Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..323b&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 323
Other
Basaltic Achondrites, Diogenites, Eucrites, Howardites, Impacts, Parent Bodies, Vesta
Scientific paper
For more than two decades, asteroid 4 Vesta has been debated as the parent body for the howardite, eucrite, and diogenite (HED) classes of basaltic achondrite meteorites. Among large main-belt asteroids, Vesta's basaltic achondrite spectral properties are unique. Given this unique spectroscopic match and reasoning that the HED parent body must be large and intact, [1] has argued that Vesta is the most likely source. However, as pointed out by [2], it is dynamically difficult for sizable samples to be ejected from Vesta (diameter 520 km, escape velocity 365 m/s). Further, Vesta is located far from the 3:1 and the nu(sub)6 resonances, making transfer of its ejecta to the inner solar system via one of these "escape hatches" very inefficient. Recent observational results [3] now appear to establish Vesta as a dynamically viable source for the HED meteorites. Telescopic measurements have revealed twenty small (diameters <10 km) main-belt asteroids that have distinctive optical reflectance spectral features similar to Vesta and eucrite and diogenite meteorites. Twelve are located in the immediate vicinity of Vesta and were previously predicted to be dynamically associated with Vesta [4,5]. Eight bridge the orbital space between Vesta and the 3:1 resonance. More than 100 other small main-belt asteroids were also spectroscopically surveyed [3], but basaltic achondrite compositions were found only for objects in the same orbital element space (inclination and eccentricity) as Vesta. The spectroscopic match and coincidence of location implies that these newly discovered basaltic achondnte asteroids are most likely multikilometer-sized fragments excavated from Vesta through one or more impacts. The existence of these Vesta-related fragments apparently demonstrates that major impacts are capable of ejecting multikilometer blocks with velocities in excess of 500 m/s. Such ejection block sizes and velocities have been previously suggested in studies of secondary craters on the Moon, Mercury, and Mars [6]. The discovery of Vesta fragments in the vicinity of the 3:1 resonance makes it dynamically viable for Vesta samples to be transported to the inner solar system for delivery to the Earth as meteorites. With this new compositional and dynamical link, researchers may begin to consider that studies of HED meteorites and of the geology of Vesta are one in the same [7]. References: [1] Drake M. J. (1979) In Asteroids (T. Gehrels, ed.), Univ. of Arizona, p. 765. [2] Wetherill G. W. (1987) Philos. Trans. R. Soc. Lond., A323, 323. [3] Binzel R. P. and Xu S. (1993) Science, 260, 186. [4] Zappala V. et al. (1990) Astron. J., 100, 2030. [5] Williams J. G. (1992) Icarus, 96, 251. [6] Vickery A. M. (1987) GRL, 14, 726. [7] Gaffey M. J. (1993) Science, 260, 167.
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