The Many Influences on Comets' Tails

彗星的冰核通常只有几公里宽，携带着关于我们太阳系起源的宝贵信息。此外，当它们被太阳加热时释放气体和尘埃的过程，以及这些物质离开原子核后的行为，告诉我们关于每颗彗星周围环境的许多信息。彗星释放出的尘埃颗粒沿着受太阳辐射影响的太阳轨道运行：撞击这些微小颗粒的光子将它们推向与太阳引力场相反的方向，形成尘埃尾巴。对于非常小的颗粒，这种辐射力可以强大到足以克服重力，并可以将它们吹出太阳系！释放的气体被电离，加入太阳风的流动。这些动态发光的离子尾巴告诉我们彗星活动水平的变化和太阳风本身的变化(例如Ramajooloo&Jones 2022)。我们小组最近的工作也揭示了太阳风对尘埃尾巴的影响(例如Price+2019,2022)：我们发现了大量的尘埃尾巴，通过我们不完全了解的过程，来自太阳的带电物质的快速流动的影响塑造和重新排列。这一博士项目将以这项诱人的工作为基础，通过分析地球上专业和业余天文学家、主要为研究太阳及其附近环境而设计的天基成像仪以及新收集的图像，分析成像数据。除了帮助我们更好地了解阳光和太阳风对彗星尘埃和离子尾巴的预期影响之外，这项研究还将涉及寻找太阳风对尘埃尾巴影响的进一步证据，并通过太阳轨道飞行器上的仪器应用我们对太阳风结构的理解，试图确定特别是负责重新排列尘埃尾巴物质的过程。这项研究的结果预计将有助于欧空局定于2029年发射的彗星拦截任务的准备工作。

Comets' icy nuclei, typically measuring only a few kilometres across, carry invaluable information on the origins of our Solar System. In addition, the processes through which they release gas and dust when heated by the Sun, and the behaviour of that material after it leaves the nucleus, tells us a great deal about the environment surrounding each comet. The dust grains that are released from comets follow orbits around the Sun that are affected by the solar radiation: photons striking these tiny grains push them away in the direction opposite to the pull of the Sun's gravitational field, creating a dust tail. For very small grains, this radiation force can be strong enough to overcome gravity and can blow them out of the solar system! The gases that are released get ionized, and join the flow of the solar wind. These dynamic, glowing ion tails tell us about the changing activity levels of the comet and the variations in the solar wind itself (e.g. Ramajooloo & Jones 2022).Recent work in our group has revealed strong evidence of solar wind effects on dust tails too (e.g. Price+ 2019, 2022): extensive dust tails have been found to be moulded and re-arranged by the effects of the fast flow of charged material from the Sun, through processes that we don't fully understand. This PhD project would build upon this tantalizing work, through the analysis of imaging data obtained by professional and amateur astronomers on Earth, by space-based imagers that are primarily designed to study the Sun and its near-environment, and with newly-gathered images. As well as helping us better understand the expected influence of sunlight and the solar wind on the comets' dust and ion tails, the research would involve searching for further evidence for the solar wind's effects on dust tails, and applying our understanding of structures in the solar wind through instruments such as those on the Solar Orbiter spacecraft, to try to determine the processes responsible for rearranging dust tail material in particular. The outcome of this research is expected to benefit preparations for ESA's Comet Interceptor mission, due for launch in 2029.