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Internal Affairs of Small Primitive Asteroids: Thermo-Physical Evolution Context for Carbonaceous and Volatile-Rich Bodies

Gal Sarid
Delivered As: 
Abstract Text: 

The OSIRIX-REx (NASA, 101955 Bennu) and Hayabusa 2 (JAXA, 162173 Ryugu) missions are set to explore fairly small, porous and primitive near-Earth asteroids (C and B type). In addition, there is much interest now in exploration concepts of Mars' moons, Phobos and Deimos, which are very similar to C/D-type asteroids. Such bodies should contain organic compounds, hydrated minerals and perhaps volatile material. Thus, it is of great interest to decipher their internal structure and composition, how they evolved and how representative are the surfaces of the bulk interiors.

For this we need to understand the physical conditions driving chemical evolution of water and organic-rich material through a porous medium, as main-belt asteroids of various sizes could have incorporated water ice upon formation. Indeed, the meteoritic record reveals such evidence, in the form of hydrated minerals, mostly in the CI, CM and CR carbonaceous chondrites, which also indicate that more complex physical-chemical interactions must have happened early on and set the compositions and lithologies we observe today. The precursor bodies may have also undergone early evolution and internal processing of mineral and organic reservoirs. If conditions are met and sustained, exothermic reactions can contribute greatly to the overall heating balance and compositional variation.

Our thermal evolution code can deal with mixtures of water, silicate minerals and organic compounds, with relevant transitions and interactions, as a function of the thermodynamic variables. We will utilize the robustness of the code to examine different origin and early evolution scenarios, such as parent-body evolution, increased collision input early on, orbital evolution at further/closer perihelia, varied initial composition and buried reservoirs of volatile compounds. We further examine the boundary conditions in surface and near-surface layers, by calculating heat transfer effects in granular material, including conduction, radiation and advection between particles and pores. The granular material can further react to vapor flows and small impacts, effectively changing the diffusivity and conductivity of surface layers. We will present preliminary integrative models for internal evolution, from formation to current state, as a reactive rock- water-organic porous system.

Tim J. Stubbs
SSERVI Identifier: 

Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."