Scientists have proposed that the wreckage of a long-lost alien world is buried about 1,800 miles under our feet, reports a new study. This mind-boggling hypothesis suggests that strange anomalies in Earth’s interior may be relics of a world that smashed into our planet some 4.5 billion years ago, and that similar ancient remnants may lurk inside other celestial bodies.The infant solar system was much wilder and more tumultuous than it is today, with lots of crashes between small embryonic worlds called protoplanets. Scientists have long suspected that an ancient protoplanet known as Theia, which could have been as large as Mars, hurtled into Earth in this period. This catastrophic collision ejected debris from Theia and Earth into space, where it eventually coalesced into the Moon, so the theory goes.
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Now, scientists led by Qian Yuan, a postdoctoral scholar in geophysics at the California Institute of Technology, present new evidence that remnants of Theia may have also become lodged deep in the Earth’s mantle, where they have survived to the present day. This hypothesis could explain the curious presence of two massive “blobs” inside Earth known as large low-velocity provinces (LLVPs), which appear denser than the surrounding mantle in seismic observations of our planet’s interior, since seismic waves travel through them at a significantly lower velocity than in surrounding material. Yuan and his colleagues “show that LLVPs may represent buried relics of Theia mantle material (TMM) that was preserved in proto-Earth’s mantle after the Moon-forming giant impact” and note that “similar mantle heterogeneities caused by impacts may also exist in the interiors of other planetary bodies,” according to a study published on Wednesday in Nature.“The initial condition of Earth may play a crucial role in Earth's evolution and many uniquenesses,” Yuan told Motherboard in an email. “And that initial condition is widely believed to be set by the Moon-forming impact.”Yuan first started pondering whether the LLVPs might be remnants of Theia years ago while he was pursuing his PhD at Arizona State University. He developed the concept with his colleagues using geodynamical models, and formally presented it at the 52nd Lunar and Planetary Science Conference in 2021.
Now, Yuan and his team have built on those initial findings by running much more advanced simulations of the giant impact that likely formed the Moon, as well as the long-term fallout of this clash inside the infant Earth. The researchers investigated whether the LLVPs, which are each several hundred miles across, could feasibly be remnants of Theia that became entrapped in our planet as it reeled from the collision 4.5 billion years ago.“The significant improvements we have this time are from the Moon-forming impact simulations,” explained Yuan, who credited his co-authors Hongping Deng and Jacob Kegerreis for the advanced models. “Both of their impact simulations show this collision did not melt the whole Earth's mantle, and the lower half of Earth's mantle is mostly solid and it captures an amount of Theia's mantle (~2% of Earth's whole mass ) that is consistent with the Earth's present blobs,” he added. In other words, the team’s new and improved models support the idea that the LLVPs may be the remains of Theia, which helped to create the Moon when it careened into Earth. In addition, Yuan and his colleagues pointed to evidence that the blobs contain primordial elements that predate the Moon-forming impact event. This hints that the LLVPs must be extremely ancient, a timeline that does not fit as well with explanations that suggest the blobs are masses of subducted oceanic crust, or remnants of Earth’s differentiation phase.
It’s utterly wild to imagine that we are all going about our daily lives while continent-sized splinters of a shattered world lurk beneath our feet, which may even be leaking extraterrestrial materials to surface basalt through plumes in the interior of Earth. But while this hypothesis is highly compelling, it will take much more research and experimentation to bear it out.To that end, Yuan and his colleagues hope that parts of Theia may be preserved on the surface of the Moon, which is far more accessible than the deep layer of Earth where the LLVPs exist. “I look forward to seeing future missions on the Moon to bring back its mantle rocks, which are very likely to come from the impactor Theia according to the majority of Moon-forming impact simulations.” Yuan said. “If the lunar mantle rock and LLVP-related basalts share the same chemical signatures, they should both originate from Theia.”Moreover, the team noted that other planets may also contain the fossils of ancient worlds inside their bellies, given that impacts appear to be very common in many early star systems. NASA’s InSight mission to Mars, which ended last year, has revealed unprecedented details about the red planet’s interior, and future missions could potentially detect the relics of extraterrestrial worlds within other extraterrestrial worlds, like otherworldly nesting dolls. “I've been talking to people who work on InSight data about the possibility, but since it only has one seismometer, I imagine it will be very very challenging to observe the 3D structures of the blobs if Mars has them,” Yuan concluded. “Most of the InSight work is still working on 1D structures of its interior, but since Mars has been suggested to have had a giant impact to form the crustal dichotomy, it may have related heterogeneities, which needs future more seismometers to test the hypothesis.”