Allan Hills 84001

Allan Hills 84001 (commonly abbreviated ALH84001) is a meteorite that was found in Allan Hills, Antarctica on December 27, 1984 by a team of U.S. meteorite hunters from the ANSMET project. Like other members of the group of SNCs (shergottite, nakhlite, chassignite), ALH84001 is thought to be from Mars. However, it does not fit into any of the previously discovered SNC groups. On discovery, its mass was 1.93 kilograms (4.3 lb). It made its way into headlines worldwide in 1996 when scientists announced that it might contain evidence for microscopic fossils of Martian bacteria based on carbonate globules observed.

History and description

This rock is considered to be one of the oldest pieces of the Solar System, proposed to have crystallized from molten rock 4.091 billion years ago. Based on chemical analyses, it is thought to have originated on Mars from a period when liquid water existed on the now barren planet's surface.

In September 2005, Vicky Hamilton of the University of Hawaii at Manoa presented an analysis of the origin of ALH84001 using data from the Mars Global Surveyor and Mars Odyssey spacecraft orbiting Mars. According to the analysis, Eos Chasma in the Valles Marineris canyon appears to be the source of the meteorite. The analysis was not conclusive, in part because it was limited to areas of Mars not obscured by dust.

Aluminium hydride

Aluminium hydride (also known as alane) is an inorganic compound with the formula AlH₃. It is a colourless pyrophoric solid. Although rarely encountered outside of research laboratories, alane and its derivatives are used as reducing agents in organic synthesis.

Structure

Alane is a polymer. Its formula is sometimes represented with the formula (AlH₃)_n. Aluminium hydride forms numerous polymorphs, which are named α-alane, α’-alane, β-alane, δ-alane, ε-alane, θ-alane, and γ-alane. α-Alane has a cubic or rhombohedral morphology, whereas α’-alane forms needle like crystals and γ-alane forms a bundle of fused needles. Alane is soluble in THF and ether, and its precipitation rate from ether depends on the preparation method.
The structure of α-alane has been determined and features aluminium atoms surrounded by 6 hydrogen atoms that bridge to 6 other aluminium atoms. The Al-H distances are all equivalent (172pm) and the Al-H-Al angle is 141°.

α-Alane is the most thermally stable polymorph. β-alane and γ-alane are produced together, and convert to α-alane upon heating. δ, ε, and θ-alane are produced in different crystallization condition. Although they are less thermally stable, they do not convert into α-alane upon heating.

Allan Hills A81005

Allan Hills A81005 or ALH A81005 (sometimes also named without the "A" in front of the number) was the first lunar meteorite found on Earth. It was found in 1982 in the Allan Hills at the end of the Transantarctic Mountains, during a meteorite gathering expedition (ANSMET).

Discovery and naming

ALH A81005 was found on 17 January 1982 by John Schutt and Ian Whillans. It is named after the Allan Hills, a mountain chain in Antarctica where many meteorites are gathered by expeditions. The large number of meteorites collected in Antarctica and the lack of geographic terms that could be used for names have led to the adaption of the "Antarctic rules" for meteorite naming. Every meteorite found in Antarctica receives the names of the collection area (Allan Hills) and a number. The number consists of the year the expedition started "81" and a three digit number that is given out consecutively (005). The "A" in front of the number stands for meteorites collected by ANSMET expeditions and can be considered optional. The definition of the year is used because the year changes during the Austral summer season (December to March) and this avoids samples from one expedition having different years. This is the reason ALH A81005 has the year "81" in its name despite being found on 17 January 1982.