A previously unknown deposit of an unidentified physical substance larger than the size of Hawaii has been discovered beneath the surface of the moon. Scientists at Baylor University published a study detailing their findings of this "anomaly" beneath the moon's largest crater, at its South Pole. They believe the mass may contain metal carried over from an earlier asteroid crash.

According to the study — "Deep Structure of the Lunar South Pole-Aitken Basin" — which was published in the journal Geophysical Research Letters in April, the large mass of material was discovered beneath the South Pole-Aitken crater, an oval-shaped crater that is 2,000 kilometers (about 1,243 miles) wide and roughly 4 billion years old. According to Baylor University, the unidentified mass was discovered "hundreds of miles" beneath the basin and is "weighing the basin floor downward by more than half a mile."

"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 we detected," said lead author Peter B. James, Ph.D., assistant professor of planetary geophysics in Baylor's College of Arts & Sciences.

Get Breaking News Delivered to Your Inbox

Baylor scientists discovered the mass by analyzing data taken from spacecraft used during NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. The GRAIL mission was a lunar gravity mapping exploration that used two spaceships to study the moon's interior and thermal history.

Scientists aren't sure what exactly the newly discovered mass is. According to the published study, "Plausible sources for this anomaly include metal from the core of a differentiated impactor or oxides from the last stage of magma ocean crystallization," which hypothesizes the moon's surface was once a molten liquid ocean of magma.

Baylor scientists believe the mass may also be suspended iron-nickel core from an asteroid that previously impacted the moon's surface.

"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," James said.