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D.K. Yeomans (JPL/CalTech)
While early meteorite falls had been observed by Chinese and European observers and lunar craters were identified in the early seventeenth century, the important role of impacts in determining the surface features of the moon and Earth would not be widely recognized for more than three centuries. Despite the fact that Earth's volcanic craters were dissimilar in both size and shape from lunar craters, a volcanic origin for the lunar craters was favored. The impact origin for these craters was not seriously discussed until the early twentieth century. Until then, near-Earth asteroids were unknown and it was difficult to explain why the observed lunar craters had circular rims when those created by impacts should have oblong rims to reflect the oblique approach angle of most impactors. Although Opik first pointed out in 1916 that lunar impactors coming in at any angle would create explosive events that could explain the near circularity of their crater rims, his paper was buried in an obscure journal. In the first half of the twentieth century, the consensus view of astronomers was that volcanic activity was responsible for lunar craters while geologists leaned toward an impact origin. Thus, each group dismissed the mechanism that was most familiar to them. At a time when most astronomers stubbornly refused to acknowledge any impact craters on the moon or Earth, the geologist and entrepreneur Daniel Barringer doggedly championed the impact formation of the Meteor crater near Flagstaff Arizona. It was not until 1980 that Alvarez et al suggested and provided evidence for an impact extinction event that corresponded with the boundary between the Cretaceous and Tertiary periods some 65 million years ago. The issue of an engineering solution for the mitigation of an Earth threatening object (i.e., Project Icarus) was first studied in 1967 by an undergraduate engineering class at MIT.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.