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金星水星异常自转的自然形成机制

更新时间 2009-9-12 23:02:02 点击数:

金星水星异常自转的自然形成机制
A Natural Formation Mechanism of the Abnormal Rotation of Venus and Mercury
【中文摘要】 金星的缓慢逆向自转在太阳系行星中是非常独特的。太阳系大多数行星都是快速正向自转,典型的自转周期只有约1天或不到1天,黄赤交角也比较小;而金星的自转周期却长达243天,并且是逆向自转,即自转方向与行星公转方向相反。自从人类发现金星的这一自转特性以来,这一特殊现象的形成原因便成为太阳系演化中的一个重要研究课题。金星目前的自转状态是生来就有的还是后天演变来的,是什么机制使其演变的,这是至今仍然在研究的问题。一般认为,金星原来具有典型的快速正转的状态,在后来的演化过程中,由于潮汐作用或行星内部流体核与幔间的摩擦作用,使得自转逐渐发生变化;也有研究认为可能是早期受到大星子的偶然碰撞所致。各种观点都能说明一些问题,但是都需要各种不同的初始状态,自然形成的概率不大。偶然事件如果真发生过,能说明金星的逆转,但也不能同时解释水星的缓慢转动。本文探讨了金星异常自转形成的一种可能机制,行星际物质的作用。在太阳系各大行星共同形成说的基础上,本文从太阳引力场中行星际物质径向分布的不均匀性假设出发,推导并计算了行星际物质对类地行星自转的影响。我们的研究显示,金星在演化过程中与周围星子和其他行星际物质非对称碰撞可以获得反向角动量,使得金星由典型自转演化到目前状态。用同一理论模型也能解释水星的缓慢自转。全文内容共分为四章。第一章综述,首先介绍了本课题研究需要的基础知识——太阳系大行星的概况和当前太阳系行星形成的基本理论,同时在介绍了人类对水星和金星自转的研究历史和现状的基础上,简介了本课题研究的目的和意义。第二章详细阐述了本课题的第一个研究模型和结果。该模型是在行星共同形成学说的基础上,探讨了行星形成后,径向不均匀分布的行星际物质对金星和水星的自转产生一种可能影响。在粗略的假定行星际物质不随时间变化的情况下,讨论了金星和水星在公转过程中由于行星际物质的作用而损失的角动量,得到金星和水星的自转分别经历50亿年和20亿年,就可能由通常的自转变为目前的异常自转状态。第三章阐述了本课题采用的第二个研究模型,即改进的模型。该模型不仅考虑了实际问题中行星际物质随时间的变化,还同时探讨了行星在公转和自转过程中受行星际物质作用而损失的角动量。研究对象不仅限于金星和水星,还涉及到所有的类地行星。结果更加有说服力的证明,在45亿年之前,所有的类地行星自转都可处在典型的快速正向自转状态,自转变化最大的是金星和水星,在大约35亿年前金星和水星的自转就可能稳定到目前状态。最后一章对本文的工作进行了总结,同时指出了该工作中存在的不足之处和需要进一步改进的问题

【英文摘要】 The slow and retrograde rotation state of Venus is very peculiar among the planets in the solar system. Most planets have fast and direct rotation with a small obliquity, typical rotation period is about or even less than one day; but the rotation period of Venus is 243 days and its rotation is retrograde, that is to say Venus, direction of spin and revolution is opposite. Since the unique rotation state of Venus was discovered, the formation mechanism of the character has been an important researchful question in the evolution of the solar system.It is still a research problem now that the present rotation state is originated with the formation of Venus or evolved from direct to retrograde rotation afer its formation, and what mechanism has made the evolution. It is generally believed that Venus originated with the typical fast and direct rotation. But in the late evolution process, as a result of atmospheric tides and core-mantle friction inside the planet, the rotation is changed gradually. While some others considered that the change of Venus’rotation perhaps due to the early giant planetesimal’s collisions. All these view can explain some questions, but exist some difficulties, the probability would not be very large. At the same time, if occasional emergency really occured, even it can explain the retrograde rotation of Venus, can’t explain the slow rotation of Mercury.In this letter we discuss another possible mechanism that may lead to the abnormal rotation of Venus, the effect of interplanetary matter. On the base of the corporate formation hypothesis of the planets,we calculate the effect on the terrestrial planets spin from the action of interplanetary matter which is asymmetrically distributed in the radial direction. Our results show during the evolution process Venus could have gain reverse angular momentum from the asymmetric collisions with planetesimals and other interstellar matter around, then its rotation evolved to the present state from the typical state.Using the same model we also can explain the slow rotation of Mercury. This paper consists of four chapters.In Chapter 1, we introduced the general situation of the planets in the solar system, showed three formation hypothesis of the solar system and introduced the history and the present study situation of Venus, and the significance and purpose of our study.In Chapter 2, we expatiated our first model and result. On the basis of the corporate formation hypothesis, we discussed a possibility that the effect of asymmetric interplanetary matter changed the rotation of Venus and Mercury since they formed completely. We assumed the density of interplanetary matter were fixed. Our result showed under the assumed conditions, the current rotation of Venus and Mercury could be achieved in 5 billion years and 2 billion years respectively.In Chapter 3, we introduced our ameliorated model. we improved the influence on terrestrial planets spin, including the loss of the angular momentum due to revolution and spin, and the density of interplanetary matter changed versus time. Our results showed all the terrestrial planets were in the typical fast prograde rotation state before 4.5 billion years, and the rotation states of Venus and Mercury remained steady before about 3.5 billion years.In Chapter 4, we made a conclusion about our work, pointed out the simplicities and problems to be modified in our future work.

【中文关键词】 金星; 水星; 角动量; 自转周期; 行星际物质
【英文关键词】 Venus; Mercury; angular momentum; spin period; interplanetary matter
毕业论文目录】
中文摘要 6-8
英文摘要 8-9
第一章 综述 10-22
    1.1 太阳系大行星的基本概况 10-13
    1.2 太阳系行星的形成机制 13-16
        1.2.1 行星形成的灾变说 13-14
        1.2.2 行星形成的俘获说 14-15
        1.2.3 太阳系共同形成学说 15
        1.2.4 各种学说评价及比较 15-16
    1.3 金星水星自转的研究历史和现状 16-20
        1.3.1 潮汐和核幔摩擦说 17-18
        1.3.2 大星子碰撞说 18
        1.3.3 共振说 18-19
        1.3.4 Correia Alexandre 的数值模拟研究 19
        1.3.5 问题 19-20
    1.4 本文研究的目的和意义 20-22
第二章 行星际物质对金星水星自转影响初探 22-30
    2.1 理论依据和模型 22-27
        2.1.1 介质密度分布的确定 22-25
        2.1.2 计算模型 25-27
    2.2 计算结果 27-29
        2.2.1 金星的计算和结果 27-28
        2.2.2 水星的计算结果 28-29
    2.3 本章结果讨论 29-30
第三章 行星际物质对自转影响的改进探究 30-39
    3.1 理论依据和计算模型 30-34
        3.1.1 行星公转获得的角动量 31-32
        3.1.2 行星自转获得的角动量 32-33
        3.1.3 行星际物质影响行星自转的总效果 33-34
    3.2 计算结果及分析 34-39
        3.2.1 行星自转角速度变化的比较 34
        3.2.2 金星自转的变化 34-37
        3.2.3 水星自转的变化 37
        3.2.4 火星可能的原始自转状态 37-38
        3.2.5 小结 38-39
第四章 总结与讨论 39-42
    4.1 结论 39
    4.2 问题讨论 39-42
参考文献 42-50
攻读硕士学位期间发表的论文 50-51
致谢 51

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