What if there are parts of another planet on Earth?

Are two scientific mysteries about to be solved? On Wednesday, scientists proposed a new theory that could tell us more about the Moon and the interior of our planet.

The first mystery is the origin of the Moon, for which the most generally accepted theory is that it emerged after a forming planet collided with the future Earth 4.5 billion years ago. The impact with Theia, a protoplanet the size of Mars, would have thrown enough material into space to form the Moon.

All that remains is to find Theia’s remains. According to a study published in the journal Nature by a group of scientists from mostly American institutions, they look below the ground rather than into the air.

Two “drops” under Africa and in the Pacific Ocean

At a depth of 2,900 km below the earth’s surface, two large “blobs” have intrigued scientists since their discovery using seismic waves in the 1980s. continent lying under Africa and the Pacific Ocean.

They are warmer and denser than their surroundings. And the researchers’ computer modeling suggests that these masses are “buried relics” of Theia, which entered Earth during the impact.

The impact was “the most violent event the Earth has faced” in its history, Qian Yuan, a geodynamics researcher at the California Institute of Technology (CalTech) and first author of the study, told AFP. According to him, it is “very, very strange” that there are no visible traces of him. And what prompted him to think: “Where is the drummer? My answer: underground. »

Space and geology

The research led to collaboration between experts from two very different specialties: space and geology. Theia impacted the then-inflicted Earth at more than 36,000 km/h, a speed sufficient for part of the impactor to penetrate “very deep into the Earth’s lower mantle.”

These pieces of essentially molten rock, several tens of kilometers wide, cooled and, solidifying, sank to the limits of the mantle and the earth’s core. This was helped by a higher proportion of iron oxide than in the terrestrial environment, which made them heavier.

They have accumulated into two separate masses, each larger than the Moon, according to Qian Yuan, who also insists that these findings remain the product of necessarily imperfect models and simulations.

“Significant find”

An expert in earth sciences and planetary science from Scotland’s University of Stirling told AFP that the theory put forward by Qian Yuan was “consistent with several existing clues.” “This is an important finding,” said Christian Schröder, who was not involved in the study.

Even if, he said, it does not solve the question of the origin of the Moon, this theory provides “a credible explanation for the anomalies observed at the boundary of the mantle and core.” As for Theia’s remains, they could well “be responsible for important ongoing processes on Earth.”

These masses are known to carry plumes from the mantle, rising magma, to the surface of the earth’s crust. A phenomenon associated with volcanic eruptions, as well as the evolution of supercontinents.

According to Qian Yuan, Theia’s influence “played a role in the evolution of the Earth over 4.5 billion years.” And this is what, he says, will make it “unique (…) different from other rocky planets.”