The entry of small celestial bodies such as cometary nuclei, asteroids and their large fragments, into a planetary atmosphere is accompanied by an “explosion”, i.e., sudden rise in brightness and the generation of a “blast” shock wave, like the 2013 Chelyabinsk event. Fully analytic approach to the phenomenon is developed taking into account aerodynamic crushing of the body and transversal expansion of the crushed mass, that leads to impulse generation of hot plasma and a “blast” shock wave in the thin “exploding” layer.

Cloud formation modelling has entered astrophysics as a new field of research for planetary and brown dwarf atmospheres. Clouds are a chemically and physically very active component of an atmosphere since they determine the remaining gas phase and change the object's albedo depending on their material composition. The grains can also provide a surface where the molecular constituents for life can be physisorbed for possible pre-biotic evolution. This paper summarizes our model for the kinetic formation of dirty dust grains which make up the atmospheric clouds of extraterrestrial giant gas planets. We include seed formation, surface growth and evaporation, the gravitational settling that influences the dust formation, element depletion that determines the remaining gas phase abundances, and convective overshooting that is needed for a dust model to be applicable to hydrostatic atmosphere simulations. We demonstrate the evolution of the material composition of the cloud itself and the distribution of the grain sizes in the cloud layer, exemplary for a giant gas planet parameter combinations (Teff, log g). In general, substellar clouds are composed of small, dirty grains with a high silicate content at the cloud deck. They grow in size and gradually purify to iron/corundum grains when they move into denser and hotter atmospheric regions. Comparing these results with experimental data from condensation experiments leads to the conclusion that cloud grains that gravitationally settle in the atmosphere of a giant planet can easily change their lattice structure from the disordered amorphous state they are forming in, into the ordered lattice of a crystal.

Giant gas-planets - and brown dwarfs - form dust clouds in their atmospheres which are made of a variety of gemstone-like and possible liquid materials. Our theoretical approach, where we calculate homogeneous nucleation, heterogeneous growth/evaporation, gravitational settling, and element consumption for composite dust grains, allows to access the evolution of the dust complex in the cloud, and hence also the elements remaining in the gas phase. The cloud formation process is imprinted into these remaining elements. Following a (T, p) trajectory into the atmosphere we observe that 1. metals disappear, 2. dust forms, 3. metals re-appear, 4. dust disappears. For the first time, our kinetic cloud formation approach is coupled with an 1D atmosphere simulation and, hence, synthetic spectra can be produced based on detailed cloud micro-physics. Results are demonstrated for metal-poor gas giants and the strong influence of the dust modelling on alkali-line profile is shown.