Thermo-chemical evolution of ice-silicate bodies: Application to Ceres

谷神星是小行星带中最大的天体，半径约470公里。谷神星与帕拉斯和灶神星一起被认为是一颗原行星，可以被视为行星吸积中间阶段的剩余例子之一，这与大多数小行星还有很大的不同。其约2077公斤/立方米的低密度表明，如果平均孔隙度可以忽略不计，全球冰的质量分数为17-27%。此外，由于26Al等短寿命放射性元素的加热，CERES在演化早期分化，并由硅酸盐-铁核和上层冰层组成。在本项目中，我们打算用新的数值模型来研究CERES的热化学演化。谷神星是黎明号航天器的第二个目标，它将于2015年春季进入轨道。曙光肯定会提供谷神星的形状、密度、结构、表面和组成的数据；因此，在到达目标之前和之后的数值模拟将使之能够跟上观测的步伐，并有助于建立最可能的演化情景。为了研究CERES的热化学演化，我们将考虑与冰体相关的各种过程，如无定形到结晶冰的转变，冰的融化和热液对流，硅酸盐的水化和脱水反应，冰和硅酸盐的分异，硅酸盐和可能的铁熔化。其目的是根据其组成、相对于富钙铝包裹体的形成时间(CAI)和沉积持续时间，找到该岩体可能的演化情景和内部结构。我们将进一步提供对其他结冰天体的更好了解，如结冰的小行星和卫星。

Ceres is the largest body in the asteroid belt having the radius of ~470 km. Considered as a protoplanet along with Pallas and Vesta, Ceres can be seen as one of the remaining examples of the intermediate stages of planetary accretion, which additionally is considerably different from most asteroids. Its low bulk density of about 2077 kg/m3 suggests a global ice mass fraction of 17 - 27 % if the average porosity is negligible. Furthermore, it is suggested that Ceres differentiated early in its evolution due to heating of short-lived radioactive elements such as 26Al and consists of a silicate-iron core and an upper ice layer.In this project, we intend to study the thermo-chemical evolution of Ceres with a new numerical model. Ceres is the second target of the Dawn spacecraft, which will enter its orbit in spring 2015. Dawn will most certainly provide data of the shape, density, structure, surface and composition of Ceres; thus, numerical modelling prior to and after the arrival at the target will allow to keep pace with the observation and help to establish the most likely evolution scenario. To study the thermo-chemical evolution of Ceres we will consider the various processes relevant for icy bodies like amorphous to crystalline ice transition, melting of ice and hydrothermal convection, hydration and dehydration reactions of the silicate, differentiation of ice and silicates, silicate and possible iron melting. The aim is to find likely evolution scenarios and interior structures of this body depending on its composition, formation time relative to the calcium-aluminium-rich inclusions (CAIs) and accretion duration. We will further provide a better understanding of other icy bodies like icy asteroids and satellites.