考虑准束缚态过程的彗星尘埃动力学演化及冰含量分析

Comets are the building blocks of the solar system planets, and the fundamental subjects towards understanding the origin and formation of the solar system. Observations and theoretical studies of cometary dust demonstrated that the large-scale spatial distribution and temporal evolution of cometary comae and tails are determined by the dynamical processes of cometary dust. However, the current models do not take into account the existence of quasi-bound dust grains, which were first discovered around the nucleus of 103P/Hartley 2 and then observed again around the nucleus of 67P/Churyumov-Gerasimenko recently, suggesting that quasi-bound dust is a general phenomenon in comets. In this project, we plan to use ground-based and spacecraft images of those two comets to build a high-precision dynamical model of cometary dust, emphasizing quasi-bound grains. We will include gas drag, recoil forces from ice sublimation, the gravitational forces of the Sun and the comet, solar radiation pressure and Poynting-Robertson effect, etc. in our studies. We plan to use Encke method to solve the dynamical processes. The model will be compared to observational data to determine the fundamental properties of the dust of 103P and 67P, such as their ice content and the sublimation process. The proposed study helps us to distinguish the coma source of water vapor from the nucleus source, and is expected to have a broad impact on the observations and studies of the properties of comets and their evolution in general, as well as providing the basis for future cometary exploration missions.

彗星是形成外太阳系行星的基本材料，是研究太阳系起源和演化的重要手段和途径。对彗星尘埃的观测数据和数值模拟表明尘埃动力学过程决定了彗发彗尾的尘埃分布和演化，但以往的研究没有考虑准束缚态尘埃动力学过程对于大尺度尘埃分布演化的影响及其与尘埃冰含量、气体挥发率等基本物理性质的依赖关系。本项目拟使用地面和探测器观测的图像数据，综合考虑多种力场和效应，对已被证实存在准束缚态尘埃的彗星103P和67P建立高精度彗星尘埃多体动力学模型并利用Encke法进行求解，研究彗星尘埃的时空分布规律。通过上述动力学过程研究和对彗发彗尾形状的模拟拟合，推测尘埃冰含量及冰的挥发过程特性等基本物理性质。本研究用动力学手段及地面观测的大尺度彗发彗尾形态推测尘埃冰含量，解决了地面观测无法区分水汽是源于彗核挥发还是尘埃挥发的问题，对研究彗核本身的基本性质和演化过程有重要意义，为我国即将要开展的彗星探测项目提供理论依据和技术支持。

彗星是由形成外太阳系行星的基本材料构成的，是研究太阳系起源和演化的重要手段和途径。对彗星尘埃的观测数据和数值模拟表明尘埃动力学过程决定了彗发彗尾的尘埃分布和演化，但以往的研究没有考虑准束缚态尘埃动力学过程对于大尺度尘埃分布演化的影响及其与尘埃冰含量、气体挥发率等基本物理性质的依赖关系。本项目使用地面和探测器观测的图像数据，综合考虑多种力场和效应，对推测存在准束缚态尘埃的彗星103P建立了高精度彗星尘埃多体动力学模型并利用数值方法进行求解，研究彗星尘埃的时空分布规律。本研究利用机器学习方法，通过训练仿真图像形成了参数-图像训练模型，并利用观测数据对4个关键动力学参数了进行拟合。结果表明，103P彗星尘埃尺寸服从下限约为2微米、系数约为-4.3的幂律分布，尘埃平均逃逸速度约为90m/s，速度方向集中度参数约为0.64。此外，对含冰尘埃进行的动力学仿真表明，尘埃环绕对尘埃自身冰含量不敏感。尺寸小于1m的尘埃最大环绕角度仅为90°，而可完成准束缚环绕的尘埃半径下限高达10米，该结论表明准束缚态尘埃无法稳定存在。进一步的彗核表面热力学研究表明，彗星水冰挥发可能仍然主要是由彗核产生的。