Scientists had expected to find buried evidence of several large, potentially “planet killing” asteroid impacts on the moon, as predicted by several computer models. But data collected by NASA’s now-defunct, gravity-mapping GRAIL satellites show only one, previously known, behemoth crater on the moon, the 1,550-mile wide Aitken basin on the lunar south pole, according to a paper published this week Science Advances, a new journal.
Crater size provides an important measure of what was happening in the early days of the solar system. During the so-called Late Heavy Bombardment, which scientists believe occurred about 4 billion years ago -- just a few hundred million years after the solar system’s formation -- Earth and the newly formed inner planets were targets in a celestial shooting gallery.
Computer models suggest the blitz was triggered by Jupiter and the giant planets shifting orbits, causing a barrage of rocky bodies and comets to be gravitationally slingshot inward. But impact basins uncovered by GRAIL don’t fit neatly into those models, astronomer and geophysicist Gregory Neumann, with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, told Discovery News.
“We have more of the medium-size impactors that formed the ‘face’ of the moon, Imbrium (a vast lava-filled crater), and so forth, and we don’t find evidence for larger impactors other than Aitken,” Neumann said. “The implications are enormous.”
“We have been writing this paper since 1996, trying to get an inventory of lunar impact basins from gravity. We haven’t had the gravity field that we’ve needed to do the job until now,” added GRAIL lead scientist Maria Zuber, with the Massachusetts Institute of Technology.
Overall, the number of impact basins uncovered by GRAIL was in the ballpark of what most researchers expected, Zuber told Discovery News.
Read more at Discovery News
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