Density of Ices of Astrophysical Interest

Abstract

Density plays an important role in the understanding of chemical and physical evolution of ices in space. It is related with abundances, energetic processing, porosity, buoyancy, etc.

The experimental values available are scarce and, often, corresponding to ices without pores (bulk density) despite many experiments devoted to astrophysics form porous ices. Additionally, ice density frequently depends on the formation temperature, and these studies are even scarcer.

In this chapter, bulk and average density are defined, and experimental methods to determine both densities are reviewed. Ice density values are presented covering from the lighter to the denser ones. The relationship between density and ice structure is exemplified. The examples cover temperature phase transitions, amorphous and crystalline structures. The possibility to detect metastable crystalline structures is also proposed. The case of ice mixtures is presented to warning about the impossibility to obtain density values from those of the pure constituents. Finally, ice porosity experimentally obtained is tabulated to reveal that high density ices (>1 g cm⁻³) can be as porous as low density ices (<0.5 g cm⁻³).