Micrometeorites (MMs) are small extraterrestrial particles, with sizes ranging typically from about 50 µm to 1 mm, collected on the Earth's surface (Maurette, 2006). They are collected with different techniques and in different parts of the world, such as the recovery of cosmic spherules from deep-sea sediments, the melting of ice in the Greenland and Antarctica, and collection in Antarctic high-altitude sediment deposits. Micrometeorites are generally classified by the degree of heating they experienced during Earthâs atmosphere entrance, which depends on their initial speed and angle of entry (Genge et al., 2008):
Micrometeorites are of particular interest, as previous studies suggested that they might have contributed a significant amount of water and organics to the early Earth (Maurette, 2006). However the origin(s) of MMs and their possible relationships to other extraterrestrial materials (primitive meteorites and IDPs) are still debated, and both asteroidal (related to carbonaceous chondrites) and cometary origins have been proposed. Chemical and mineralogical studies have suggested a connection between MMs and carbonaceous chondrites (Kurat et al., 1994), and fragments or relics of chondritic components, such as chondrules, calcium-aluminum-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), have also been reported in MMs (Genge et al., 2008; Yada et al., 2005). Oxygen isotopic analyses of bulk MMs and individual minerals in MMs are also consistent with a connection to carbonaceous chondrites (Matrajt et al., 2006; Suavet et al., 2010). However, other studies have proposed that at least a small portion of the micrometeorite collection might constitute a separate population of Solar System material originating from the outer Solar System and delivered to the inner Solar System by comets (Engrand and Maurette, 1998). In particular, ultracarbonaceous MMs (consisting of up to 90% of carbonaceous matter) have been shown to exhibit large deuterium excesses, consistent with a possible cometary origin (Duprat et al., 2010).