The Moons Largest Impact Basin
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The Moon's Largest Impact Basin

November 30, 2012
How can we find out just how old the SPA impact basin is? The best way would be to sample materials from the interior of the basin and use radiometric age-dating techniques to determine when they were last molten, as heat from the impact would have melted a large volume of material, resetting radiometric clocks. But the basin is so old that its surface has been cratered many times over, meaning that some of the rocks would have had their radiometric ages reset by these subsequent impacts. So it may be difficult to find rocks with ages that truly reflect the SPA event without careful consideration of the local geology. The region of interest, highlighted in the NAC detail above and outlined in the WAC mosaic below, was selected because it is in a deep portion of the basin, where a large volume of melt would be expected. Some of this melt would remain as a significant component of the soil, and an analysis of a carefully selected suite of samples from this region would reveal the age of the oldest lunar impact basin. One final note - imagine the view of the moon from the Earth when the SPA impact occurred. What would it have looked like? How much ejecta would have landed on the Earth? How long would it take for ejecta to reach the Earth? Surely this impact profoundly affected the young Earth. Where would the best sample site be? Browse the full-resolution NAC image and WAC mosaic and decide for yourself! WAC monochrome mosaic of the interior of SPA, zoomed in to show the 40x40 km region of interest (white box) and surroundings [NASA/GSFC/Arizona State University].

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