On the far side of the moon, buried nearly two hundred miles under the South Pole-Aitken basin (the largest preserved crater in our solar system), is a mysterious mass. Peter B. James and his team of scientists from Baylor University believe it could be the metal core of an asteroid which head-butted the moon and left that 1,242-mile-wide crater behind. It's thought to be the largest and oldest intact crater on any planetary body within the solar system. "That's roughly how much unexpected mass we detected", James said in a statement.
We can't see it from here on Earth, but detailed readings made using lunar orbiters indicate there is something huge enough under that crater to be causing a significant gravitational anomaly.
Scientists aren't sure what exactly the newly discovered mass is. The South Pole-Aitken (SPA) basin is shown by the shades of blue.
As the oval-shaped crater can not be seen from Earth because of its location on the far side of the Moon, researchers analysed data from spacecrafts used for NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission.
For the study, researchers analyzed data from spacecraft used for the National Aeronautics and Space Administration (NASA) Gravity Recovery and Interior Laboratory (GRAIL) mission to measure small changes in the strength of gravity around the Moon. Deep below the moon's South Pole-Aitken basin (the largest preserved impact crater anywhere in the solar system), researchers have detected a gargantuan "anomaly" of heavy metal lodged in the mantle that is apparently altering the moon's gravitational field. The dashed circle shows the location of the mass anomaly under the basin.
Scientists at Baylor University in Waco, Texas, have discovered an unusual metal mass buried at the south pole of the moon, one that likely originated some four billion years ago from a head-on collision with an asteroid.
"The dense mass - whatever it is, wherever it came from - is weighing the basin floor downward by more than half a mile".
An image of the lunar surface showing its various basins.
Even though larger impacts could have occurred throughout the solar system, including on our planet, most traces of larger impacts are no longer available. Computer simulations of large 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.
The team notes that a concentration of dense oxides associated with the final stages of a magma ocean solidifying inside the moon would also produce the same readings.
So, some 4 billion years ago, a mostly metallic asteroid hit the moon and remains embedded in the mantle to this day. These impact basins are said to control the moon's geology.