Much of a planet's composition could be determined right at the onset of
formation. Laboratory experiments can constrain these early steps. This
includes static tensile strength measurements or collisions carried out under
Earth's gravity and on various microgravity platforms. Among the variety of
extrasolar planets which eventually form are (Exo)-Mercury, terrestrial planets
with high density. If they form in inner protoplanetary disks, high temperature
experiments are mandatory but they are still rare. Beyond the initial process
of hit-and-stick collisions, some additional selective processing might be
needed to explain Mercury. In analogy to icy worlds, such planets might, e.g.,
form in environments which are enriched in iron. This requires methods to
separate iron and silicate at early stages. Photophoresis might be one viable
way. Mercury and Mercury-like planets might also form due to the ferromagnetic
properties of iron and mechanisms like magnetic aggregation in disk magnetic
fields might become important. This review highlights some of the mechanisms
with the potential to trigger Mercury formation.Comment: This article belongs to the Special Issue of Geosciences: Detection
and Characterization of Extrasolar Planet
