"Rock of the Month # 260, posted for February 2023" ---

The Park Forest meteorite fell just before midnight, local time, on 26 March 2003. Following a bright fireball seen in several states, dozens of stones fell to the ground, of total known weight circa 18 kg. Such a scattershot arrival, in contrast to the arrival of a meteoroid that underwent little or no fragmentation during its passage through the upper atmosphere, is referred to as a meteorite shower. Stony meteorites, being less mechanically robust than the less-common iron meteorites, are more likely to break apart in this way, with a thin fusion crust forming on each surface so exposed, as much as tens of kilometres above the surface of the Earth. The event and the meteorite are described in detail by Simon et al.. (2003, 2004).

The Fall

The fall phenomena associated with the Park Forest meteorite fall were studied in detail by Brown et al. (2004). All available lines of evidence were considered. The earliest video recording was made when the incoming meteoroid was near an altitude of 82 km. The fireball brightness attained a peak absolute visual magnitude of -22, which would have been almost unbearably bright. It was determined that the most probable preatmospheric mass of the meteoroid was 11±3 tonnes, with a diameter of 1.8 m. Based on the contents of short-lived radionuclides in the freshly-fallen meteorite, a somewhat smaller mass was calculated at 0.9 to 7 tonnes (Simon et al., 2003, 2004). This was not an especially large body, but the circa 99% mass loss to atmospheric ablation is impressive. It is easy to imagine how, absent our thick atmosphere, the Earth's surface would be pockmarked like the Moon!

In the case of the 2010 fall of the Kosice H5 chondrite, the calculated aphelion of 4.5±0.5 A.U. is the largest (furthest from the Sun) of 16 meteorites for which orbits had been calculated at that time (Borovicka et al., 2013). The next largest (most distant) aphelion was that of Park Forest at 4.26±0.38 A.U.

The Meteorite

The meteorite was soon described in Meteoritical Bulletin (Russell et al., 2003) and the initial Total Known Weight recovered was quoted at 18 kg. Simon et al. (2004) noted that some material was sold into the market before being counted, and the likely total mass recovered was probably closer to 30 kg. The meteorite is represented in numerous collections, and illustrates books and articles such as Carion (2009) and Sears (2014). A strewnfield map appears in Smith et al., 2009, 2018). When a new fireball event is documented and analysed, and the meteorite recovered, Park Forest is one of the well-constrained cases that are often referenced (e.g., Popova et al., 2011; Jenniskens et al., 2018, 2019).

Samples were found in some 40 sites, some 40 km south of Chicago, over a strewnfield 8 km long, with some 18 kg of material recovered in short order, in pieces as large as 2.7 kg. The meteorite is a breccia with light and dark lithologies (Sears, 2014). In general, light clasts prevail over dark matrix, and metal and sulphide are visible to the naked eye in both lithologies.The chemistry of olivine and orthopyroxene grains is consistent with an L5 chondrite (Simon et al., 2003, 2004). The meteorite is highly shocked, with glassy veins, mosaicism and planar deformation features in olivine, and other factors. In textural terms it is an L5 (S5), well-equilibrated chondrite, with easily recognizable chondrules and maskelynite (shocked plagioclase feldspar glass) mostly no larger than 50 microns (Simon et al., 2004).

References

Arnold,S and Beauford,R (2014) Introductory meteorite fieldwork - part 3: chasing witnessed falls and fireballs. Meteorite 20 no.3, 14-18.

Borovicka,J, Toth,J, Igaz,A, Spurny,P, Kalenda,P, Haloda,J, Svoren,J, Kornos,L, Silber,E, Brown,P and Husarik,M (2013) The Kosice meteorite fall: atmospheric trajectory, fragmentation, and orbit. Meteoritics & Planetary Science 48, 1757-1779.

Brown,P, Marchenko,V, Moser,DL, Weryk,R and Cooke,W (2013) Meteorites from meteor showers: a case study of the Taurids. Meteoritics & Planetary Science 48, 270-288.

Brown,P, Pack,D, Edwards,WN, ReVelle,DO, Yoo,BB, Spalding,RE and Tagliaferri,E (2004) The orbit, atmospheric dynamics, and initial mass of the Park Forest meteorite. Meteoritics & Planetary Science 39, 1781-1796.

Carion,A (2009) Meteorites. Alain Carion, Paris, 3rd edition, translated from the French by Anne Black, 72pp.

Jenniskens,P plus 17 (2018) Detection of meteoroid impacts by the Geostationary Lightning Mapper on the GOES-16 satellite. Meteoritics & Planetary Science 53, 2445-2469.

Jenniskens,P plus 32 (the Creston Meteorite Consortium) (2019) The Creston, California, meteorite fall and the origin of L chondrites. Meteoritics & Planetary Science 54, 699-720.

Popova,O, Borovicka,J, Hartmann,WK, Spurny,P, Gnos,E, Nemtchinov,I and Trigo-Rodriguez,JM (2011) Very low strengths of interplanetary meteoroids and small asteroids. Meteoritics & Planetary Science 46, 1525-1550.

Russell,SS, Zipfel,J, Folco,L, Jones,R, Grady,MM, McCoy,T and Grossman,JN (2003) The Meteoritical Bulletin, No.87, 2003 July. Meteoritics & Planetary Science 38, A189-248.

Sears,D (2014) Meteorites with light and dark structure. Meteorite 20 no.3, 34-35.

Simon,SB, Grossman,L, Clayton,RN, Mayeda,TK, Schwade,JR, Sipiera,PP, Wacker,JF and Wadhwa,M (2004) The fall, recovery, and classification of the Park Forest meteorite. Meteoritics & Planetary Science 39, 625-634.

Simon,SB, Wacker,JF, Clayton,RN, Mayeda,TK, Schwade,JR, Sipiera,PP, Grossman,L and Wadhwa,M (2003) The fall, recovery, and classification of the Park Forest meteorite. Meteoritics & Planetary Science 38, A139.

Smith,C, Russell,S and Almeida,N (2018) Meteorites, the Story of Our Solar System. Firefly Books / Natural History Museum, London, 2nd edition, 128pp.

Smith,C, Russell,S and Benedix,G (2009) Meteorites. Firefly Books / Natural History Museum, London, 112pp.