'When we combined that with lunar topography data from the Lunar Reconnaissance Orbiter, we discovered that the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin, ' James said.
A odd large mass of material has been detected under the Moon's largest crater and may contain metal from an asteroid that crashed into the lunar surface and formed the crater, according to a Baylor University study. "That's roughly how much unexpected mass we detected", said lead author Peter B. James, Ph.D., assistant professor of planetary geophysics in Baylor's College of Arts & Sciences. Despite its size, however, we can't see this crated from Earth because it's on the far (dark) side of the Moon.
However it formed, the fact that the mass anomaly is still so prominent and that it seems to be located about 186 miles (300 km) down also offers scientists an intriguing idea: These facts suggest that the moon's insides can't be all that gooey; if they were, the moon's gravity would pull the massive patch into the lunar center.
At roughly 1,550 miles in diameter, the Lunar South Pole-Aitken basin covers approximately one-fourth of the Moon's surface, according to NASA.
The findings appear in the journal Geophysical Research Letters.
The dashed circle shows the location of the mass anomaly under the basin in blue.
The metal, if that is what is causing the extra mass, is located on the moon's South Pole-Aitken basin, an enormous crater at the bottom of the planet. As a result, they found a dense metallic mass pulling down on the floor of the basin.
The South Pole-Aitken basin, understood to be around 4 billion years old, is the largest preserved crater we have discovered in the solar system - over ten times larger than the largest crater on Earth. From the data, the team theorized it could be the iron-nickel core of an asteroid that lodged itself deep in the upper mantle of the moon, which is that intermediary layer between the crust and core. This large mass may be a remnant of the asteroid that crashed into the Moon and formed the crater - which would also mean that it could be made up nearly entirely out of metal. Meanwhile, the LRO has been mapping the lunar surface for a decade.
"We did the math and showed that a sufficiently 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 lunar core", Dr. James said.
The second theory is that the mass is a concentration of dense oxides leftover from the last stage of what scientists call the lunar magma ocean crystallization. These impact basins are said to control the moon's geology. Essentially, something caused a giant hole on the Moon billions of years ago, and astronomers have just discovered that there's something big - really big - buried underneath the surface.