Can Composite Fluffy Dust Particles Solve the Interstellar Carbon Crisis?

Recent observations suggest that the abundance of carbon in the interstellar medium is only D60% of its solar value, and that other heavy elements may be depleted by a similar amount. Furthermore, more than half of the interstellar carbon is observed to be in the gas in the form of C`, leaving less than D40% of the solar carbon abundance available for the dust phase. These observations have created the so-called interstellar carbon crisis, since traditional interstellar dust models require about twice that value to be tied up in graphite grains in order to explain the interstellar extinction curve.