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“Self-Gravitating Small Bodies’ Shape Irregularity Influences Their Interiors and Dynamics”

by

Masatoshi Hirabayashi
Assistant Professor in Aerospace Engineering with an adjunct appointment in Geosciences | Auburn University.

Monday, February 20
2 pm - 3 pm 
Weber Lecture Hall 2

About the Seminar: 
Asteroids and comets are small self-gravitating objects targeted by planetary missions aiming for sample return, planetary deflection, and in-situ resource utilization. Their shapes are commonly irregular, though how such shapes contribute to their evolution is not well quantified. The author has built continuum mechanics techniques for quantifying how a small body’s irregular shape influences its interior and dynamics. His models quantified this correlation, having played central roles in providing measurable parameters to infer its evolution mechanism. Earlier, his continuum mechanics approach found that the spin period and bulk density controlled the shape evolution of a top-shaped asteroid like Ryugu and Bennu. This interpretation was widely accepted based on the geological/geophysical features observed by JAXA/Hayabusa2 and NASA/OSIRIS-REx, the recent asteroid sample return missions. Work has further been extended to use Finite Element Modeling approaches to show (i) substantial variations in the mutual dynamics within a binary system, described as the full two-body problem, under reshaping mechanisms and solar radiation (widely known as binary YORP, or bYORP) and (ii) high contrasts of the dynamics of deformable self-gravitating objects to those of rigid bodies under planetary tides. These predictions are testable by incorporating observations by NASA/DART, the planetary defense mission, and other ongoing/future planetary missions. This seminar will summarize the author’s modeling and planetary mission efforts in characterizing how self-gravitating small bodies’ shape irregularity influences their interiors and dynamics.

About the Speaker: 
Masatoshi Hirabayashi (Ph.D.) is an assistant professor in Aerospace Engineering with an adjunct appointment in Geosciences at Auburn University. He graduated from Aerospace Engineering Sciences at the University of Colorado Boulder and joined a research group in the Department of Earth, Atmospheric, and Planetary Science at Purdue University. His expertise is in Astrodynamics and Planetary Science, particularly in exploring complex dynamics phenomena and planetary surface evolutions. He was involved in a series of planetary missions, including JAXA/IKAROS (solar sail mission), JAXA/Hayabusa 1 and 2 (small body sample return mission), NASA/OSIRIS-REx (small body sample return mission), and ESA/JAXA/Bepi-Colombo (Mercury orbiter mission). Currently, he serves as Co-Is of NASA/DART (planetary defense mission) and NASA/VIPER (lunar rover mission). He also leads Hayabusa 2# as a Science Integration Lead. 11471 Toshihirabayashi is named after him for his contribution to small-body research.