Thread by @qianyuan_geo

First-ever: We've identified a new astronomical object, 'Buried Planet', using SEISMOLOGY, rather than telescopes. It's a survivor of Theia, the planet that collided with Earth 4.5 billion years ago to form our Moon. See our @Nature cover paper: rdcu.be/dp16K

If the two mantle blobs are remnants of the ancient impactor planet, could other rocky planets also have a 'buried planet'? Planetary seismology, missions like @NASAInSight may help us probe the earliest solar system's history, particularly for Venus which does not have a moon.

Huge thanks to my collaborators, Mingming Li, @Deschscoveries, @ed_garnero from @SESEASU, @yoshi_planetes and Paul Asimow from @Caltech, Hongping Deng, Byeongkwan Ko, Travis Gabriel, Jacob Kegerreis, and Vincent Eke. This work is not possible without your contributions!!🙏

0. Seismologists long discovered two continent-sized basal mantle anomalies, known as 'large low-velocity provinces,' beneath the Pacific and Africa. Traditionally attributed to Earth's differentiation process. Here we propose they originate from the Moon-forming impactor, Theia.

1. We performed state-of-art giant impact simulations, revealing a two-layered mantle structure. The upper layer fully melts, while the lower half remains mostly solid and it surprisingly captures ~10% of the impactor's mantle material, a mass close to current seismic blobs.

2. Since the bulk Moon has higher Fe content than Earth's mantle, the impactor's mantle may be more iron-rich, making it denser than the background mantle. This extra density could cause the mixture of molten and solid Theia blobs to descend to the core-mantle boundary quickly.

3. We last conducted mantle convection simulations to show that these dense Theia materials can persist atop the core for Earth's entire evolution, ending in two isolated mantle blobs. Their size and calculated seismic velocities align with seismic observations of the two blobs.

This is the whole we have, as shown in this figure: a schematic diagram illustrating the giant-impact origin of the LLVPs.