THE shattered remnants of a dwarf planet may have bombarded the inner planets in the early solar system, suggests a new analysis of craters on the moon.
Several large impact scars on the moon appear to be around 3.9 billion years old, suggesting that the Earth and other objects of the inner solar system were heavily pounded at that time. Most astronomers believe that the bombardment was caused by shifts in the orbits of the giant planets, which destabilised the asteroid belt, hurling giant rocks our way.
But the distribution of small and large lunar craters does not match the numbers of small and large objects in the asteroid belt today, says a team led by Matija Cuk of Harvard University, who spoke at a meeting of the American Geophysical Union in Toronto, Canada, last week.
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Cuk says one possible alternative is that a dwarf planet or single large asteroid 鈥渉undreds or maybe 1000 kilometres across鈥� did the damage after being ripped apart by gravity when it came too close to Earth or another inner planet. It then littered the inner solar system with impactors.
Bill Bottke of the Southwest Research Institute in Boulder, Colorado, doubts a shattered 1000-kilometre object can explain all the damage in this period. He thinks the standard picture is closer to the truth but admits: 鈥淲e still don鈥檛 understand the full story.鈥�
