This page displays sample cosmic dust models of the "Bird's-Nest" type (Greenberg and Gustafson, 1981; Gustafson et al., 1998). The scale models used in the microwave analogue laboratory consists of millimeter size plastic cylinders and spheres that have refractive indices in the laboratory wavelength range (2.7 to 4 mm) that, when translated to the visual range, correspond to silicates and organics in submicron particles. The aggregates represent ensembles of interstellar grains of the classical size range and differ in size, packing, mantling, and shape of the constituent grains. Note that the scale is different in each photograph. The particle dimensions are indicated in the text.
All elements of the scattering matrix were measured at 85 frequencies at approximately 1000 orientations and at 165 scattering angles. This amounts to ~15 million measurements requiring two months of laboratory time at the rate of 3 measurements per second. The sample data shown is from a 22 frequency subset has been reduced and calibrated to extract the angular distribution of intensity and polarization in two colors, red and blue. The colors correspond to standard astronomical filters. This is the standard data set shown for each model on this web page.
Model of a cosmic dust particle from a primitive body such as a comet,
consisting of 1650 classic size interstellar dust grains. The scale model
consists of 2 mm length cylinders of 1.25 mm diameter and a refractive
index m = 1.74 + i0.005 at the laboratory wavelength range (2.7
to 4 mm). Scaled to the optical wavelength range, this corresponds to 0.2
micron diameter grains in an aggregate that is 10 micron across. Each grain
in the aggregate is made of a material that has optical properties intermediate
between silicates making up the cores and organic refractories in the mantles
according to the classical interstellar grain model. Here, both the core
and the mantle are therefore represented using a single material in the
laboratory, nylon. The grains are aggregated at random such that the ratio
of volume occupied by material to the total volume gives a porosity ~0.3.
This value is approximate since the volume of the aggregate is hard to
define. The model rests on a support used for display purposes only.
Aggregate of 1650 spheres each of diameter 1.58 mm, material: nylon, m=1.74+i0.005,
porosity ~0.45.Translated to visual wavelengths, this aggregate corresponds
to a BN-type aggregate of 825 classical interstellar grains that is approximately
6 micron across. Each interstellar grain of elongation of 2:1 is represented
using a set of two spheres. The spheres were first assembled into sets
of two and randomly distributed to produce the aggregate.
Aggregate of 500 nylon (m=1.74+i0.005) spheres of diameter 1.58
mm. The porosity is near 0.4. This corresponds to an ensemble of 250 interstellar
grains of similar properties as the aggregate above, except for the number
of grains and the aggregate diameter that corresponds to 3 to 4 micron.
Aggregate formed by loosely wound ball of string of diameter 1.25 mm, material:
nylon, m=1.74+i0.005. This model was used to achieve lower packing
and larger dimater aggregate corresponding to 35 to 40 micron across.
Aggregate of 43 constituent particles of spherical shape of diameter 19 mm , material: nylon, m=1.74+i0.005 , porosity 0.2. This corresponds to 3.5 micron diameter grains in a 30 micron diameter aggregate.
Aggregate of 43 constituent particles of spherical shape of diameter 19 mm , material: nylon, m=1.74+i0.005 , porosity 0.55. This corresponds to 3.5 micron diameter grains in a 20 micron diameter aggregate.
Compact aggregate of 3000 prolate nylon cylinders of 2:1 elongation
ratio and 1.25 mm diameter in an absorbing matrix. This corresponds to
a compacted ensemble of interstellar grains where the chemically highly
reactive organic refractory material of the mantles (m=1.7+i0.05)
fused to form a solid grain with silicate inclusions. This is a possible
model for D-type asteroid material.
Aggregate of 88 irregular but rounded constituent particles of diameter from 3 to 8 mm, made of a pastic compound representing organic refractory material, m=1.7+i0.2. This model was made to simulate aerosols in the atmosphere of Titan.
