Dusty plasmas are widely observed in many astrophysical objects such as molecular clouds , protoplanetary disks, and our solar system. Dust grains are made of silicates, metals, and organic materials but we are particularly interested in ice dust grains.  The composition and abundance of ice dust grains vary among the objects but the major component is water ice. In addition to water ice, ice grains made of ammonia, carbon monoxide, carbon dioxide, methane, methanol, ethane, and ethanol have been observed, although the mass fractions of these ices are small compared to that of water ices. The ice grains are typically formed by condensation of gas-phase elements on cold dust grains composed of refractory materials such as silicate.

Ice dust grains made of water and other materials including alcohols play a critical role in astrophysical objects. They stick dust grains together like glue and help to form planetesimals. Ice grains are also involved in the synthesis of complex organic molecules. The surface of ice grains is the place where important astronomical molecules such as alcohols and sugars are synthesized from simple molecules. Moreover, ice grains control the thermal properties of the astrophysical objects by absorbing and re-emitting the starlight.

The growth and morphology of ice grains in these objects have attracted recent attention. For instance, the growth mechanism of dust grains including ice grains in protoplanetary disks is not completely understood. Infrared spectroscopy and dust growth simulations have revealed that dust grains grow relatively fast until the dust grains become micrometer-sized. However, there is no consensus on how small dust grains of a few micrometers overcome growth barriers such as bouncing barriers and radial-drift barriers and form kilometer-sized planetesimals. The morphology of ice grains is also critical because the surface of ice grains is where chemical reactions occur. Thus, the abundance of compound molecules strongly depends on the surface area and features of the ice dust grains.

In many astrophysical objects, dust grains including ice grains are formed in a plasma environment where electrons and ions exist. If there is a sufficient number of charged particles near the dust grains, they are electrically charged by collisions with electrons and ions. Typically, dust grains are charged with the same polarity so a repulsive force is exerted between dust grains. This could hinder the agglomeration of the dust grains.

Dust growth and shape formed in actual astrophysical objects is not directly observable. Thus, laboratory experiment is necessary to understand what is happening to cosmic dusts. To do so, we built tabletop apparatus at Caltech and KAERI (see figure a) and study astrophysically relevant ice dusts using the apparatus. Our previous studies showed that elongated and fractal-like water-ice grains form in a plasma environment as seen in figure b.