PEEKSKILL


H6
standby for peekskill photo
Fell October 9, 1992
41° 17' N., 73° 55' W.

At 7:48 P.M. a greenish fireball brighter than the full moon appeared over Kentucky and traveled in a near-grazing trajectory of only 3.4° for more than 700 km in a north–northeasterly direction for at least 40 seconds, finally landing in Peekskill, New York. A sonic boom was heard as it fragmented into over 70 pieces, one of which impacted the trunk of a red Malibu coupe (see photo below) on 207 Wells St., the home of Michelle Knapp. When police arrived on the scene, they filed a report for criminal mischief by a very strong male. The smell of gas from the punctured gas tank finally prompted the fire department to investigate, at which time they found the meteoritic culprit. The stone was impounded by the police and subsequently fractured to see what was inside. This famous meteorite was eventually returned to the rightful owners.

The flight path of the Peekskill meteoroid was recorded on at least fourteen amateur videos, making this the first video obtained of a recovered meteorite. It was concluded from the videos, that there should be at least two, and possibly four or more, fragments which impacted the ground, but only the one 12.4 kg specimen has been recovered to date. Through analysis of these videos, a pre-atmospheric velocity of 14.72 km/s was calculated. The orbital parameters were worked out showing that it was only 41 days past its perihelion of 0.886 AU, with an aphelion distance of 2.1 AU. Only a few other meteorite falls have corresponding photographic, videotape, or satellite references which has enabled their orbits to be calculated; these are Lost City, Pribram, Innisfree, Morávka, Neuschwanstein, and Tagish Lake. Several other meteorite falls were observed well enough to calculate good orbital estimates, including Glanerbrug, Khmelevka, Dhajala, Paragould, Kunashak, Sikhote Alin, Vilna, Archie, Norton County, Nikolskoe, and Tilden, and today many camera networks are operating successfully around the globe determining meteoroid origins (see Almahata Sitta).

A thermal history of the H chondrite parent body was presented by Harrison and Grimm (2010) based on cooling rate data and closure times. They found that the object accreted over a short time period of 2.2 m.y. In an alternative viewpoint, Monnereau et al. (2012) determined a more rapid accretion time period of 0.1–0.2 m.y. while 26Al was still extant. Moreover, Sokol et al. (2007) concluded that accretion of the ~150 km H-chondrite parent body occurred relatively late after most radioactive 26Al had decayed, at least 2 m.y. after CAI formation; it was probably heated by continuing impacts. It is generally considered that the asteroid eventually formed an insulated "onion-shell" structure with a diameter of 150–260 km. The H-chondrite parent body was composed approximately (by volume) of 84%, 10%, and 6% of type 6, type 4/5, and type 3 material, respectively.

Amelin et al. (2005) employed thermal models to calculate the progressive increase in petrologic types from the core to the surface as follows: from the core outward to a distance of 44.9 km is type 6 material; between 44.9 km and 48.9 km is type 5 material; between 48.9 km and 56.9 km is type 4 material; and from 56.9 km to the surface at 92.5 km is type 3 material. Peak temperatures were determined to be 865–1000°C, 675–865°C, and <675°C for type 6, type 4/5, and type 3 material, respectively. The higher petrologic types were excavated at depth by impact, forming craters measuring tens of km wide and reaching depths of 5.6–11.2 km on their 200 km diameter model. Fission track thermochronometry indicates that type 7 chondrites cooled more slowly at greater depths than did those of lower petrologic types (Trieloff et al., 2003). Consequently, type 7 chondrites experienced a longer period of thermal metamorphism within this interior layer, and now they exhibit extensively recrystallized textures that are transitional to an achondrite classification.

Importantly, a complex cooling history for the higher petrologic type H chondrites (5/6) was suggested from thermometric studies conducted by Ganguly et al. (2012). They reconciled data from calculations of two-pyroxene thermometers with the Ar–Ar, Pb–Pb, and Hf–W closure temperatures of select minerals to determine a cooling history consistent with very rapid cooling between ~800°C and 450°C, followed by a very slow cooling stage, and then another rapid cooling stage. By contrast, those H chondrites with lower petrologic types experienced a steady state of very rapid cooling. It was proposed that this scenario was more consistent with a collisional disruption and re-accretion of the parent body as opposed to a smoothly transitional "onion shell" model.

Through analysis of radionuclides and cosmic ray tracks, a cosmic-ray exposure age of 32 m.y. was obtained, consistent with the earliest of three distinct impact events determined to have occurred at ~7.0, 22, and 33 m.y. ago. Peekskill is considered to have experienced a two-stage irradiation exposure. During the first stage, the sample was located 20–25 cm deep on a meteoroid having a radius of 40–60 cm. During the second stage, which lasted less than 200 k.y., the depth was >7 cm with a radius of 25–40 cm. A study was undertaken by V. Alexeev (2004) to determine the average atmospheric ablation of 83 ordinary chondrites utilizing cosmic ray tracks. He calculated an average ablation of 78.4% (±3) for the entire chondrite study group, while Peekskill had a very high ablation of ~97%.

The Peekskill meteorite along with the famous red Malibu coupe, the latter having been purchased by meteorite collector A. Langheinrich (presently owned by D. Pitt), have been taken on tour through several countries including Germany, France, Japan, and Switzerland, as well as throughout the USA. The specimen of Peekskill shown above is a 0.72 g fragment with fusion crust exhibiting a faint smear of red paint transferred upon impact with Michelle Knapp's car (see photo below). A video of the arrival of the Peekskill meteorite can be seen below.

standby for peekskill car photo
Photo by Walt Radomsky. Courtesy of R. A. Langheinrich Meteorites

Peekskill video—launch in external player