage of resurfaced area. Using the tidal resurfacing model, we present surface maps showing the total expected resurfacing on Apophis given three representative encounter orientations. Our simulation results indicate that tidal resurfacing, limited to certain localized regions, will likely occur half an hour before perigee and on the scale of 1 per cent of Apophis's entire surface area. Our models indicate that the most likely locations to detect tidal resurfacing are: initially high-sloped regions (>30 degrees) regardless of the encounter orientation of Apophis, and mid-sloped regions (15 degrees-30 degrees) that experience a significant positive slope variation (>0.5 degrees), which is mainly controlled by the encounter orientation. Expected data from ground-based observations of the 2029 flyby will help us better constrain the targeted locations likely to experience tidal resurfacing. We thus expect to find evidence supporting tidal resurfacing via further analysis of post-encounter surface images or albedo changes at the expected resurfaced areas.

Automated summary

In this study, we numerically investigate the tidal resurfacing phenomenon on Apophis during its close approach with Earth in 2029. By implementing a two-stage tidal resurfacing model, we predict the surface slope profiles and grain motions during the closest encounter and statistically extrapolate the expected resurfaced area. Our simulation results indicate that tidal resurfacing will occur half an hour before perigee and cover approximately 1% of Apophis's surface. We identify the most likely locations to detect tidal resurfacing based on the surface slope profiles and encounter orientation.