Environmental Engineering Reference
In-Depth Information
Fig. 2.3 Sources of cosmic
dust on Earth [
38
]
Interplanetary dust composition and size were measured based on IR detection,
during space missions like Pioneer 10 and 11, Giotto and Galileo. Similar mea-
surements were taken under the EURECA programme, with satellites in circumter-
restrial orbits situated at different distances. The studies conducted in the field were
completed with data collected in the exosphere, at an altitude of 20-25 km.
This older or more recent research work reveals that cosmic dust consists of
microparticles, nanoparticles and their aggregates. These are irregular-shaped and
their porosity varies from spongy to compact. Their composition, size and physico-
chemical properties are origin-dependent. For instance, the grains in dense matter
interstellar clouds are covered in ice; consequently, they are much larger than dust
particles in diffuse interstellar medium. Interplanetary dust particles (IDP) are
usually the largest.
The largest fraction of the extra-terrestrial dust influx falling on Earth comes
from meteorites in the 50-500
m size range, 2.0 g/cm
3
average density and 40 %
porosity. The density of most IDP captured in the atmosphere ranges between 1 and
3 g/cm
3
, with an average of 2.0 g/cm
3
[
38
].
Interstellar dust clouds contain carbon monoxide, silicon carbide, amorphous
calcium silicate, water ice and polynuclear aromatic hydrocarbons (PAH) or other
simpler organic structures, while in diffuse interstellar medium carbon and silicon
particles have been identified.
Comet dust differs in composition from dust resulted from asteroid disintegra-
tion. The former is closer to interstellar clouds, while the latter contain large
amounts of silicon and iron [
39
-
41
].
A recent study [
42
] has identified the proportions of different element forms—
hydrogen, oxygen, carbon, nitrogen—in comet dust samples collected during space
missions. The relations between these elements provide information about the
distance between the Sun and the place where comets were formed and what type
of existence comets had (a high temperature is an indication that they passed close
to the Sun).
μ
