On Friday, July 14 at 10:15 A.M., a fireball traveling in a north-northwest direction exploded over the town of Moss, Norway, in the county of Ostfold, located about 50 km south of Oslo on the east side of Oslofjord. The fall was accompanied by a loud explosion and thunderous rumblings, and numerous calls and reports were made by eyewitnesses to the event. A clear signal was picked up at the Norwegian Seismic Array (NORSAR) in Kjeller, Norway.
Meteorite fragments fell over a wide area. In the vicinity of Rygge, located ~6 km southeast of Moss, the sounds were heard by Ragnar Martinsen as he occupied the outhouse behind his holiday cabin. As he exited, he heard a whistling sound followed by the clatter made by a 36.7 g stone hitting a corrugated metal sheet lying just 2 m away. He contacted astronomers from the Astrophysics Institute of the University of Oslo and from the Norwegian Astronomical Society and invited them to his cabin for their educated opinions of his findthey agreed it was a chondritic meteorite.
On Monday, July 17, with intentions of mowing his lawn, Frode Johansen of Moss, Norway discovered a 752 g stone lodged in a 7 cm-deep hole beneath his plum tree; three broken branches attest to its flight path. The family expressed their intensions to donate the meteorite to the Museum of Natural History in Oslo.
On Wednesday, July 19, a large, partially-crusted fragment was found by a local resident northwest of the Johansen find. After reading about the search for the meteorite in the newspaper, he contacted meteorite hunters Michael Mazur and Bjorn Sorheim of Norway. On Sunday, July 23, the resident met with them to show them a fragment of the fall and to share details of the find location. Subsequently, Michael and Bjorn recovered additional fragments from the original 1.5 kg stone that had shattered upon impact with a fence.
On Sunday evening, July 30, Morten Bilet and Michael Farmer were searching near Moss for additional pieces from this fall. They found ~800 g of fragments that had been strewn about following the impact of a single stone on concrete. Some fragments were found in pristine condition up to 20 m away from the point of impact.
On Friday, August 4, a 676 g stone was found which had fallen part way through the roof of a storage warehouse belonging to the Norgesgruppen business in Moss. It had punched a 10-cm hole through the roofing material and was lodged within. Its discovery was made only after rainwater leaked through the hole that it had created. This particular stone is a natural fit to the Johansen stone, and likewise has been donated to the Museum of Natural History in Oslo.
Portions of the preceeding accounts were gleaned from the Aftenposten: News From Norway (http://www.aftenposten.no/english).
Moss is the sixth witnessed fall of a CO3 chondrite, the first since Kainsez fell in Russia in 1937. Significantly more material was recovered from Kainsez than from Moss200 kg compared to 3.76 kg, respectively. While the chromite content of fayalitic olivine can provide petrologic type calibration between 3.0 and 3.1, the low Cr value measured in Moss indicates it is higher than 3.1. A petrographic analysis of Moss was conducted by J. Grossman (US Geological Survey, Reston, VA.), which was based on the technique employed by Chizmadia et al. (2002). This analysis suggests a classification between CO3.5 and CO3.6, and Moss is listed as a CO3.6 in MetBull 91. Petrographic studies by other investigators have provided indications of a lower type (Greenwood et al., 2007). According to the FeMg zoning profiles of olivine in type-I chondrules, a petrologic type closer to 3.4/3.5 was indicated.
Moss contains abundant sub-mm-sized chondrules typical for the CO group, which are embedded in a fine-grained gray matrix. Extensive low-temperature alteration has likely occurred within the solar nebula, perhaps augmented on the parent body as evidenced by wide variation in secondary transformation effects in individual inclusions. Olivine grains within AOAs and spinel within CAIs have been altered to a range of higher FeO levels, while alteration of CAIs has resulted in the production of secondary minerals such as nepheline replacing primary melilite and/or anorthite, and perovskite that has been converted to ilmenite (Bischoff and Schmale, 2007).
Based on 3He and 21Ne values, the CRE ages of the various CO3 chondrite falls show a range of 3.557 m.y., each representing an independent ejection event except for the 21 m.y. ages shared by Kainsaz and Ornans (Bartoschewitz et al., 2010). Cosmic-ray exposure values for Moss are the second shortest known for CO chondrites at 14 m.y. A gas retention age of 3.95 b.y. was found, while a KAr age of 4.43 b.y. was found; the reason for this age difference in Moss has not yet been determined. A study of the trapped noble gases shows that Q-Xe compositions are dominant, with small contributions from air-Xe and possibly from Xe-HL, but that Ar and Kr are present in higher abundances than normal for Q-type gases and likely represents an additional carrier phase. No correlation was found to exist between trapped noble gas abundances and metamorphic grade.
The volume of FeNi-metal and FeS is typical for the proposed classification. As with the CO3.3 Ornans and CO3.1 Kainsaz, Moss contains a low C abundance (0.25 wt%) with a heterogeneous distribution of organic species, all of which have a low molecular weight with a low degree of variation (Pearson et al., 2007). This C abundance is unexpectedly low given its relatively low metamorphic grade, and low when compared to the organic inventory of analogous CO3 members such as CO3.5 Lancé. A micro-Raman study of the organic matter in Moss was undertaken by Yesiltas et al. (2016), and their results indicate the presence of more ordered carbon in some regions of the meteorite consistent with a higher degree of thermal metamorphism than in other CO chondrites. Ornans, Kainsaz, and Moss appear to have experienced unique metamorphic conditions on the parent body.
An O-isotopic analysis of Moss conducted by Franchi and Greenwood (The Open University, UK) provided values which are consistent with the CO carbonaceous chondrite group. A subsequent precise O-isotopic investigation was conducted by Greenwood et al. (2016) of a broad sampling of CO chondrites, including six CO falls (Moss, Feliz, Kainsaz, Lancé, Ornans, and Warrenton) and fourteen primitive Antarctic finds representing at least four distinct meteorites (e.g., DOM 08006 [3.00], DOM 08004, MIL 03377/07099, and ALH 77307 [3.03]). The resulting plots on an oxygen three-isotope diagram resolve two separate clusters of CO chondritesone which includes the primitive Antarctic finds and another which includes the more highly metamorphosed falls. It was noted that the isotopic values of the two more metamorphosed Antarctic meteorites (ALH 82101 [3.3] and MIL 090785 [3.7]) plot within the field of the more metamorphosed CO falls, in support of the existence of two distinct clusters. The investigators suggest that these two CO clusters could reflect the existence of multiple parent bodies, or perhaps more plausible, a greater interaction of the CO falls with an 16O-poor aqueous reservoir. Interestingly, the primitive Antarctic finds plot with the anhydrous silicate component of the CM chondrite Murchison (see the Colony page for further information about a potential COCM genetic relationship).
click on image for a magnified view
Diagram credit: Greenwood et al., 47th LPSC, #2206 (2016)
In their continued study of the CO chondrites listed above, Alexander et al. (2017) found that these meteorites could be divided into two distinct groups based on C abundances and isotopic composition. Even after accounting for isotopic variability due to terrestrial aqueous alteration, two distinct clusters are still apparent composed of the following: 1) 16O-enriched primitive Antarctic finds, and 2) 16O-poor equilibrated CO falls (and the more equilibrated ALH 82101 and Colony finds). The authors suggest the most plausible expanation for these clusters is that the more equilibrated members incorporated higher abundances of a primary 16O-poor water component compared to the primitive Antarctic finds, and they presume that a continuum would otherwise exist among all CO chondritesbounded by an 16O-rich end member like DOM 08006 and an 16O-poor end member like the equilibrated CO falls.
The specimen of Moss shown above is a 1.97 g crusted fragment. The photo below is an excellent petrographic thin section micrograph of Moss, shown courtesy of Peter Marmet.
click on photo for a magnified view
Photo courtesy of Peter Marmet