Meteorite 84001

 

Figure 1 Famous micrograph of Mars meteorite ALH84001 shows structures that resemble fossils, but most scientists regard them as mineral formations. Perseverance seeks less ambiguous evidence. NASA/JSC

Allan Hills 84001 (often abbreviated ALH84001) is a meteorite discovered by a team of US meteorite hunters from the ANSMET project on December 27, 1984, in Allan Hills, Antarctica. ALH84001, like the other SNCs (shergottite, nakhlite, and chassignite), is assumed to be from Mars. It does not, however, fit into any of the previously identified SNC groupings. It weighed 1.93 kilos when discovered (4.3 lb). It made headlines throughout the world in 1996 when scientists stated that carbonate globules found there might include evidence for minuscule remains of Martian microorganisms.

This rock is thought to be one of the Solar System's oldest parts, having crystallized from molten rock 4.091 billion years ago. It is considered to have evolved on Mars during a period when liquid water existed on the now barren planet's surface, according to chemical tests.

Vicky Hamilton of the University of Hawaii at Manoa presented data from the Mars Global Surveyor and Mars Odyssey spacecraft orbiting Mars in September 2005 to investigate the origin of ALH84001. The meteorite appears to have come from Eos Chasma in the Valles Marineris canyon, according to the research. The study was limited to areas of Mars that were not shrouded by dust, so it was inconclusive.

According to the scenario, ALH84001 was blasted off the surface of Mars by a meteorite collision 4.5 billion years ago and landed on Earth 13,000 years later. Radiometric dating techniques such as samarium-neodymium (Sm-Nd), rubidium-strontium (Rb-Sr), potassium-argon (K-Ar), and carbon-14 were used to determine these dates. Because they did not come from a "wet" Mars, other meteorites with probable biological marks have sparked less curiosity. ALH84001 is the lone meteorite discovered during this time frame.

Isotopic research revealed that the carbonates in ALH84001 were precipitated at a temperature of 18 °C with water and carbon dioxide from the Martian atmosphere, according to a paper published in October 2011. The carbonate carbon and oxygen isotope ratios indicate that the carbonates were deposited from a slowly evaporating subsurface water source, most likely a shallow aquifer a few meters or tens of meters beneath the surface.