分类： 天文学 >> 天文学 提交时间： 2023-02-19
Thomas S. Statler
Sabina D. Raducan
Olivier S. Barnouin
Mallory E. DeCoster
Steven R. Chesley
Brent Barbee
Harrison F. Agrusa
Saverio Cambioni
Andrew F. Cheng
Elisabetta Dotto
Siegfried Eggl
Eugene G. Fahnestock
Fabio Ferrari
Dawn Graninger
Alain Herique
Isabel Herreros
Masatoshi Hirabayashi
Stavro Ivanovski
Martin Jutzi
Özgür Karatekin
摘要： NASA's Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology. Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later Hera mission, will result in measurement of the momentum transfer efficiency accurate to ~10% and characterization of the Didymos binary system. But DART is a single experiment; how could these results be used in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos's response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge of the physical properties of asteroidal materials and predictive power of impact simulations; what information about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection mission should be informed by this understanding. We generalize the momentum enhancement factor $\beta$, showing that a particular direction-specific $\beta$ will be directly determined by the DART results, and that a related direction-specific $\beta$ is a figure of merit for a kinetic impact mission. The DART $\beta$ determination constrains the ejecta momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos's near-surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered asteroid will require Earth-based observations and benefit from in-situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian-Yang Li
Masatoshi Hirabayashi
Tony L. Farnham
Jessica M. Sunshine
Matthew M. Knight
Gonzalo Tancredi
Fernando Moreno
Brian Murphy
Cyrielle Opitom
Steve Chesley
Daniel J. Scheeres
Cristina A. Thomas
Eugene G. Fahnestock
Andrew F. Cheng
Linda Dressel
Carolyn M. Ernst
Fabio Ferrari
Alan Fitzsimmons
Simone Ieva
Stavro L. Ivanovski
摘要： Some active asteroids have been proposed to be the result of impact events. Because active asteroids are generally discovered serendipitously only after their tail formation, the process of the impact ejecta evolving into a tail has never been directly observed. NASA's Double Asteroid Redirection Test (DART) mission, apart from having successfully changed the orbital period of Dimorphos, demonstrated the activation process of an asteroid from an impact under precisely known impact conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope (HST) from impact time T+15 minutes to T+18.5 days at spatial resolutions of ~2.1 km per pixel. Our observations reveal a complex evolution of ejecta, which is first dominated by the gravitational interaction between the Didymos binary system and the ejected dust and later by solar radiation pressure. The lowest-speed ejecta dispersed via a sustained tail that displayed a consistent morphology with previously observed asteroid tails thought to be produced by impact. The ejecta evolution following DART's controlled impact experiment thus provides a framework for understanding the fundamental mechanisms acting on asteroids disrupted by natural impact.
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