Scientists combined the two types of data and saw a mismatch between the surface topography and the gravitational tug of the moon, according to a paper published April 5 in the journal Geophysical Research Letters.
"Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground", said the study's lead author Dr Peter James.
The other mission was the Gravity Recovery and Interior Laboratory (GRAIL), which involved two spacecraft - GRAIL A and GRAIL B - working in tandem to detect variations in the strength of the moon's gravitational field.
The crater is on the far side of the moon and can not be seen from Earth. The mass is located under a crater in the Moon's South Pole-Aitken basin, and researchers believe it could be metallic remnants from the asteroid that caused the crater in the first place.
While I personally would love to believe that this is aliens, Dr James suggests a more reasonable explanation: "One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the Moon's mantle".
This false-color image shows the South Pole-Aitken (SPA) basin region in a topographical map.
The dashed circle shows the location of the mass anomaly under the basin in blue.
The gravitational force of "whatever it is, wherever it came from", James said, is so great that it drags down the floor of the basin by more than 800m.
Another possible explanation for the anomaly, the researchers wrote, is that the area is rich in oxides, which likely would have formed as the moon's ancient magma ocean cooled and solidified.
An image of the lunar surface showing its various basins.
The team ran complicated computer simulations of large asteroid impacts which suggested that - under the right conditions - an asteroid which had an iron-nickel core could have dispersed into the moon's upper mantle during an impact. [NASA/GSFC/Arizona State University].The lunar magma ocean solidification is a hypothesis that explains the early evolution of terrestrial planets, according to Science.gov The hypothesis that explains how the terrestrial planets reach their long-term solid-state planet dynamics is however poorly understood, according to the portal. This is an impact crater that stretches about 1,600 miles in diameter.
For these reasons, geologists are eager to explore the basin to glean clues about the moon's formation and composition.
Finding out how the South Pole-Aitken basin formed is important to understanding the history of the moon and its evolution. The crater itself is oval-shaped, as wide as 2,000 kilometers - roughly the distance between Waco, Texas, and Washington, D.C. - and several miles deep. The researchers do not know what the mass is, but it appears to extend down beneath the moon's surface by over 180 miles.
Whatever formed the basin almost 4 billion years ago remains a mystery, but the blow was so strong that it likely punched all the way through the moon's crust and tossed part of the lunar mantle - a deeper geologic layer - onto the surface.