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Why the Moon Is a Copy of Earth? The Fluidity Clue ⚡ экспресс

Original: "Giant impact between high-viscosity Theia and low-viscosity proto-Earth: Origin of lunar isotopic crisis"
· Wenshuai Liu
arXiv:2606.20398 · 2026-06-18 · CC BY · ⏱ 1 min · Exoplanets
The collision of solid Theia with a liquid Earth explains why the Moon is so similar to our planet.
Abstract

The giant-impact hypothesis explains the birth of the Moon from debris ejected when the planet Theia slammed into proto-Earth. But calculations show over 40% of the disk came from the impactor, while the Moon is chemically similar to Earth (isotopic crisis). The authors suggest accounting for planetary viscosity: small bodies with magma oceans cool faster and become viscous. If Theia was viscous (nearly solid) and proto-Earth was molten, the impact creates a disk mostly from proto-Earth, preserving angular momentum. It's like dropping a hard-boiled egg into a raw one: the solid yolk barely splatters.

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Young Earth was a boiling sphere of liquid rock, while Theia, which crashed into it, had had time to cool and solidify.

It’s like dropping a chunk of cold butter into a pot of soup: the soup splashes out, but the butter barely moves.

Similarly, Earth’s interior spewed into space, forming a cloud of cosmic dust and debris. From this, the Moon gradually coalesced. This hypothesis complements the standard model of the giant impact.

Analysis of lunar soil using light analysis (pioneered by Joseph von Fraunhofer) revealed that the atomic composition of the Moon and Earth is nearly identical. Decades of mystery were solved: due to the difference in fluidity, it was mostly Earth material that escaped into space. The most unexpected outcome: the Moon rocks brought back by the Apollo missions are frozen splashes of our planet. Holding them, you’re touching a shard of ancient Earth.

🎯 That same impact likely tilted Earth’s axis, giving us the seasons. So we have spring and autumn to thank that ancient catastrophe for.

Scientists
Christian DopplerD. B. McLaughlinDidier QuelozMichel MayorR. A. RossiterEmmy Noether
Tags
cosmic dust spectroscopy Standard Model
Laws
Doppler effectNoether's theoremMaxwell's equationsPlanck's lawPlanck–Einstein relationWien's displacement law
Original: arXiv:2606.20398 · CC BY · bridge42worlds