A Research Programme on the Dynamics of Discs and Planets

1995年，一组瑞士天文学家发现了太阳系外第一颗围绕类太阳恒星运行的真正行星。自那时以来，国际科学家团队总共发现了350多颗太阳系外行星。这些行星系统中的大多数具有与太阳系非常不同的结构，这引发了许多关于这些行星是如何形成和演化的问题。据信，行星是在年轻恒星周围观察到的气体和尘埃盘--所谓的原恒星盘--中形成的。尽管存在很大的不确定性，但行星形成的基本图景已经出现。第一个阶段涉及盘内微小尘埃颗粒的凝聚，当它们碰撞形成更大的鹅卵石时，它们会粘在一起。这一过程一直持续到形成更大的天体，大小约为10公里。这些天体被称为行星体，其中一些能够通过与其他行星体的碰撞而快速增长，形成行星。在距离中央恒星很远的地方，原行星盘中的温度降至较低的值，水和其他挥发性化合物从气体中凝结出来形成冰粒。这具有显著增加固体物质数量的效果，并允许形成非常大的固体行星物体，这些物体可以从圆盘中吸引大量气体成为气态巨行星，类似于木星和土星。在圆盘较温暖的内部区域，冰粒不能形成，因此预计会形成较小的岩石行星，如地球和金星。上述行星形成过程的每个阶段都有许多理论上的不确定性，剑桥的艾萨克·牛顿研究所正在主持一个为期四个月的研究方案，旨在解决一些这些悬而未决的理论问题。这方面的大多数领先的国际研究人员都将参加该计划，这将为在理解行星系统如何形成和演化方面取得重大进展提供一个非常令人兴奋的机会。

The first bona fide planet orbiting a sun-like star outside of the solar system was discovered by a team of Swiss astronomers in 1995. Since this time, teams of international scientists have collectively discovered in excess of 350 extrasolar planets. Most of these planetary systems have very different architectures to the Solar System, raising many questions about how these planets formed and evolved. It is believed that planets form in the discs of gas and dust that are observed around young stars - so-called protostellar discs. Although there are significant uncertainties, a basic picture of planet formation has emerged. The first stage involves coagulation of small dust particles within the disc, which stick together when they collide to form larger pebbles. This process continues until larger bodies, with sizes approximately 10km, are formed. These bodies are called planetesimals, some of which are able to grow at a rapid rate through collisions with other planetesimals to form planets. At large distances from the central star, where the temperature in the protoplanetary disc falls to low values, water and other volatile compounds condense out of the gas to form ice grains. This has the effect of substantially increasing the amount of solid material, and allows very big solid planetary objects to form which can attract a large amount of gas from the disc to become gas giant planets, similar to Jupiter and Saturn. In the warmer inner regions of the disc, ice grains cannot form and so smaller rocky planets such as the Earth and Venus are expected to form. There are many theoretical uncertainties associated with each stage of the planet formation process described above, and the Isaac Newton Institute in Cambridge is hosting a four-month research programme aimed at solving some these outstanding theoretical problems. Most of the leading international researchers in this are will be attending the programme, providing a very exciting opportunity for making significant progress in understanding how planetary systems form and evolve.