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490 Veritas ( ) is a large asteroid, which may have been involved in one of the more massive asteroid-asteroid collisions of the past 100 million years. It was discovered by German astronomer Max Wolf on September 3, 1902 at Heidelberg. At 115 and 125 km in diameter, Veritas and 92 Undina are the largest of the 300-strong Veritas family of asteroids. Apparently there is a whole Veritas family of asteroids including 490 Veritas, 844 Leontina, 1086 Nata, 2428 Kamenyar, 2934 Aristophanes, 5592 Oshima, and 7231 Porco and some other unnamed asteroids. David Nesvorný of the Southwest Research Institute in Boulder traced the orbits of these bodies back in time, and calculated that they formed in a collision of a body at least 150 km in diameter with a smaller asteroid some 8 million years ago. Veritas and Undina would have been the largest fragments of that collision. Substantiating Nesvorný's estimate, Kenneth Farley ''et al.'' found evidence in sea-floor sediments of a fourfold increase in the amount of cosmic dust reaching Earth's surface, which began 8.2 million years ago and tapered off over the next million and a half years. This is one of the largest increases in dust deposits of the past 100 million years.〔 The suspected Veritas collision would have been too far from Jupiter for the fragments to have been slung into a collision course with Earth. However, solar radiation would have caused the resulting dust to drift inward to Earth orbit over a time span consistent with the record of dust in the ocean sediment. Today continuing collisions among Veritas-family asteroids are estimated to send five thousand tons of cosmic dust to Earth each year, 15% of the total. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「490 Veritas」の詳細全文を読む スポンサード リンク
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