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SCIENTIA SINICA Physica, Mechanica & Astronomica, Volume 49, Issue 8: 084502(2019) https://doi.org/10.1360/SSPMA2018-00352

Physical properties and structural evolution of asteroids

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  • ReceivedOct 12, 2018
  • AcceptedDec 19, 2018
  • PublishedApr 23, 2019
PACS numbers

Abstract

Asteroids are thought to harbor an abundance of valuable mineral resources, and the original materials that were present in the early solar system. The information contained in these small bodies could provide us with critical clues about how the planets formed as well as life started on the Earth. With the help of observations and the data returned by several successful asteroid missions, the progression of asteroid research has been expanded from understanding the asteroids’ orbits, shapes, rotation states and spectral classes to exploring more details about their internal structures and how they evolve in response to external effects. Among all the possible forms of asteroids’ structures, the rubble-pile structure provides an interesting insight about how asteroids’ structures evolve and a reasonable explanation for some observations. However, the discrete and low-strength characteristics of this structure raise many open questions to understanding its evolution, identifying its physical properties, and designing future asteroid missions. Based on the orbital distribution and the observed physical properties of asteroids, this study attempts to draw a whole picture on how asteroids’ structure evolves and demonstrates the reasons why most asteroids above 300 m size scale should possess rubble-pile structures. From the perspective of the physics of granular mechanics, a review of progress in investigating the structural characteristics and the dynamical evolution mechanisms of rubble-pile asteroids is present. A thorough comparative analysis on the efforts made by different methods shows that, theoretical analyses and laboratory experiments suffer from the limitation of applications and high economic cost, respectively, while numerical modeling techniques can efficiently serve many purposes. Among all the numerical methods, the discrete element method can retain the discrete nature of rubble-pile structures and can be used to analyze both static and dynamic processes. Some basic problems and potential research interests related to the application of discrete element method on rubble-pile asteroids are suggested.


Funded by

国家自然科学基金(11572166)


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  • Figure 1

    (Color online) Absolute magnitude H vs. orbital semi-major axis a of 523584 numbered asteroids.

  • Figure 2

    (Color online) Spin period vs. diameter of 16075 asteroids whose lightcurve quality is not less than 2.

  • Table 1   Completed or on-going asteroid missions

    €€€任务名称

    €€机构

    €€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€任务描述

    €€€Galileo

    NASA

    1991年近距飞越S型主带小行星951 Gaspra, 1993年近距飞越S型主带小行星243 Ida, 并发现Ida的卫星Dactyl[3]

    €€€NEAR-Shoemaker

    NASA

    1997年近距飞越Cb型主带小行星253 Mathilde, 1998年近距飞越S型近地小行星433 Eros, 2000年与Eros交会进入环绕小行星轨道并于2001年着陆于Eros[4]

    €€€Deep Space 1

    NASA

    1999年近距飞越Q型近地小行星9969 Braille, 2001年近距飞越彗星19P/Borrelly[5,6]

    €€€Cassini

    NASA

    2000年近距飞越S型主带小行星2685 Masursky[7]

    €€€Stardust

    NASA

    2002年近距飞越S型主带小行星5535 Annefrank, 2004年近距飞越彗星81P/Wild 并采集了Wild彗发中的尘埃颗粒(样品舱于2006年返回再入地球大气层), 2011年近距飞越彗星9P/Tempel (观测到了NASA于2005年Deep Impact任务撞击该彗星后的地貌)[8,9]

    €€€Hayabusa

    JAXA

    2005年交会并着陆于S型近地小行星25143 Itokawa, 采集了Itokawa表面细微颗粒(样品舱于2010年返回再入地球大气层)[10]

    €€New Horizons

    NASA

    2006年近距飞越S型主带小行星132524 APL, 2015年近距飞越柯伊伯带矮行星134340 Pluto, 计划2019年近距飞越柯伊伯带天体2014 MU69[11]

    €€€Rosetta

    ESA

    2008年近距飞越E型主带小行星2867 Teins, 2010年近距飞越M型主带小行星21 Lutetia, 2014年与彗星67P/Churyumov-Gerasimenko交会进入环绕彗星轨道并释放着陆器Philae[12]

    €€Dawn

    NASA

    2011年与V型主带小行星4 Vesta交会进入环绕小行星轨道, 2012年离开Vesta, 2015年与C型主带矮行星1 Ceres交会进入环绕矮行星轨道[13]

    €€€Chang’E 2

    CNSA

    2012年近距飞越S型近地小行星4179 Toutatis[14]

    €€€Hayabusa 2

    JAXA

    探测器于2014年发射, 2018年与Cg型近地小行星162173 Ryugu交会实施采样任务并释放着陆器MASCOT, 2020年将样品返回地球[15]

    €€€OSIRIS-REx

    NASA

    探测器于2016年发射, 2018年与B型近地小行星101955 Bennu交会, 2020年实施采样任务并于2023年将样品返回地球[16]

    €€€Lucy

    NASA

    计划于2021年发射, 2025年近距飞越C型主带小行星52246 Donaldjohanson, 2027年至2033年近距飞越五颗不同光谱类型的木星特洛伊小行星

    €€€Psyche

    NASA

    计划于2023年发射, 2030年与M型主带小行星16 Psyche交会进入环绕小行星轨道

  • Table 2   Comparison of methods in rubble-pile asteroids study

    研究方法

    典型代表

    经济代价

    时间代价

    适用领域

    理论分析

    流体、固体及运动稳定性理论

    Ν

    Ν

    结构平衡性与稳定性分析

    实验探索

    微重力实验

    中、高

    中、高

    颗粒材料流动与低速碰撞

    高速撞击实验

    固体及颗粒材料的高速碰撞

    数值模拟

    有限元法

    较低

    较低

    结构应力分布和小变形问题

    无网格法

    较低

    结构超高速碰撞和裂纹扩展问题

    离散元法

    较低

    较高

    结构低速碰撞、平衡稳定性分析与应力分布和变形

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