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    Published: May 12, 2011

    Field Museum Scientists Study Ancient Asteroid Impact

    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

     

    About 470 million years ago – in a time period called Ordovician – the parent asteroid of one of the L chondrites, one of the most common meteorite types, was disrupted in a collision with another body. This event led to a subsequent bombardment of Earth with collisional debris for at least 10 million years. This finding is reported in a recent study by Field Museum scientists Dr. Birger Schmitz (Research Associate), Robert A. Pritzker Assistant Curator of Meteoritics and Polar Studies Dr. Philipp Heck, and an international team of coauthors. Their paper was published in the journal Earth and Planetary Science Letters and focuses on rocks from the marine, 460 million year old 7-km-wide Swedish Lockne impact crater. Schmitz and his student isolated extraterrestrial minerals (chromites) from the crater rocks. Heck and colleagues used the electron and ion microprobes at the University of Wisconsin, Madison to analyze the elemental and oxygen isotopic composition of these chromites. Their analysis shows that the impactor was an ordinary (L) chondrite. A recent hypothesis by researchers from Berlin and Brussels that claims the impactor was an iron asteroid based on platinum group elements (PGE) in the crater can now be clearly rejected.  This is supported by PGE analyses by a collaborator at Woods Hole Oceanographic Institution, which shows that PGEs cannot identify the impactor type in this case. Noble gas analyses of the chromites performed by colleagues at ETH Zurich in Switzerland revealed that the grains traveled to Earth inside an asteroid and not as meteorites or micrometeorites.  The authors conclude that a fragment of the L chondrite parent body caused the impact.  The new study defines the period of increased bombardment of Earth with extraterrestrial material during the mid-Ordovician to at least 10 million years. The paper, “Determining the impactor of the Ordovician Lockne crater: Oxygen and neon isotopes in chromite versus sedimentary PGE signatures,” can be accessed at doi:10.1016/j.epsl.2011.04.028.

    Artist's impression of an asteroid impact into

    a shallow sea. Credit: Don Davis and NASA.

    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.