A new paper about the unique, ungrouped achondrite meteorite Northwest Africa (NWA) 7325 is now available online.
Several group members, including Jamie Gilmour, Katherine Joy, Sarah Crowther and Patrica Clay, have contributed to this paper, along with colleagues from the Institut für Planetologie in Münster, Germany, Planetary and Space Sciences at The Open University, UK and Institut für Geologie und Mineralogie, Universität zu Köln in Germany.
NWA 7325 had originally though to be the first meteorite originating from the planet Mercury. This paper presents a comprehensive study of the meteorite, using a wide range of experimental techniques, to test if Mercury is the most likely planetary body from which this sample could have been sourced.
Although the sample has some chemical similarities to the mercurian surface as mapped by NASA’s MESSENGER spacecraft, it has a very old crystallisation age, which implies that it is too old to have originated from the surface of Mercury. None the less, it is a unique and interesting piece of an ancient, unknown planetary body, which has never been sampled before! Oxygen data show similarities to the ureilite group of meteorites, but the mineralogy shows similarities to other groups of achondritic meteorites known as the acapulcoites and lodranites. Minerals in the sample show evidence of a 2nd melting event, but argon isotope data record ancient ages (~4.5 billion years) that have not been reset by more recent metamorphic events. Raman spectroscopy, petrological and cosmochemical data indicate that the meteorite originated from a highly reduced, iron poor parent body, or from a differentiated body that underwent metal-silicate fractionation in highly reducing conditions.
One of the main focuses of this paper is infrared spectroscopy, a non-destructive technique that can quickly investigate mineral phases. MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) onboard the ESA/JAXA BepiColombo mission (due to be launched in 2016) will investigate the mid infrared spectra of Mercury, and the initial analyses on NWA 7325 was undertaken in the hope it would provide an analogue for Mercury. While other data show that this meteorite did not originate from Mercury, the infra red spectra show a good match to data from NASA’s MESSENGER mission, and enable our colleageue in Germany to improve and extend their database of infrared data prior to the upcoming mission.
The full citation for this paper is: I. Weber, A. Morlok, A. Bischoff, H. Hiesinger, D. Ward, K. H. Joy, S. A. Crowther, N. D. Jastrzebski, J. D. Gilmour, P. L. Clay, R. A. Wogelius, R. C. Greenwood, I. A. Franchi and C. Münker. Cosmochemical and spectroscopic properties of Northwest Africa 7325—A consortium study. Meteoritics and Planetary Science. DOI: 10.1111/maps.12586.
Note: Unfortunately this paper in final published form is currently only available online to subscribers of Meteoritics and Planetary Science. However, an authors version is available here to preview here.