moon_earth_size_comparison
Ancient Earth May Once Have Had Many Moonlets
published during a waning gibbous moon.
01/17/2017

For most of us, the moon is simply a fact. It’s always there, changing phases, lighting up the nighttime sky, sometimes even subtly sticking around during the daytime. It elicited inspiration and fear in ancient times—the words “lunacy” and “lunatic” derive from the belief that the lunar cycle made people crazy—and it still arouses everything from curiosity to spirituality to pride in our ability to set foot on it.

But how did the moon get there?

Where did it come from?

When?

Many Moonlets

Artistic depiction of a collision between two planetary bodies to form a moon. Credit: Hagai Perets

Until now, the going theory has been that millions of years ago, Earth collided with another small planet and one of the bigger pieces that broke off got snared in Earth’s orbit and became the moon. Instead, researchers from the Technion-Israel Institute of Technology and the Weizmann Institute of Science have concluded that the current moon isn’t Earth’s first, and that various collisions throughout Earth’s history resulted in the formation of “moonlets” that, under the influence of gravitational attraction, merged with each other to form the moon we see now.

Many Moonlets

Illustration of Earth/moon collision. Credit: NASA/JPL-Caltech

In order to arrive at this hypothesis, researchers relied on 800 computer simulations of celestial bodies crashing into earth. The findings, which were published in Nature Geoscience, support the now widely accepted belief that our planet grew to its present size by retaining material from these impacts.

All of this happened a long time ago. A recent analysis of moonrock gathered during the Apollo 14 mission suggests that our current moon has been around for 4.51 billion years, making it older than previously thought (scientists’ best estimates indicate that the Milky Way formed just 60 million years earlier).

Many Moonlets

Credit: Wikimedia Commons

The impacts that formed the moon would have caused temperatures to spike on Earth, not to mention drastically alter the landscape, so the moon’s older age makes sense given that life on Earth began roughly 4.1 billion years ago—after our planet had a chance to adjust to its new lunar neighbor.