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ALH84001 (Allen Hills, 1984 #001) is a meteorite found in Allen Hills, Antarctica in December 1984 by a team of US meteorite hunters from the ANSMET project. Like other members of the group of SNCs (shergottite, nakhlite, chassignite), ALH84001 is thought to be from Mars. On discovery, its weight was 1.93 kg.

History

This rock is one of the oldest known pieces of the solar system, having crystallized from molten rock 4.5 billion years ago. Based on hypotheses surrounding attempts to identify from whence extraterrestrial rocks come, it is supposed to have originated on Mars. Theoretically, it was shocked and broken by one or more meteorite impacts on the surface of Mars some 3.6 billion years ago, but remained on the planet. It was later blasted off from the surface in a separate impact about 15 million years ago. Following some interplanetary travel, impacted Earth roughly 13,000 years ago. These dates were established by a variety of radiometric dating techniques, including samarium-neodymium (Sm-Nd), rubidium-strontium (Rb-Sr), potassium-argon (K-Ar), and carbon-14.Nyquist, L. E.; Wiesmann, H.; Shih, C.-Y.; Dasch, J. (1999) "Lunar Meteorites and the Lunar Crustal SR and Nd Isotopic Compositions" (PDF). Lunar and Planetary Science, volume 27, page 971. URL accessed March 18, 2006.Borg, Lars. E, et al (1999) "The Age of the Carbonates in Martian Meteorite ALH84001". Science, Vol. 286. no. 5437, pp. 90 - 94. URL accessed March 18, 2006.

Possible lifeforms

In 1996 ALH 84001 became newsworthy when it was announced that it was believed that the meteorite contained traces of life from Mars, as published in an article in Science by Dr. David McKay of NASA McKay, David S., et al (1996) "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001". Science, Vol. 273. no. 5277, pp. 924 - 930. URL accessed March 18, 2006..

Under the scanning electron microscope structures were revealed that for some time were considered to be the remains—in the form of fossils—of bacteria-like lifeforms. The structures found on ALH84001 are 20-100 nanometres in diameters, similar in size to the theoretical nanobacteria, but smaller than any proven cellular life. If the structures are really fossilized lifeforms, they would be the first solid evidence of the existence of extraterrestrial life, aside from the chance of their origin being terrestrial contaimination.

This caused a considerable stir at the time and opened up interest in Martian exploration. When the discovery was announced, many immediately conjectured that the fossils were the first true evidence of extraterrestrial life—making headlines around the world, and even prompting U.S. President Bill Clinton to make a formal televised announcement to mark the event.

As of 2005 however, most experts agree that the microfossils are not indicative of life, but of contamination by earthly biofilms. It has not yet conclusively been shown how they formed.

Recent studies on ALH84001 have shown that, although chances are low, eventually, Martian rocks such as ALH84001 could actually transfer Martian life to earth. 1 in 10 million meteorites from Mars arrives in less than a year, and around 10 rocks that weigh more than 100 grams make the journey in 2-3 years. Bacterial spores, and rock dwelling organisms are speculated to survive in space for 5 years, meaning transfer of Martian life to our planet is entirely possible.

Survival and propagation after arriving, though, would be even less likely. Its native environment is completely unlike anywhere it would land on Earth, as if a deep sea fish suddenly arrived in the middle of the Sahara desert. Mars has an atmosphere thinner than that on top of Mount Everest, with almost no oxygen or water. A life form evolved to survive in such conditions would almost invariably find oxygen, water, and dense air to be toxic, as it would the relatively high temperatures: the antarctic does not get as cold as much of Mars does much of the year.

Origin on Mars

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 Birthplace of famous Mars meteorite pinpointed. New Scientist article. URL accessed March 18, 2006.. The analysis was not conclusive, in part because it was limited to parts of Mars not obscured by dust.

See also

References

External links

Meteorites | Mars

ALH84001 | ALH84001 | ALH84001 | ALH84001 | ALH84001 meteorit | アラン・ヒルズ84001 | Meteorito ALH84001

 

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