The role of laboratory experiments in the
characterisation of silicon-based cosmic material
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Abstract
Silicate grains in space have attracted
recently a wide interest of astrophysicists due
to the increasing amount and quality of
observational data, especially thanks to the
results obtained by the Infrared Space
Observatory. The observations have shown that the
presence of silicates is ubiquitous in space and
that their properties vary with environmental
characteristics. Silicates, together with carbon,
are the principal components of solid matter in
space. Since their formation, silicate grains
cross many environments characterised by
different physical and chemical conditions which
can induce changes to their nature. Moreover, the
transformations experienced in the interplay of
silicate grains and the medium where they are
dipped, are part of a series of processes which
are the subject of possible changes in the nature
of the space environment itself. Then, chemical
and physical changes of silicate grains during
their life play a key role in the chemical
evolution of the entire Galaxy. The knowledge of
silicate properties related to the conditions
where they are found in space is strictly related
to the study in the laboratory of the possible
formation and transformation mechanisms they
experience. The application of production and
processing methods, capable to reproduce actual
space conditions, together with the use of
analytical techniques to investigate the nature
of the material samples, form a subject of a
complex laboratory experimental approach directed
to the understanding of cosmic matter. The goal
of the present paper is to review the
experimental methods applied in various
laboratories to the simulation and
characterisation of cosmic silicate analogues.
The paper describes also laboratory studies of
the chemical reactions undergone and induced by
silicate grains. The comparison of available
laboratory results with observational data shows
the essential constraints imposed by astronomical
observations and, at the same time, indicates the
most puzzling problems that deserve particular
attention for the future. The outstanding open
problems are reported and discussed. The final
purpose of this paper is to provide an overview
of the present stage of knowledge about silicates
in space and to provide to the reader some
indication of the future developments in the
field