Comets as laboratories: observing and modelling cometary spectra

彗星本身就是重要的太阳系天体，几代天文学家对它们的研究帮助我们了解了它们的性质和行为。它们是巨大的水和其他冰块的水库--肮脏的雪球。但它们也很重要，因为它们保存了早期太阳星云的条件--特别是化学成分--的记录，太阳和行星就是从星云中形成的。它们可能是产生生物前分子的来源之一，生物前分子是生命本身进化的基石。多年来，人们一直认为彗星要么起源于埃奇沃斯-柯伊伯带，该带始于距太阳约50个天文距离，并延伸约50个天文单位，要么来自奥尔特云，介于50,000到100,000个天文单位之间。--距离最近的恒星比邻星大约25%的距离。(Nb天文单位，或称天文单位，是指地球到太阳的距离，约为1.5亿公里。)那么，我们如何更好地了解这些迷人的天体呢？一种方法是研究它们发出的光。像太阳系中的许多其他天体一样，彗星本身并不产生可见光。相反，他们吸收太阳光，并将其转化为红外辐射热。对这种辐射至关重要的是，它告诉我们组成彗星的分子--化学成分--它们有多少，甚至它们的温度有多高。这一分子指纹使天文学家能够了解彗星，以及彗星如何在朝向太阳并再次进入太阳系遥远的区域时演化。所以彗星的行为就像巨大的实验室。一些红外线发射是由于彗核被阳光简单地加热而产生的，变暖导致它们释放气体形成彗发，并形成我们在夜空中看到的耀眼的尾巴，当它们接近太阳时。但其他排放是由更复杂的过程造成的。在距离原子核数千公里的彗发中，这种辐射是由所谓的“泵送”产生的，因为阳光使单个分子高度受热，然后放松。目前，我们的彗星模型要么处理靠近核心的区域，要么处理远离核心的区域。但“介于两者之间”又如何呢？这就是我们的项目旨在了解的。电子--高能带电粒子--在彗星气体发出红外辐射的过程中发挥了关键作用吗？还是冰晶受到紫外线辐射的冲击而受热？这就是这个项目要找出的答案。通过这样做，我们将更好地了解彗星是如何演化的，并反过来在决定太阳系作为一个整体如何演化的过程中发挥作用。敬请关注！

Comets are important solar system bodies in their own right, and their study over many generations of astronomers has helped us understand their properties and behaviour. They are vast reservoirs of water and other ices - dirty snowballs. But they are also important since they preserve a record of conditions - particularly the chemical composition - of the early solar nebula, from which the Sun and planets formed. And they may be [one of] the sources that give rise to pre-biotic molecules, the building blocks from which life itself evolved. For many years, it has been understood that comets originate either from the Edgeworth-Kuiper Belt, which commences around 50 astronomical from the Sun, and extends of ~ another 50a.u., or from the Oort Cloud, at between 50,000 and 100,000 a.u. - roughly 25% of the way to the nearest star, Proxima Centauri. (NB an astronomical unit, or a.u., is the distance from the Earth to the Sun, roughly 150 million kilometers.) So how are we to get a better understanding of these fascinating bodies. One way is to study the light that they emit. Like many other bodies in the solar system, comets do not generate their own visible light. Instead they absorbed sunlight and turn that into infrared radiation - heat. And what is critical to this radiation is that it tells about the molecules that make up the comet - the chemical composition - how many of them they are, and even how hot they are. This molecular fingerprint enables astronomers to understand comets, and how the evolve as they make their way towards the Sun and out again into the distant reaches of the Solar System. So comets act like giant laboratories. Some of the infrared emission results from the simple warming of the cometary nucleus by sunlight, warming that causes them to give off gases to form a coma, and to develop the showy tails that we see in the night sky as they approach the Sun. But other emissions are caused by more complicated processes. Way out in the coma, thousands of kilometers from the nucleus, the emission results from what is known as 'pumping' as the sunlight causes individual molecules to be highly energised, and then relax. At present, our models of comets deal either with regions close in to the nucleus or far away from it. But what about the 'in between'? That is what our project aims to understand. Do electrons - energetic electrically charged particles - play a key role in making the cometary gases give off infrared radiation? Or are ice crystals shock heated by ultraviolet radiation? That's what this project aims to find out. And, in so doing, we will better understand how comets evolve and - in turn - play their part in determining how the Solar System as a whole evolves. Stay tuned!