In the 1970s, an apparatus for synthesizing an analogue of interstellar organic dust was developed by Dr. Akira Sakata and collaborators at the University of Electro-Communications. The apparatus employs a 2.45 GHz microwave source to generate plasma from methane gas, which is subsequently quenched and condensed to produce Quenched Carbonaceous Composite (QCC; Sakata et al. 1983, 1984). This synthesis method qualitatively simulates the condensation of organic dust around red giant stars, and QCC has since been widely used as a carbonaceous analogue of interstellar dust.

Since 2007, the apparatus has been transferred to the University of Tokyo, where experimental studies have continued. Later, we have successfully synthesized Quenched Nitrogen-included Carbonaceous Composite (QNCC; Endo et al. 2021) by quenching and condensing plasma generated from nitrogen gas and hydrocarbon dust. QNCC remarkably well reproduces the infrared spectral characteristics of unidentified infrared (UIR) band observed in classical novae. Furthermore, it exhibits infrared spectroscopic characteristics similar to those of the insoluble organic matter (IOM) found in carbonaceous meteorites. Detailed analyses have shown that QNCC (1) is a composite carbonaceous material containing both aliphatic and aromatic components, dominated by amorphous sp³-bonded carbon similar to diamond-like carbon (DLC); (2) consists primarily of hydrogen-terminated sp³ carbon structures with smaller contributions from alkyl functional groups; and (3) contains nitrogen in the form of pyridinic and pyrrolic species, as well as amine structures bonded to sp³ carbon (Senoo et al. 2026, Geochemical Journal, in press).

The origin of complex organic matter in the Universe has traditionally been discussed within the framework of bottom-up chemical evolution, in which all carbon is initially assumed to exist as ionized carbon atoms and progressively forms increasingly complex molecules through gas-phase and grain-surface reactions during star formation. However, recent observations of nearby molecular clouds have revealed abundances of large organic molecules that are difficult to reconcile with conventional bottom-up chemical network models alone. We therefore propose that an additional top-down evolutionary pathway should be considered, in which organic dust grains ejected by evolved stars survive their journey through the interstellar medium, are incorporated into primordial molecular clouds, and subsequently fragment to supply complex organic molecules. To investigate whether this top-down mechanism can serve as an efficient source of complex organic matter in star- and planet-forming environments, we continue experimental studies of QNCC and its physical and chemical properties.

More than fifty years have passed since the original synthesis apparatus was constructed. To further advance experimental studies of interstellar organic dust and expand their application to astrobiology, the development of a new synthesis system became essential. We have therefore designed and constructed a new apparatus that preserves the original principle of synthesizing laboratory dust by quenching plasma generated with a 2.45 GHz microwave source while incorporating significantly improved instrumentation to ensure higher reproducibility of experimental conditions and enhanced analytical capability for determining the elemental composition of the plasma. In this presentation, we will introduce the design concept and key features of the new QCC/QNCC synthesis apparatus and present preliminary results of plasma compositional analyses obtained using a plasma process monitor.