A Martian meteorite is a piece of rock that has been ejected from Mars via meteoritic impact or volcanic eruption and travels through space then lands on Earth.
Many different classifications of meteorites exist, each with a distinct composition of elements. A meteorite tells the geologic history of the body it originates from. Several classifications of Martian meteorites exist, the basic categories are: shergottites, nakhlites, chassignites (collectively known as SNC meteorites), and OPX (orthopyroxene) Martian meteorites. Each category has sub groups and crossovers and exceptions occur. The classification of shergottites contains rocks that are found to be basaltic to igneous. This classification gets its name from a meteorite that fell in 1865 in the town of Shergotty, India. Nakhlites are formed by an accumulation of crystals. Subgroups of nakhlites include clinopyroxenites and wehrlites. The classification chassignites were named after a group of cumulate meteorites that were discovered in Chassigny, France in 1815. OPX Martian meteorites are a smaller group rich in orthopyroxene. (ISMP 2013)
The estimates vary greatly for the amount of material that falls to the Earth each year. Some scientists estimate that 37,000 to 87,000 tons of material falls to Earth annually, but of that only 4-5 tons are big enough to land and be collected. However, finding them takes time and patience. Meteorites could conceivably come from anywhere in the solar system. However, of particular interest to scientists are meteorites from Mars. Meteorites are studied extensively by astrobiologists for the purpose of finding organic compounds, amino acids, and possibly life forms. An estimated 250-300 pounds of known Martian meteorite material is in the possession of scientists on Earth. Meteorites can be found anywhere, but some places make them easier to find such as desert regions and Antarctica. The contrast of the light sand or white snow and the dark colored meteorites allows scientists to see the meteorites. (Willett 2013) Meteorite ALH 84001 was discovered in 1984 in a region of Antarctica called Allen Hills. The classification for this rock is an OPX. This category is made up of achondrite meteorites which are a rocks that do not contain round chondrate spherules. An orthopyroxenite(OPX) is a rock made of orthopyroxene and pyroxenite. ALH 84001 has gotten more attention than any other in recent history. (ISMP ALH 84001 2013) The Allen Hills meteorite was studied by Dr. David McKay of NASA. He published an article in the Journal Science in 1996 that claimed meteorite ALH 84001 contained microfossils. This sent shockwaves through the scientific community and the world media. Dr. McKay used scanning electron microscope (SEM) technology to image very fine slices of the meteorite. When he saw the images he and his team determined that they were microfossils of bacteria that had been preserved in the meteorite from Mars, thus concluding there had been life on the Red Planet in the past and may still exist there now. Immediately other scientists started examining the evidence and some of them came to the conclusion that the results were an artifact of the SEM process and not life. (NASA 2009) Others stand by McKay’s results and have helped to continue his research. Journal articles supporting and debunking the results are published on a regular basis. The objects inside the Allen Hills meteorite may never be proven to be microfossils. However, with the exponential increase of technological advancements we can use other meteorites to supplement the data we find to determine what the potential for life is on Mars and in our Solar System.
The Sahara Desert in Africa is where a headline grabbing meteorite was found. This meteorite dubbed NWA 7034 has been found to be a 2.1 billion year old volcanic meteorite from Mars. It is given its own classification called basaltic breccias. (ISMP 2013) This was determined by examining the chemical signature of the object. It is nicknamed “Black Beauty” because it has a beautiful dark sheen on its surface. It is said to have been part of a Martian volcanic eruption that sent it off the planet’s surface or by a large meteorite that struck the surface of Mars with enough force to send the rock into the solar system, where it travelled for a couple of billion years until it landed in Africa. When the meteorite was examined it gave off a small amount of water vapor, but compared to other Martian meteorites Black Beauty contained much more water. It also appears to have been altered by an interaction with surface or ground water on the surface of the Red Planet. The fleet of spacecraft sent to Mars have confirmed several times over that Mars once had water on the surface and according to NASA may still have periodic outflows of surface water. (ISMP NWA 7034 2013) Scientists are excited because, while they vacillate a Mars Sample Return Mission, they now have another piece of Mars that they can hold in their hands and study here on Earth. NASA scientists have stated that this is the richest geochemical meteorite found to date.
Falling near Murchison Australia in 1969, the Murchison meteorite was witnessed falling to the ground. It is one of the most studied meteorites in the world. It is not thought to have originated from Mars, but the scientific findings of this space rock pose many questions for scientists, especially astrobiologists. This meteorite has been found to contain many amino acids. Some studies say 15 others say 20 or more. (ISMP 2013 Murchison) An amino acid is an organic compound. It is a three part grouping of nucleotide base pairs. These amino acids make up proteins and they encode genes which then make up a DNA strand. (Kvenvolden et al. 1970) To better understand the significance of the amino acid discovery, imagine a nucleotide base as a letter in the alphabet, then group three together to make an amino acid which is like a word in a sentence, next a protein is analogous to a sentence, a gene is like a chapter in a book, and the DNA strand is like an entire book telling the story of an organism. Although the Murchison meteorite is not from Mars, it begs the question, if there are amino acids in meteorites falling from the sky onto Earth, then why wouldn’t there be meteorites falling to Mars with the same organic material? NASA’s Dr. John Grotzinger explained that the organic compounds recently discovered by the Curiosity Rover may not have originated from Mars. It should not matter where the organic material came from. The organic compounds are there now. Of course this excludes contamination from Earth. Everything on every planet came from somewhere else. We are a collection of material that came from the same swirling cloud of gas and dust. So if organic compounds are on one planet or satellite, then it is logical that all of the bodies in the solar system, and therefore galaxy, have the same ingredients for life. This has also been confirmed by spacecraft that have taken samples from cometary debris which also had amino acids in them. (Rietmeijer 2010)
List of Martian meteorites.
International Society for Meteoritic and Planetary Science (ISMP). 2013. “Recommended Classifications.” Accessed December 29, 2013. http://www.lpi.usra.edu/meteor/metbullclass.php?sea=Martian+%28OPX%29 (ISMP 2013)
Willett, Nicole. 2013. “Mars and Meteorites (Issue #10).” Red Planet Pen, October 27, 2013. http://education2.marssociety.org/mars-and-meteorites-issue-10/ (Willett 2013)
International Society for Meteoritic and Planetary Science (ISMP ALH 84001). 2013. “Allen Hills 84001.” Accessed December 29, 2013. http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&valids=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&rect=&phot=&snew=0&pnt=Normal table&code=604. (ISMP ALH 84001 2013)
NASA. 2009. “New Study Adds to Finding of Ancient Life Signs in Mars Meteorite.” Accessed December 29, 2013. http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html. (NASA 2009)
International Society for Meteoritic and Planetary Science (ISMP NWA 7034). 2013. Accessed December 29, 2013. http://www.lpi.usra.edu/meteor/metbull.php?sea=nwa+7034&sfor=names&ants=&falls=&valids=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&rect=&phot=&snew=0&pnt=Normal table&code=54831. (ISMP NWA 7034 2013)
International Society for Meteoritic and Planetary Science. 2013. Accessed December 29, 2013. http://www.lpi.usra.edu/meteor/metbull.php?sea=murchison&sfor=names&ants=&falls=&valids=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&rect=&phot=&snew=0&pnt=Normal table&code=16875 (ISMP Murchison 2013)
Kvenvolden, Keith and Lawless, James and Pering, Peterson, Etta and Flores, Jose and Ponnamperuma, Cyril and Kaplan I.R., Moore, Carleton. 1970. “Evidence for Extraterrestrial Amino-acids and Hydrocarbons in the Murchison Meteorite.” Nature. 228:923-26 Accessed December 29, 2013. doi:10.1038/228923a0 (Kvenvolden et al. 1970)
Rietmeijer, Frans J.M. 2010. “Stardust glass: Indigenous and modified comet Wild 2 particles.” Meteoritics and Planetary Science. 44: 1707-15. Accessed December 29, 2013. doi: 10.1111/j.1945- (Rietmeijer 2010)