Allan Hills A77005 Martian meteorite, Allan Hills, Victoria Land, Eastern Antarctica, Antarcticai

Regional Level Types
Allan Hills A77005 Martian meteorite	Meteorite Fall Location
Allan Hills	Group of Hills
Victoria Land	Region
Eastern Antarctica	Region
Antarctica	Continent

Shergottite, lherzolitic
Find, 1977; 483 g

A small ellipsoidal stone (~9.5x7.5x5 cm) partially embedded in the ice and with remnants of a fusion crust turned out to be the first martian meteorite recovered from Antarctica. Rounded and subhedral olivine grains apparently account for > 50 vol% of this heavily shocked meteorite, but like all shergottites, it contains significant amounts of pyroxene (~30 vol%) and maskelynite (~10 vol%). Pyroxene occurs as colorless prismatic crystals, sometimes twinned and sometimes enclosing olivine. Opaques (~2 vol%) include chromite, ilmenite, and traces of sulfides and, perhaps, meteoritic iron. Phosphates and other accessory phases are also reported. No obvious signs of weathering were evident upon first inspection, but a terrestrial age of ~ 200,000 years has been reported. Kaersutite provides prima facie evidence of preterrestrial aqueous activity and Raman spectroscopy evidence has also been used to adduce Martian aqueous alteration. It goes without saying that it requires very strong evidence to separate the effects of pre-terrestrial and post-terrestrial weathering. The reader is invited to read the literature for himself/herself.

There has been considerable discussion about the ages of the Shergottite meteorites, but most recent articles suggest that most or all of them were produced by lava flows of the past billion years. Many favor an age of less than 200 million years. A cosmic ray exposure age of ~3 Ma suggests that ALH 77005 may have been involved with several other shergottites in a preterrestrial collision either on Mars or as part of a large fragment from an earlier large ejection from Mars.

Approximately 80% of the 150+ recognized martian meteorites are classified as shergottites (Shergotty-like) as of June 2015. However, only 9 samples (representing 5 or more individual falls) were listed as "lherzolitic shergottites' at the Martian Meteorite Compendium which provides more specific classification data.

Bibliographical Note: The sources cited here are those most pertinent to establishing the mineralogy of ALH 77005. The Martian Meteorite Compendium provides a very detailed and more comprehensive bibliography for those interested.

Synonyms: ALH-77005 & ALHA77005 are two of several additional labels attached to this meteorite. More standardized abbreviations for Antarctic meteorites were developed later.

Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Allan_Hills_77005
Wikidata ID:	Q63434345

Other Regions, Features and Areas containing this locality

References