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Published: March 16, 2011

Space Travel Time and Preatmospheric Size of Mifflin

Philipp Heck, Sr. Director, Negaunee Integrative Research Center; Robert A. Pritzker Curator for Meteoritics and Polar Studies; Head, Robert A. Pritzker Center, Negaunee Integrative Research Center

Right after the Mifflin Meteorite fell in SW Wisconsin in April 2010 the Robert A. Pritzker Assistant Curator of Meteoritics and Polar Studies Dr. Philipp R. Heck coordinated an international study to determine the time it spent in space and to calculate its size in space before it got ablated and broke apart in our atmosphere. Now, first results obtained from this study are published as extended abstracts, and were presented in more detail in March at the Lunar and Planetary Science Conference in Texas: The new results show that Mifflin was travelling through space as a small 3 feet object for about 20 Million years before it landed in Wisconsin.

Right after the Mifflin Meteorite fell in SW Wisconsin in April 2010 the Robert A. Pritzker Assistant Curator of Meteoritics and Polar Studies Dr. Philipp R. Heck coordinated an international study to determine the time it spent in space and to calculate its size in space before it got ablated and broke apart in our atmosphere. Now, first results obtained from this study are published as extended abstracts, and were presented in more detail in March at the Lunar and Planetary Science Conference in Texas: The new results show that Mifflin was travelling through space as a small 3 feet object for about 20 Million years before it landed in Wisconsin.

At the time of the meteorite fall Heck was visiting a lab in Europe and stayed in touch with the Robert A. Pritzker Center in Chicago by phone and e-mail. Collections manager for meteorites James L. Holstein sent out the meteorite as quickly as possible. “It is critical to do measurements as quickly as possible after the meteorite fall, because many of the radioactive elements that were produced in space, who are essential to measure, decay rapidly”, Heck says, “only thanks to the rapid donation of a large piece of Mifflin to us by private collector Mr. Terry Boudreaux, this study was possible.”

 

| Mifflin Meteorite |

The natural radioactivity from the meteorite is not harmful for humans and is in fact so low, that the measurement was done in a special laboratory shielded from other natural sources of radioactivity. The Gran Sasso National Laboratory is located deep beneath the Apennines Mountains in Italy. Collaborator Dr. Matthias Laubenstein was ready to do this high-sensitivity measurement right after the meteorite fall. Longer-lived radioactive elements were analyzed by collaborators Dr. Kees Welten at the University of California at Berkeley and Dr. Marc Caffee at Purdue University in West Lafayette, Indiana. Radioactive elements are produced when cosmic rays hit the meteorite in space. Their concentrations depend on the size of the meteorite in space and the results from the three different labs show that Mifflin was about 3 feet in diameter before it entered Earth’s atmosphere. This confirms the first size estimates from video footage of the fireball.

The same cosmic rays also produce stable elements in the meteorite such as the noble gases, neon and argon. The concentration of these noble gases and their production rates tell us how much time the meteorite spent in space – from its ejection from its parent asteroid to its fall on Earth – its interplanetary flight time or cosmic-ray exposure age. Matthias Meier, a graduate student at ETH Zurich in Switzerland analyzed a piece of a Field Museum’s Mifflin specimen with a noble gas mass spectrometer dedicated only for meteorites and determined its interplanetary flight time to be 20 million years. This is not unusual for this type of meteorite. He also found that Mifflin has not been shocked much by impacts since almost two billion years, and was only slightly affected by the large parent asteroid breakup event 470 million years ago. Dr. Heck, who is also a co-advisor of Meier, comments, "This is a good example that meteorites do not just sit around and ‘gather dust’ once they arrive at a natural history museum."

The results from this study are interesting on their own but also serve as puzzle pieces to improve our understanding of the evolution of the Solar System.

The public Mifflin Meteorite exhibit at the Field Museum (upper level, south) now features a beautiful cut slice of the meteorite which reveals the brecciated nature of the rock, signs of impacts on the parent asteroid in space. Numerous clasts and shiny specks of metal can be easily seen with the naked eye. Also new on exhibit is the piece of Mifflin found by an elementary school student on the Iowa-Grant school ground. Private meteorite collectors Terry Boudreaux and Michael Farmer each donated two pieces.

Read more about the “Cosmic-Ray Exposure History and Preatmospheric Size of the Mifflin L5 Chondrite Fall”.

Philipp Heck
Sr. Director, Negaunee Integrative Research Center; Robert A. Pritzker Curator for Meteoritics and Polar Studies; Head, Robert A. Pritzker Center

Philipp R. Heck serves as the Senior Director of Research at the Field Museum. Research at the Field Museum is conducted in the areas of Earth and Planetary Sciences, Life Sciences, Anthropology and Archeology, and is united in the Negaunee Integrative Research Center. Heck is the Robert A. Pritzker Curator of Meteoritics and Polar Studies at the Field Museum of Natural History in Chicago, IL in the Science & Education department and a Professor (part time) at the University of Chicago's Department of the Geophysical Sciences and the College (https://geosci.uchicago.edu/people/philipp-heck/). 

Heck's research focuses on presolar grains to understand our parent stars and the history of our Galaxy, early solar system materials, asteroids, and on the delivery history of extraterrestrial matter to Earth. For his research he studies the mineralogy and geochemistry of meteorites, micrometeorites and space-mission returned samples and also of fossil meteorites and micrometeorites found in Earth's sedimentary record. Heck joined the sample analysis team of NASA's OSIRIS-REx sample return mission. Heck was a member of the international research consortium to find and study the first modern interstellar dust returned by NASA's Stardust Mission. Heck is an executive committee member of the Extraterrestrial Materials Analysis Group (ExMAG) and is chairing the Microparticle Subcommittee.

As the curator in charge, Philipp R. Heck oversees the collection of meteorites at the recently established Robert A. Pritzker Center for Meteoritics and Polar Studies, the largest meteorite collection housed at a private institution with more than 12000 specimens and more than 1600 different meteorites. Other responsibilities include the curation of the gem, mineral, rock and economic geology collections.


Philipp R. Heck came to the Field Museum in March 2010 from the University of Chicago, where he was a postdoctoral scholar working on new analytical techniques for presolar grains. He obtained his M.Sc. and Ph.D. degrees at ETH Zurich in Switzerland in geo- and cosmochemistry. He then worked as a postdoctoral fellow at the Max-Planck-Institute for Chemistry where he studied the first comet dust brought back from Comet Wild-2 by NASA’s Stardust Mission and at the University of Wisconsin-Madison where he worked mainly on fossil meteorites and banded iron formations from around the world. For his studies he uses specialized analytical techniques such as secondary ion mass spectrometry (NanoSIMS, IMS-1280 and TOF-SIMS), noble gas mass spectrometry, atom probe tomography, scanning electron microscopy and electron microprobe analysis. Sample preparation for atom-probe work is performed with focused ion beam workstations.

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