Today is one of those days where its hard for me to choose a topic. A lot of things happened on August 6: members of the Constitutional Convention received copies of the first real draft of the US Constitution to debate and edit; the US used Little Boy to obliterate Hiroshima; LBJ signed the Voting Rights Act of 1965; Alfred, Lord Tennyson and Alexander Fleming and Lucille Ball and Andy Warhol were born; Harry Reasoner and Rick James and Marvin Hamlisch died... But for today, Ive decide to get a little bit spacey... On this date (August 6) in the year 1996, NASA announced that the ALH 84001 meteorite (a space rock thats believed to have come from Mars) contains internal structures that might be evidence of primitive life. In December 1984, a team of US meteorite hunters found this particular rock in Allan Hills, Antarctica. Certain specific properties of this chunk o space rock place it in a category called SNC. I wont get too geeky on you, but the SNC group are meteorites that came from Mars. For those of you who are wondering how rocks from other planets end up on Earth, the answer is actually quite simple. One of the most popular pastimes among Martians is the famed Martian Rock Fight - they throw rocks at each other, and get points based on where the rocks hit. For example, they get 10 points for hits on either torso, and 50 points if they can score a hit on the middle of their 3 heads. As it turns out, Martians are super-strong, so when they miss each other, the rocks go sailing off into space - and gravity brings some of them to Earth. I am giggling to myself as I picture the wide gamut of reactions the previous paragraph caused... Actually, the cause is much simpler... when asteroids or comets or other meteorites strike the surface of a planet, debris is ejected into space where it drifts for millions, or even billions of years. Some of that debris eventually drifts our way and gets caught in our gravitational field. The vast majority of that debris burns up in our atmosphere, but some of the bigger chunks make it through - and those are meteorites. By analyzing the composition of those chunks, and comparing them to what we know of the other planets in our solar system, asteroids, comets, and other space stuff, we can tell where the meteorites came from. Mars is particularly easy, because we know so much about it, now that weve had landers and rovers and labs on the surface for so long. Scientists have captured and cataloged almost 65,000 meteorites... as of March 2014, 132 of them have been identified as Martian - including ALH 84001. Because of all of the equipment we have on the surface and in orbit around Mars, we actually know quite a bit about this meteorite. Chemical composition tests suggest that the rock came from the area around Eos Chasma in the Valles Marineris canyon. Current findings show that the rock was ejected from the surface of Mars by an impact some 4.5 billion years ago, and fell to Earth around 13,000 years ago. (For those who love geeking as much as I do, scientists arrived at the former date via Sm-Nd, Rb-Sr, and K-Ar dating, and the latter date by C-14 dating.) This dating was exciting to scientists - not because of any stereotypical geeks cant get dates hilarity (there are lots of scientists who get dates!) - but because ALH 84001 was the only Martian meteorite we had at that point that came from Mars while liquid water still existed on its surface. Isotopic analyses suggest that the carbonates in the meteorite were precipitated at around 18°C - and the carbonate and oxygen isotope ratios imply deposition of the carbonates from a gradually evaporating subsurface water body, probably a shallow aquifer a few meters below the surface. Yeah, thats geeky, but it is exciting because life (at least as we currently understand it) requires liquid water. Once these researchers made those discoveries, they immediately looked at the rock under the most powerful electron microscopes available. And on August 6, 1996, NASA published an article in Science where they discussed their findings. Chain structures within the meteorite, measuring between 20 and 100 nanometers in diameter, resemble smaller versions of terrestrial fossilized nanobacteria. The announcement made headlines all over the world - including a formal televised announcement by President Clinton. Since then, more Martian meteorites have been found from that time period, all of which have similar structures within the rock. Unfortunately, the life on Mars question has still not been completely validated. In theory, the question should be easy enough to answer - but in practice, we still dont have sufficiently powerful high-resolution 3D scans to establish the morphology and physiology required to definitely declare these structures as actual fossilized life. But you know they are working on it. As our technology improves, were bound to find something... So today is the 18th anniversary of the announcement that weve found Martian life in an ancient meteorite. The whole are we alone question still rattles a lot of cages. Lots of folks are thrilled by the idea. Im psyched that were less than 50 years from Zefram Cochranes warp drive flight that puts us in touch with the Vulcans. On the other side of the fence, there are folks who dont even want to think about it. The foil-hat club is worried about probing where the sun dont shine. Professional un-rocket-scientist Ken Ham wants to defund NASA in order to build more creationist museums because if there are aliens, theyre going to hell. Ken Hams exact polar opposite, Stephen Hawking, warned us to be careful, reminding us that if aliens ever visit us, I think the outcome would be much as when Christoper Columbus first landed in America, which didnt turn out very well for the Native Americans. Fair point, Professor! Still, the idea of extraterrestrial life has been a part of human shared consciousness for a very long time. Less than 20 years ago, we mightve found something that points us in that direction. Just a couple of weeks ago, scientists at NASA suggested that we might find actual evidence of alien life within the next 20 years. Scary, spooky, exciting, mind-blowing... whatever happens will happen - and we have really good seats for the show!
Posted on: Wed, 06 Aug 2014 16:12:29 +0000
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