According to new research from Baylor University published in the journal Geophysical Research Letters, a mysterious large mass of material has been found beneath the most massive crater in the solar system - the South Pole-Aitken basin of the Moon - and may contain metal from the asteroid that crashed into the Moon and formed the crater.
The assistant professor of planetary geophysics in Baylor's College of Arts and Science, and also the leader of the research, Peter B.James, Ph.D., noted that imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground. That's roughly how much-unexpected mass they detected.
Oval in shape, the crater is as broad as 2,000 kilometers, roughly the distance between Waco, Texas, and Washington, D.C., and several miles deep. It is not possible to see it from Earth despite its size and because it is on the far side of the Moon.
For the researchers to measure subtle changes in the strength of gravity around the Moon, they analyzed data from spacecraft used for the National Aeronautics and Space Administration (NASA) Gravity Recovery and Interior Laboratory (GRAIL) mission.
According to James, when they combined that with lunar topography data from the Lunar Reconnaissance Orbiter, they found the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin. He explained further that one of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the mantle of the Moon.
James noted that whatever it is and wherever it came from, the dense mass is weighing the basin floor downward by more than half a mile. Computer simulations of significant asteroid impacts suggest that, under the right conditions, an iron-nickel core of an asteroid may be dispersed into the upper mantle (the layer between the Moon's crust and core) during an impact.
James explained that they did the math and revealed that a sufficient dispersed core of the asteroid that made the impact could remain suspended in the Moon's mantle until the present day, rather than sinking to the Moon's core. Another possibility could be the enormous mass that might be a concentration of dense oxides connected with the last stage of lunar magma ocean solidification.
The South Pole-Aitken basin, believed to have been created about 4 billion years ago, is the most massive preserved crater in the solar system, according to James. While more substantial impacts may have occurred throughout the solar system, including on Earth, most traces of those have been lost. He concluded that the basin is one of the best natural laboratories for studying catastrophic impact events, an ancient process that shaped all of the rocky planets and moons we see in the present day.