The Moon's South Pole-Aitken basin is the largest crater in the solar system. It was formed when an asteroid crashed into the lunar surface a long time ago.

In a new study, scientists suggested that the remains of that asteroid are still buried underneath the ancient crater.

Mystery Of The South Pole-Aitken Basin

While analyzing the data collected during NASA's Gravity Recovery and Interior Laboratory, or GRAIL, mission and the Lunar Reconnaissance Orbiter, a team of researchers from Baylor University noticed an anomaly between the surface topography and the gravitational tug of the moon.

"When we combined that with lunar topography data from the Lunar Reconnaissance Orbiter, we discovered the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin," explained Peter B. James, an assistant professor of planetary geophysics and the lead author of the study. "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."

The South Pole-Aitken basin, as its name suggests, is located near the lunar south pole. It is oval-shaped and measures about 2,000 kilometers. Scientists believe that the crater was formed 4 billion years ago.

Remains Of A Massive Asteroid

Whatever the mass is, it is weighing the basin floor downward by more than half a mile, the researchers shared. They tried computer simulations of large asteroid impacts and found that under the right conditions, pieces of an iron-nickel core might have been dispersed into the upper mantle.

"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 Moon's core," James stated.

Another possible explanation for the anomaly is a concentration of oxides in the area. Oxides might have formed when the Moon's ancient magma ocean cooled and solidified.

The researchers noted that larger asteroid impacts might have had occurred throughout the solar system, but none of those have left traces like the one that crashed on the lunar surface to form the South Pole-Aitken basin. James called the crater "one of the best natural laboratories for studying catastrophic events" that was influential to the evolution of rocky planets and moons.

The researchers published the study in the Geophysical Research Letters on April 5.