Cat Mountain: A meteoritic sample of an impact-melted asteroid regolith

David A. Kring, Timothy Swindle, Daniel T. Britt, Jennifer A. Grier

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

Cat Mountain is a new ordinary chondrite impact melt breccia that contains several shocked chondrule-bearing clasts of L5 material. These clasts are surrounded by a total impact melt of similar composition material which appears to have cooled over a period of a few thousand years, probably within a melt breccia lens in the bottom of a large (>1 km diameter) crater on an L chondrite asteroid. Noble gas isotopes indicate that the sample was involved in at least two different impact events, approximately 880 and 20 Myr ago, followingGA the 4.55 Ga accretion of primitive chondritic material. The 880 Ma event is responsible for the impact breccia texture of the sample, and the 20 Ma event reduced the sample to a meter-sized object. We also infer that another impact occurred between 880 and 20 Ma (possibly the ∼500 Ma event recorded in many other L chondrites) to jettison the material from the asteroid belt into an orbit that evolved into an Earth-crossing trajectory. The shock-metamorphic processes that occurred at 880 Ma redistributed the opaque phases in the meteorite and altered the crystalline characteristics of silicate phases. This reduced the reflectance of the L5 material and decreased the amplitude of its spectral absorption features. These characteristics are consistent with the spectral characteristics of some C class asteroids and suggest that some dark asteroids that appear to belong to the C class could be covered with shocked ordinary chondrite material. If one assumes that Cat Mountain came from the same asteroid as other L chondrites with the same cosmic ray exposure age, then the juxtaposition of these different materials suggests asteroids are rubble piles which are heterogeneous on a scale less than 100 m. Furthermore, the structural integrity of Cat Mountain and other L chondrites suggests the strengths of asteroid rubble piles are limited by fractures and contrasting material properties and are thus inherently weak in a ram pressure regime produced when they enter a planetary atmosphere. However, in a regime where the asteroid is the target of impact fragmentation rather than the projectile, the added porosity of a rubble pile structure will compensate for the presence of fractures and absorb a large amount of the impact energy. In this case the structural integrity of the asteroid may appear to be the same as a previously unshocked chondritic material.

Original languageEnglish (US)
Pages (from-to)29353-29371
Number of pages19
JournalJournal of Geophysical Research: Space Physics
Volume101
Issue numberE12
StatePublished - 1996

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Asteroids
regolith
cats
asteroids
mountains
asteroid
chondrites
mountain
breccia
chondrite
piles
impact melts
Piles
pile
ordinary chondrite
melt
Structural integrity
integrity
clast
Bearings (structural)

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Atmospheric Science
  • Geochemistry and Petrology
  • Geophysics
  • Oceanography
  • Space and Planetary Science
  • Astronomy and Astrophysics
  • Earth and Planetary Sciences(all)
  • Environmental Science(all)

Cite this

Cat Mountain : A meteoritic sample of an impact-melted asteroid regolith. / Kring, David A.; Swindle, Timothy; Britt, Daniel T.; Grier, Jennifer A.

In: Journal of Geophysical Research: Space Physics, Vol. 101, No. E12, 1996, p. 29353-29371.

Research output: Contribution to journalArticle

Kring, David A. ; Swindle, Timothy ; Britt, Daniel T. ; Grier, Jennifer A. / Cat Mountain : A meteoritic sample of an impact-melted asteroid regolith. In: Journal of Geophysical Research: Space Physics. 1996 ; Vol. 101, No. E12. pp. 29353-29371.
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