Antarctic Meteorites

1. Antarctic Meteorites Molly Reardon ES 567 Final Project Spring 2010 http://www.emporia.edu/earthsci/ amber/go340/students/reardon/

2. Project Presentation Overview I am a graduate student at Emporia State University in Earth Science. This project was for my gemstone course, www.emporia.edu/earthsci/amber/go340, and includes: • Introduction • Historic review • Meteorite concentration mechanism & areas • Collecting methods • Shipping & analysis • Origins • Classification • Conclusions & references For comments or questions, mreardon@emporia.edu

3. Introduction • Meteorites are rock and gemstones too! There is not one generally accepted definition for “gemstone”, however, they all have something unique about them. In the case of meteorites, their origin is what sets them apart from other gems we’ve studied in this course.

4. Introduction • What is a meteorite? - It’s a fragment of a space rock that lands on Earth as the result of a collision or impact between two parent rocks. - Some have lunar or Martian origins, but most originate from the asteroid belt. - Meteoritic events that are witnessed are called a “fall”, while meteorites that are stumbled upon are called a “find.” - Meteorites are usually named after the person who discovered them or after the closest town or geographic landmark.

5. Introduction • Why are Antarctic Meteorites significant? - More meteorites have been found here than on any other continent. - A special concentrate mechanism exists to explain why so many different meteorites are found on the ice. - Antarctica is an amazing place to talk about and study!

6. Antarctic Search for Meteorites (ANSMET) - In the early 1970’s, at a Meteoritical Society meeting, http://www.meteoriticalsociety.org/, Japanese scientists described finds of 9 different kinds of meteorites in one area in Northeastern Antarctica. - Until this point, meteorites concentrated in one location have always been from the same fall. - Meteorites found on the ice by expeditions dating back to 1911 were not realized to be significant. It was unknown these rocks were parts of much larger “strewn fields”. • American scientist, William Cassady recognized the significance of the Japanese find and conducted more research. Eventually his proposals were accepted by the National Science Foundation and he founded the ANSMET program.

7. The Concentration Mechanism - Thousands of years ago, meteorites fell to earth and became embedded in the Antarctic Ice. - As the glacial ice flowed downstream from the interior of the continent to the coastal regions, it carried embedded rocks and debris with it. - Sometimes the ice encounters a barrier or stagnation point, such as a mountain range or a subsurface ridge. When ice stops flowing at stagnation points, it evaporates or ablate. - The rocks and debris embedded in the ice at these stagnation points will gradually make their way to the surface as the ice they are contained in ablates. - We are then left with a concentration of rocks in one location; most of which come from varying sources and started their downward journey at different times. (See image on next slide)

8. The Concentration Mechanism (con’t) • Image depicts the concentration mechanism responsible for meteorite strewn fields on the Antarctic Continent. • Image obtained from: http://curator.jsc.nasa.gov/antmet/index.cfm

9. Concentration Areas • The image to the right shows known concentration fields along the Western edge of the Transantarctic Mountains. • The Transantarctic Mountains act as a barrier to the ice that is flowing from the interior of the continent (North East) to the coastal areas (South West). • The region depicted on the map is the predominant area of study for the ANSMET program. • Image obtained from: http://meteorites.wustl.edu/lunar/ • ansmet_locations.htm N

10. Collection - To determine potential collection points and concentration areas, ANSMET scientists study the US Geologic Survey's archive of aerial and satellite photos of Antarctica in Reston, Virginia. - They are specifically looking for direction of ice flow marked by crevasse fields and potential boundaries such as mountains and subsurface ice ridges. • These areas are distinguishable on satellite and aerial photos by variations in pattern and color of the ice.

11. Collection (con’t) - Once on the ice, the scientists branch out to potential areas of interest and set up a field camp. - The field seasons occur during the Austral Summer, between October and February of each year. The climate is too harsh to be outdoors during the winter months. Summertime temps can range from -55F up to 0F. Summertime has the added benefit of 24/7 sunlight. So scientists can work round the clock! • Image right shows typical field camp occupied by ANSMET participants. Image obtained from: • geology.cwru.edu/ • ~ansmet/living/index.html

12. Collection (con’t) - Depending on location, meteorite searches conducted on foot or skidoo. - Skidoos used to cover large areas of open ice where only a few rocks are present. - On-foot searches conducted in glacial moraines where many rocks are present, and distinguishing between earth rocks and meteorites requires a closer look. A typical method is 5-6 people to be spread out over 30-40 meters and to search ground in a series of sweeps. Image obtained from: http://geology.cwru.edu/ ~ansmet/collecting/index.html

13. Collection (con’t) - If a rock is suspected to be a meteorite, it is put into collection kit - The kit contains “sterile bags to put the meteorites in, numbered tags to label them with, tape to close and seal the bags, a notebook to take down any distinguishing features of the sample, and some scissors to cut the tape.” (http://geology.cwru.edu/~ansmet/collecting/index.html) This image obtained from: http://geology.cwru.edu/ ~ansmet/collecting/index.html

14. Shipment and Analysis - Once the rocks are collected from the ice, the shipment processes begins. - The rocks are kept frozen and packaged into coolers that are shipped to the Antarctic Meteorite Curation labs at the Johnson Space Center (JSC) in Houston, Texas - At the labs, the rocks are carefully thawed and cracked open for study. - The JSC classifies and assigns a name and number to the rock. Then they write a short description which is published in the Bi-Annual Antarctic Meteorite Newsletter, found here: http://www-curator.jsc.nasa.gov/antmet/amn/amn.cfm

15. Origins • The JSC classifies meteorites based on composition. • There are three main origins of meteorites found on earth: - Lunar - Martian - Asteroid Belt

16. Origins (con’t) • Lunar - A lunar meteorite is “a rock found on earth that was “ejected from the Moon by the impact of an asteroidal meteoroid or possibly a comet. ” (http://meteorites.wustl.edu/lunar/moon_meteorites.htm) - By testing suspected meteorites for chemical compositions, isotope ratios, minerals, and textures, comparisons can be made to moon rocks collected on Apollo missions. - Lunar meteorites found on Earth contain a fusion crust which is evident on the outside of the rock. This crust formed with deceleration through Earth’s atmosphere. • One example of using chemical composition to determine origins of the rock is with the lunar meteorites that are classified as “feldspathic breccias.” These rocks are rich in aluminum and calcium which is indicative of the mineral anorthite. The lunar highlands area is composed of this mineral, which is not known to be present on other planets or our asteroid belt.

17. Origins (con’t) • This is a lunar meteorite found in the MacAlpine Hills area of Antarctica in 1989. • The cube in the lower left is 1cm X 1cm. Note the fusion crust on the outside of the rock. Image obtained from: http://meteorites.wustl.edu/ lunar/moon_meteorites.htm

18. Origins (con’t) • Martian - A Martian meteorite is a rock that originated on Mars and as the result of some sort of celestial impact, has been ejected into the solar system and landed on Earth. - Of the tens of thousands of meteorites that have been found on Earth, only a small fraction (less than 40) have been identified as originating from Mars. • The isotope ratios in the Martian rocks are what typically separates these meteorites from other Earthly rocks. • A previously unknown type of martian meteorite was discovered by ANSMET scientists in 2003. For more info, see: www1.nasa.gov/home/hqnews/2004/jul/HQ_04232_meteorite.html

19. Origins (con’t) • The Martian rock below was discovered in the Allan Hills area of Antarctica in 1977. Through isotope ratio testing and examining the igneous interior, this was determined to be a Martian sample. Cube in lower right is 1cm X 1cm. • Image obtained from: • http://www2.jpl.nasa.gov/ • snc/alha1.gif

20. Origins (con’t) • Asteroid Belt - Asteroids are small planetary bodies that orbit our sun within the asteroid belt and pass between Jupiter and Mars. Occasionally, asteroids collide and rock remnants from the impact get pulled into the Earth’s atmosphere and fall to the ground. - Meteorites with asteroid belt origins are the most common type found on Earth. - The chemical composition of meteorites from the asteroid belt fall into one of three categories: Carbonoceous, Silicates, and Metallics. The presence of a fusion crust and chemical composition are what sets asteroid belt meteorites apart from Earthly rocks.

21. Origins (con’t) • This is a typical rock from the asteroid belt. Dimensions are approx 5cm X 5cm. This is a stone meteorite classified as a chondrite (see next slide), and does contain trace amounts of nickel iron. Image obtained from : http://curator.jsc.nasa.gov/ antmet/amn/AMNJul97/ PetDes.htm#GRO95551

22. Classification • Meteorites are classified into three main groups - Irons - Stony Irons - Stone

23. Classification (con’t) • Irons - Irons originate in the differentiated core of a planetary body and have extremely high densities. - They contain varying amounts of nickel-iron masses. - They are subdivided into three groups hexahedrites, octahedrites, and ataxites which are differentiated by the amount of nickel in each.

24. Classification (con’t) • Iron Octahedrite: Octahedrites contain 6.5% – 13% nickel. Image right obtained from http://curator.jsc.nasa.gov/antmet/amn/ AMNAug96/PetDes.htm#GRO95522 The tiny cube in lower right is 1cm X 1cm • Iron Hexadedrite: A type of iron meteorite made entirely of • kamacite (a nickel-iron alloy) and named for its cubic • (hexahedral) crystal structure. Contains 4.5% - 6.5 % nickel • Iron Ataxites: Made almost entirely of taenite (a • nickel-iron alloy) with a loose chemical structure. • Contains 16% - 30% nickel

25. Classification (con’t) • Stony Irons • These rocks are a combination of mantle-rock and nickel iron that have been fused together by impact. • Stony Irons contain two subgroups called mesosiderites and pallasites.

26. Classification (con’t) Mesosiderites: contain equal parts of metallic nickel-iron and silicate. Image obtained from: http://curator.jsc.nasa.gov/antmet/ samples/petdes.cfm?sample=ALHA81208 Pallasites: contain olivine crystals of peridot quality in an iron-nickel matrix. You can see the olivine suspended in the iron-nickel in this image. Image obtained from: http://curator.jsc.nasa.gov/antmet/ samples/petdes.cfm?sample= ALHA81208

27. Classification (con’t) • Stones - These rocks are the most abundant type of meteorite found. They have been known to come from the Moon, Mars, and the asteroid belt. - These rocks are suspected to have formed 4.56 billion years ago, after the formation of the sun. - Stone meteorites consist of two subgroups: chondrites and achondrites.

28. Classification (con’t) • Chondrites: contain "chondrules," which are gaseous inclusions that formed during the solar nebula. This image is a close-up under polarized light of an ordinary chondrite. You can see the gaseous chondrule inclusions in the rock. Image obtained from: http://curator.jsc. nasa.gov/antmet/samples/petdes.cfm?sample=ALH82110 • Achondrites: This is a stone meteorite that contains no chondrules. Image is a close up of a Martian Achondrite found on Antarctica. Image obtained here: http://curator.jsc.nasa.gov/antmet/ samples/petdes.cfm?sample= ALHA77005

29. Conclusion - Although meteorites are not typically associated with aesthetically pleasing gemstones, they are being cut and fashioned using the cabochon style. Their unique origins set them apart from other gems with the exception of moldavite! - Meteorites provide a glimpse into planetary geology and the possible formation of our solar system. These gemstones are extremely valuable for their geologic significance. • Because of the concentration mechanism on the Antarctic Ice and the proven success of meteorite finds, it’s imperative that this research continues and that some specimens are preserved as gems!

30. Resources • www.antarcticconnection.com/antarctic/science/meteorites.shtml • geology.cwru.edu/~ansmet/ • www-curator.jsc.nasa.gov/antmet/index.cfm • www-curator.jsc.nasa.gov/antmet/amn/amn.cfm • www.gi.alaska.edu/ScienceForum/ASF7/744.html • nineplanets.org/meteorites.html • www.emporia.edu/earthsci/amber/go340/syllabus.htm • www.bwsmigel.info/GEOL.115.ESSAYS/Gemology.Meteorites.html • wapi.isu.edu/geo_pgt/Mod05_Meteorites_Ast/mod5.htm • Cassady, W. A. 2003. Meteorites, Ice, and Antarctica. Cambridge University Press.