  It is difficult to study the interiors of terrestrial planets in the Solar
System and the problem is magnified for distant exoplanets. However, sometimes
nature is helpful. Some planetary bodies are torn to fragments and consumed by
the strong gravity close to the descendants of Sun-like stars, white dwarfs. We
can deduce the general composition of the planet when we observe the
spectroscopic signature of the white dwarf. Most planetary fragments that fall
into white dwarfs appear to be rocky with a variable fraction of associated ice
and carbon. These white dwarf planetary systems provide a unique opportunity to
study the geology of exoplanetary systems.
