Testing the asteroid Pallas as the parent body of the active NEA Phaethon

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Protoplanets are fascinating bodies that provide a special sort of examples of geological processes observed on planets, e.g., volcanism, tectonics, and differentiation, yet in a special setting of sub-1000 km bodies that did not develop to full planets. Observations suggest that (2) Pallas fills a gap between (1) Ceres and (4) Vesta. Protoplanets Ceres and Vesta explored by the Dawn mission have comparable geology given similar surface gravities. While Vesta is much denser due to its anhydrous composition than the water-rich Ceres, Pallas is also denser, but it is unclear if due to an initially smaller water content, or water loss. Pallas offers a case study for a new and much more complete understanding of this class of objects which are very different from typical small asteroids, are precursors of planets, and have undergone planetary processes. Importantly, it is the suggested parent body of the near-Earth asteroid (3200) Phaethon that will be investigated by the Destiny+ mission. Focusing on Pallas, the proposed project targets to complete five science objectives focused on density, composition, structure, and chronology. A. Derive the accretion time of Pallas from its bulk density and a CM-like surface composition by modelling the evolution of the porosity and deriving a match between the calculated final bulk density and that of Pallas. B. Determine which internal composition and structure are consistent with a hydrated (sub-) surface, e.g., if the hydrated surface implies a high ice fraction in the mantle and crust, by calculating the evolution of the temperature and porosity and deriving the strength and composition of the material. C. Constrain the evolution of geodetic properties of Pallas, e.g., MOI coefficient and spin velocity, for the parameters constrained in A. and B. D. Determine if an object with Phaethon´s physical properties can be produced from Pallas for the assumption that Phaethon is a single fragment of its parent asteroid by comparing Phaethon´s physical properties with those obtained for Pallas. E. Determine if the thermal evolution of Pallas is compatible with the thermo-chronological record of CM, CY, or Tagish Lake chondrites, i.e., if Pallas can be the parent body of either of these groups, by fitting the thermal evolution calculated to the data available for these meteorite groups. The project aims to closing the gap between Ceres and Vesta in our understanding of protoplanets, to investigating if Pallas can be the parent asteroid of Phaeton, and to supporting the Destiny+ space mission with modeling studies.