Field Museum studies rare meteorite possibly from the outer asteroid belt

On April 22, 2012 a very fast-moving fireball was observed over large parts of California and Nevada. Equivalent to four kilotons of TNT, the fireball was photographed, and recorded by video and by weather Doppler-radars. The photographs and videos helped to trace back its orbit to the far reaches of the outer part of the asteroid belt. The radar data helped meteorite hunters to recover a total of 77 specimens, with the first ones found only two days after the fall. The meteorite was named Sutter's Mill, after the location where it fell. (Interestingly, Sutter's Mill was the place where gold was discovered in 1848, sparking the Californian gold rush.)

To study the meteorite, an international research consortium was assembled by local meteor astronomer Peter Jenniskens, PhD. The team included scientists from The Field Museum's Robert A. Pritzker Center of Meteoritics and Polar Studies and the University of Chicago. The Chicago group consisted of Robert A. Pritzker Assistant Curator Philipp R. Heck, PhD, and University of Chicago Professor and Field Museum research associate Andrew M. Davis, PhD, and senior scientist Stephen B. Simon, PhD.

The Sutter's Mill meteorite was scrutinized by almost the entire arsenal of observational and analytical state-of-the-art tools available to scientists today. The impressive synthesis of the collective results is published in this week's edition of the journal Science. Dr. Heck and his colleagues studied a piece of the meteorite that was donated to The Field Museum by meteorite collector and philanthropist Terry Boudreaux. Dr. Heck prepared a polished section of the meteorite that he and his colleagues first studied with a scanning electron microscope to prepare a petrographic description and produce high-quality X-ray maps to determine its chemical composition.

Together with analysis performed by 43 other institutions, it was discovered that the Sutter's Mill meteorite is a so-called carbonaceous chondrite which is much more diverse in its composition than other meteorites of this type. The unique rock came from a dark, carbon-rich asteroid that experienced an unexpectedly large variety of geological processes on its surface. The reflectance spectrum of the Sutter's Mill meteorite suggests it is similar tothe asteroid that will be visited by the Japanese space mission Hayabusa-2 in 2018. Thus, this meteorite seems to be the ideal sample to prepare cosmochemists for the arrival of Hayabusa-2.

Dr Heck, the curator-in-charge for meteorites at The Field Museum says, Iam fortunate to study this interesting, rare and unique meteorite, and will also preserve pristine pieces of it at The Field Museum for future generations of scientists who will be armed with analytical tools of which we can only dream of today.