SHOCKING! Scientists propose revolutionary theory for Moon's origin, challenge popular collision hypothesis
By Sunita Iyer | First Published Nov 13, 2024, 7:45 AM ISTA new theory proposes that Earth's Moon may have been captured through binary-exchange capture, offering an alternative to the traditional impact hypothesis and explaining various orbital and chemical anomalies.
For centuries, scientists have debated how Earth's Moon came to be, with the most widely accepted explanation being a catastrophic collision with a protoplanet named Theia. But now, a groundbreaking new theory from Penn State University suggests that the Moon may not have formed from a violent impact after all. Instead, researchers propose that Earth might have captured the Moon through a process called binary-exchange capture, a radically different idea that has intrigued experts.
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Lead researcher Professor Darren Williams and his team have put forward the hypothesis that the Moon could have originally been part of a 'terrestrial binary' - pair of rocky objects orbiting one another in space. As this binary system passed close enough to Earth, the gravitational pull of our planet could have snatched the Moon into orbit, while the second body was sent hurtling into space.
"No one knows how the moon was formed. For the last four decades, we have had one possibility for how it got there. Now, we have two," Williams said.
Traditional Impact theory vs binary-exchange capture
In 1984, scientists convened at the Kona Conference in Hawaii to reach a consensus on the Moon’s origins. By analyzing the 800 pounds (363 kilograms) of lunar material brought back by NASA’s Apollo missions, they discovered that the Moon’s chemical composition closely resembled Earth’s, though with some differences. Based on this evidence, they concluded that the Moon was likely formed from debris ejected when a celestial body collided with the early Earth.
This impact theory gained widespread support because it aligned well with what was known about the Moon’s chemical makeup. However, it doesn't account for all the details. For instance, Professor Williams and his co-author point out that if the Moon had formed from a ring of debris that gradually condensed into a sphere, we would expect it to orbit more closely to Earth's equator.
However, the Moon’s orbit is actually tilted about seven degrees relative to Earth’s equator, which contradicts the expectations of the impact theory. To explain this anomaly, the researchers turned to a phenomenon known as binary-exchange capture.
This theory proposes that Earth may have captured one of a pair of passing rocky bodies, pulling it into orbit as its satellite. Professor Williams cites the example of Triton, Neptune's largest moon, as evidence for this idea. Current theories suggest that Triton was captured from the Kuiper Belt, where one in every ten objects is thought to be part of a binary system. Like our Moon, Triton orbits Neptune at a highly tilted angle, with its orbit leaning 67 degrees away from Neptune’s equator.
Mathematical models support new theory
According to mathematical models, it is entirely plausible that a similar event could have occurred with our moon.
In their paper, published in The Planetary Science Journal, the researchers calculate that Earth could have captured an object ranging from 1 to 10 percent of its total mass.
At just 1.2 percent of Earth's mass, the moon fits well within this range.
The only condition is that the planetary binary would have had to pass within 80,000 miles (128,750 km) of Earth at a speed under 6,700 miles per hour (10,800 km/h).
While this might sound incredibly fast, in the vast scale of the solar system, it's actually the equivalent of a leisurely stroll.
The issue is that, even at these relatively slow speeds, when the moon first arrived, its orbit would have been highly elliptical, similar to that of a comet around the sun.
However, the researchers also demonstrate how this orbit would have changed under the influence of tidal forces.
As the moon orbited Earth, the tides would have lagged slightly behind its motion, creating a gravitational pull that gradually worked to stabilize its erratic orbit.
Over thousands of years, this constant tug would have gradually made the orbit more circular and regular, eventually settling into the close orbit it holds today.
"Today, the Earth tide is ahead of the Moon, high tide accelerates the orbit. It gives it a pulse, a little bit of boost. Over time, the Moon drifts a bit farther away," Professor Williams said.
Currently, the moon is so distant that both the Sun and Earth exert gravitational pulls on it, causing it to drift about 3 cm further away each year.
Implications for understanding the moon's origin
This theory offers key advantages, as it explains the moon's tilted orbit and accounts for the presence of certain chemical isotopes found on the moon but not on Earth.
The researchers acknowledge that their theory would be difficult to prove and depends on several "implausible events" occurring simultaneously.
Nevertheless, Professor Williams asserts that binary-exchange capture remains a viable alternative to the traditional collision theory and one that deserves further exploration.
The researchers suggest that planetary binaries may have been more common in the early solar system and could have feasibly contributed to the formation of the moon.
"This opens a treasure trove of new questions and opportunities for further study," Professor Williams concluded.
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