Speaker
Description
On April 13, 2029, asteroid (99942) Apophis will pass within 32,000 km of Earth, offering a unique opportunity to study how Earth’s tidal forces affect asteroids, particularly those with complex internal structures. This study investigates possible mass shifts and structural changes within Apophis during its close encounter, focusing on the implications of its bilobed shape, resembling a contact binary. To do this analysis we employ Contact Dynamics (CD) granular mechanics simulations using the LMGC90 software to model Apophis as a multi-body system. CD methods are well-suited for modeling the interaction between strong components of a micro-gravity rubble pile body, as it does not allow for interpenetration or distortion of the individual grains, as opposed to Soft Sphere Discrete Element Methods (SSDEM). Also, CD allows for the use of polyhedron bodies for the individual grains, allowing for shape effects and complex geometries naturally. In our study we focus on the neck region between the two lobes, which will be the point of maximum stress when Apophis has its close Earth approach. We survey a range of different morphologies for the main components of Apophis and interstitial boulders, using both spherical particles and polyhedral particles. Our simulations are focused on the 12-hour flyby period when all of the Earth interactions occur, exploring the effects of orientation, friction, and cohesion. Our preliminary results show that the spherical models exhibit larger mass shifts, with the internal cores able to shift up to 1° when Apophis’s long axis was offset from Earth, rather than directly aligned. The polyhedral models tend to exhibit smaller mass shifts, with relative angle changes between the two lobes at least an order of magnitude less. We also observed minor boulder displacements in the neck region, typically on the order of centimeters, with occasional displacements exceeding 1 meter. These results suggest that Apophis’s neck is sensitive to tidal forces and will experience surface shifts during the flyby. This study highlights the need for in-situ observations to confirm the surface and internal changes predicted during the Apophis flyby. It also provides specific target regions where observations should be concentrated.