Physics and chemistry of icy particles in the universe:: answers from microgravity

During the last century, the presence of icy particles throughout the universe has been confirmed by numerous ground and space based observations. Ultrathin icy layers are known to cover dust particles within the cold regions of the interstellar medium, and drive a rich chemistry in energetic star-forming regions. The polar caps of terrestrial planets, as well as most of the outer-solar-system satellites, are covered with an icy surface. Smaller solar system bodies, such as comets and Kuiper Belt Objects (KBOs), contain a significant fraction of icy materials. Icy particles are also present in planetary atmospheres and play an important role in determining the climate and the environmental conditions on our host planet, Earth. Water ice seems universal in space and is by far the most abundant condensed-phase species in our universe. Many research groups have focused their efforts on understanding the physical and chemical nature of water ice. However, open questions remain as to whether ices produced in Earth's laboratories are indeed good analogs for ices observed in space environments. Although temperature and pressure conditions can be very well controlled in the laboratory, it is very difficult to Simulate the time-scales and gravity conditions of space environments. The bulk structure of ice, and the catalytic properties of the surface, could be rather different when formed in zero gravity in space. The author list comprises the members of the ESA Topical Team: Physico-chemistry of ices in space. In this paper we present recent results including ground-based experiments on ice and dust, models as well as related space experiments performed under microgravity conditions. We also investigate the possibilities of designing a new infrastructure, and/or making improvements to the existing hardware in order to study ices on the International Space Station (ISS). The type of multidisciplinary facility that we describe will support research in crystal growth of ices and other solid refractory materials, aerosol microphysics, light scattering properties of solid particles, the physics of icy particle aggregates, and radiation processing of molecular ices. Studying ices in microgravity conditions will provide us with fundamental data on the nature of extraterrestrial ices and allow us to enhance our knowledge on the physical and chemical processes prevailing in different space environments. (C) 2003 Elsevier Science Ltd. All rights reserved.