that Vesta's orbital location was not propitious for providing a significant flux of meteorites in Earth-crossing orbits A finite element code has been developed to model the thermal history of Asteroid 4 Vesta. This is the first attempt to (e.g., Wetherill 1987). However, the discovery of a cluster model the thermal history of a differentiated asteroid through of small V-type asteroids (objects with albedos and absorpcore and crust formation and subsequent cooling until geochemtion features similar to Vesta) having orbits extending from ical closure is attained. The results of the simulation are consisthe region around Vesta to the edge of the 3 : 1 mean tent with chronological measurements and other constraints motion commensurability with Jupiter at 2.5 AU (Binzel provided by cumulate and noncumulate eucrites believed to and Xu 1993) has resolved this problem. The small asterhave been derived from Vesta. The work solves two major oids have been interpreted as ejecta from a large impact problems with the hypothesis of heating by decay of 26 Al, an onto Vesta (Binzel and Xu 1993), and ejecta reaching the extinct radionuclide, postulated to be a plausible heat source 3 : 1 resonance can be readily transferred into Earth-crossin the early Solar System. First, the model demonstrates that it is possible to keep the mantle of Vesta hot for Θ100 Ma, ing orbits (e.g., Wisdom 1985, Farinella et al. 1993). The thereby explaining the observed difference in ages between absence of another large V-class asteroid and the demoncumulate and noncumulate eucrites. Second, the simulation stration of a delivery mechanism to transport meteorites offers a possible explanation of why detectable excesses of 26 Mg from Vesta to Earth add a new perspective to studies of (the decay product of 26 Al) are not observed in noncumulate HED meteorites. Vesta is now generally recognized as a eucrites. The simulation draws a model chronology of Vesta third specific extraterrestrial body (in addition to the Moon and predicts times (relative to CAI formation) for accretion at and Mars) for which actual rock samples are available for 2.85 Myr, core formation at 4.58 Myr, crust formation at 6.58 laboratory analysis. Petrogenetic, geochemical, and chro-Myr, and geochemical closure at Θ100 Myr for a H-chondrite nologic constraints on the formation of HED meteorites asteroidal bulk composition. Decay of 60 Fe is found to cause no perceptible difference in the thermal history of Vesta, even allow the thermal history of Vesta to be modeled with when sequestered into a central core. Although chondritic xenomore assurance than for other differentiated asteroids.
liths have not been described in HED igneous lithologies, the
The importance of studying the thermal evolution of thermal model suggests the possibility that a veneer of unmelted Vesta is twofold: to gain insights into nebular processes and near-surface material should remain.