Earth’s unusually large Moon may have formed in just five hours following a cataclysmic collision with a Mars-sized protoplanet named Theia, according to new high-resolution computer simulations published in The Astrophysical Journal Letters. The findings reshape the long-standing giant impact hypothesis by demonstrating that the physical strength and temperature of early planetary bodies played a critical role in how the satellite was born.
How Material Strength Changes the Giant Impact Hypothesis
Researchers modeled the birth of the Moon by treating early Earth and Theia primarily as fluids. According to studies led by the Southwest Research Institute (SwRI) and the University of Arizona, those early models assumed the 4.5-billion-year-old collision was violent enough to melt and vaporize large portions of both worlds, rendering their internal geology irrelevant.
Adeene Denton and co-authors challenged that assumption by incorporating material strength and temperature-dependent rock behavior into Smoothed Particle Hydrodynamic (SPH) simulations. “When you simulate the Earth and the moon as colliding bodies with [different] geologic properties, it changes how the moon forms out of that impact—that’s something we considered unnecessary before,” Denton said in a statement.
Did you know? While the stresses deep inside Theia were immense, the physical strength of its outer rocky layers resisted deformation upon impact, altering the momentum-transfer process that built our night sky’s companion.
Why Temperature Dictates the Five-Hour Moon Formation Timeline
Temperature serves as the primary driver of material strength in planetary collisions. Because early planets were much hotter shortly after the solar system formed, their rocky mantles were softer and more malleable.
When researchers tested varying thermal states, extreme scenarios involving hotter, weaker planets produced an intact Moon within approximately five hours. Conversely, colder initial conditions favored the creation of a massive disk of debris that slowly accreted into the Moon over extended periods. “Depending on how hot the Earth and Moon are before the collision, the impact can destroy Theia and produce this massive disk of debris that eventually forms the Moon,” Denton noted. “But when we used the same parameters as original impact modeling, down to the equal temperature structures inside both bodies, within around five hours, an intact Moon emerged.”
Unresolved Mysteries in Lunar Evolution
Despite refining the timeline of lunar origins, scientists note that current models still leave major questions unanswered. Most notably, Apollo mission rock samples show that Earth and the Moon share remarkably similar chemical and isotopic compositions, a puzzle that standard impact models have yet to fully resolve.
To address this, Denton proposed that Earth and Theia may have formed from the same region of the early solar system, whereas Mars developed with a distinct composition from a more distant location. Robin Canup, a pioneer of giant impact modeling who was not directly involved in the new study, emphasized that the findings bridge a crucial gap. The results “imply a potential connection between the physical properties of the Moon today and the thermal state of the Earth and Theia at the time of the giant impact,” Canup stated.
Frequently Asked Questions
How old is the Moon according to current scientific data?
Lunar samples collected during NASA’s Apollo missions indicate that the Moon is approximately 4.5 billion years old, placing the impact roughly 100 million years after the formation of the sun.
Did the Moon actually form in five hours?
The simulations do not prove the Moon formed in five hours definitively; rather, they demonstrate that rapid assembly is physically possible when the material strength and temperature of early planets are factored into collision physics.
What was Theia?
Theia is a long-lost, Mars-sized protoplanet that scientists believe collided with early Earth approximately 4.5 billion years ago, triggering the formation of the Moon.
What are your thoughts on these new planetary simulations? Do you think the Moon formed in a matter of hours or through gradual debris accretion? Leave a comment below, share this article with fellow space enthusiasts, and subscribe to our newsletter for more updates on planetary science.
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