One more update to the Late Heavy Bombardment story, then I’ll shut up about it. I started that story with a discussion of Dhofar 961, a lunar meteorite that many think is the only found meteorite to have been chipped off of the South Pole Aitken Basin, the biggest and oldest basin on the moon, and the one that, once dated, should mark the beginning of the Late Heavy Bombardment. (Statistically, this is long overdue: There are more than 60 lunar meteorites, and South Pole Aitken covers almost 15% of the lunar surface. If meteorites fall from the moon to Earth randomly, then geologists should have around 10 from South Pole Aitken.)

Now, Brad Joliff, of Washington University in St. Louis, Missouri, says he’s even more sure it hails from the hole at the bottom of the moon. “We’ve tightened the argument by using more of the geochemistry that’s available.”

He used gamma-ray spectrometry data from Lunar Prospector for six main elements that had been tallied for each of hundreds of 5-degree squares on the moon. Comparing Dhofar 961’s composition to each of the lunar squares, Joliff found that 9 out of the top 10 possible origins all lie within South Pole Aitken Basin. Next step: doing the painstaking radioisotopic dating work on miniature cores from the Dhofar sample.