Achondriteissa

Achondriteissa is a hypothetical designation sometimes cited in discussions of achondrite meteorites to describe a proposed informal subgroup. The name combines achondrite with a suffix suggesting a distinct category, but it is not an officially recognized taxon in the standard meteorite nomenclature.

In speculative schemes, Achondriteissa would be defined by igneous-textured, relatively coarse-grained meteorites with minimal or absent chondrules. Mineral assemblages are described as dominated by pyroxene and plagioclase, with possible minor olivine and calcium-rich minerals. Isotope systematics, such as neodymium-hafnium or silicon isotopes, are proposed as diagnostic tools to distinguish Achondriteissa from established achondrite groups like eucrites and diogenites. Proponents emphasize a magmatic history on a differentiated parent body, with textures and chemistry reflecting crystallization processes in a crustal environment.

Status and reception: Achondriteissa is not formally recognized by the Meteoritical Society and has no official entry in the Meteoritical Bulletin. It appears mainly in speculative literature and some research notes rather than in standardized classifications. Consequently, it remains a concept used to discuss potential variation within achondrite meteorites rather than a defined, widely accepted category.

Origin and implications: If a real group corresponding to Achondriteissa were confirmed, it would imply the existence of a differentiated parent body with a distinct crustal evolution different from known achondrite groups. This would contribute to broader questions about planetary differentiation, crust formation, and the diversity of early solar system bodies.

See also: Achondrite, Eucrite, Diogenite, Howardite, Meteorite classification.