Allan Hills 84001
ALH 84001 (Allan Hills 84001) is a meteorite found in Allan 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), ALH 84001 is thought to be from Mars. On discovery, its mass was 1.93 kg.
History
This rock is theorized to be one of the oldest pieces of the solar system, proposed to have 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 and is related to other martian meteorites. The theory holds that it was shocked and broken by one or more meteorite impacts on the surface of Mars some 3.9 to 4.0 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.[1][2]
Possible lifeforms
On August 6, 1996[3] 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 and Richard Zare of Stanford University.[4][5]
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 ALH 84001 are 20-100 nanometres in diameter, similar in size to the theoretical nanobacteria, but smaller than any proven cellular life[citation needed]. 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 contamination.
The announcement of possible extraterrestrial life caused considerable controversy 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.[6]
Several tests for organic material have been performed on the meteorite and amino acids and polycyclic aromatic hydrocarbons (PAH) have been found. The debate if the organic molecules were created by nonbiological processes or are due to contamination from the contact with Antarctic ice is still on going.[7][8]
As of 2006 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 the features were formed, but similar features have been recreated in labs without biological inputs.[3] According to the Associated Press, "skeptics have found non-biological explanations for every piece of evidence that was presented on Aug. 6, 1996. And though they still vigorously defend their claim, the NASA scientists who advanced it now stand alone in their belief."[3]
Recent studies on ALH 84001 have shown that, although chances are low, eventually, Martian rocks such as ALH 84001 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.[citation needed] 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.
If Mars's atmosphere at the time life started on Earth was like it is now, though, survival and propagation after arriving would be even less likely. Its native environment probably would be completely unlike anywhere it would land on Earth, much like for a deep sea fish suddenly arriving in the middle of the Sahara desert. Mars has an atmosphere many times thinner than that on top of Mount Everest, with almost no water. A life form evolved to survive in such conditions would almost invariably find dense air to be toxic, as it would the relatively high temperatures[citation needed]: even the Antarctic does not get as cold as much of Mars does much of the year. However, it is hypothesized that ALH 84001 originated from a time period during which water may have existed on Mars.[3] Also, Earth's atmosphere at that time was largely anoxic, i.e., without oxygen. Other meteorites that have what may be biological markings have generated less interest because they do not originate from a "wet" Mars. ALH 84001 is the only meteorite collected from such a time period.[3]
Origin on Mars
In September 2005, Vicky Hamilton of the University of Hawaii at Manoa presented an analysis of the origin of ALH 84001 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.[9] The analysis was not conclusive, in part because it was limited to parts of Mars not obscured by dust.
ALH 84001 in fiction
- Deception Point, a novel by Dan Brown, refers to the ALH 84001 meteorite in its central theme.
- Contact, a 1997 film adaptation of the novel by Carl Sagan, contains footage of President Bill Clinton commenting on the discovery of the possible Martian fossils. This footage was taken out of context so as to be incorporated in the film. It reportedly garnered some minor criticism from individuals in the Clinton administration.[citation needed]
See also
- Martian meteorite
- Life on Mars
- Panspermia, or more correctly Exogenesis
References
- ^ 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.
- ^ a b c d e Crenson, Matt (2006-08-06). "After 10 years, few believe life on Mars". Associated Press (on space.com. Retrieved 2006-08-06.
{{cite web}}: Check date values in:|date=(help); External link in|publisher= - ^ 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.
- ^ McKay D. S., Gibson E. K., ThomasKeprta K. L., Vali H., Romanek C. S., Clemett S. J., Chillier X. D. F., Maechling C. R., Zare R. N. (1996). "Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001". Science. 273: 924–930.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Clinton, Bill (1996-08-07). "President Clinton Statement Regarding Mars Meteorite Discovery". NASA. Retrieved 2006-08-07.
{{cite web}}: Check date values in:|date=(help) - ^ Bada J. L., Glavin D. P., McDonald G. D., Becker L. "A search for endogenous amino acids in martian meteorite ALH 84001". Science (279): 1998.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Becker L., Glavin D. P., Bada J. L. (1997). "Polycyclic aromatic hydrocarbons (PAHs) in Antarctic Martian meteorites, carbonaceous chondrites, and polar ice". Geochimica et Cosmochimica Acta. 61: 475–481.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Birthplace of famous Mars meteorite pinpointed. New Scientist article. URL accessed March 18, 2006.
- Mittlefehldt D. W. (1994) "ALH84001, a cumulate orthopyroxenite member of the SNC meteorite group". Meteoritics, 29, 214-221. URL accessed March 18, 2006.
- Stephan T., Jessberger E. K., Heiss C. H. and Rost D. (2003) "TOF-SIMS analysis of polycyclic aromatic hydrocarbons in Allan Hills 84001". Meteorit. Planet. Sci. 38, 109–116.