The Curious Case of Earth’s Extra Moon

By: Ben Campbell | Last updated: Jul 08, 2024

Several years ago, astronomers believed they had made a groundbreaking discovery when they proposed that the Earth had a second, much smaller Moon.

Researchers observed a small celestial body known as 469219 Kamo’oalewa, which stood out as it remained close to Earth over many orbital periods, just like the Moon. Further investigation revealed that Kamo’oalewa was a near-Earth asteroid (NEA) and a quasi-satellite of Earth.

The Discovery of Kamo’oalewa

The celestial object 469219 Kamo’oalewa was first spotted by astronomers back in 2016. Researchers observed it shared the same orbit as Earth, leading many to suggest it could be a second moon.

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The Paranal Observatory of European Southern Observatory shooting a laser guide star

Source: Wikimedia

Further research using powerful telescopes concluded that while Kamo’oalewa’s orbit is strikingly similar to Earth’s, it’s different enough to dismiss the second moon hypothesis, much to the scientific community’s disappointment.

Kamo’oalewa Deemed a Near Earth Asteroid

After collecting data on its orbital characteristics and conducting spectral analysis, researchers determined that Kamo’oalewa was actually a near-Earth asteroid and a quasi-satellite of our planet.

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A small asteroid flying through space

Source: Wikimedia

According to the BBC, it’s anywhere from 40 m to over 100 m wide, meaning it’s about the size of the Statue of Liberty.

Kamo’oalewa Follows Earth's Orbit Around the Sun

Like the Moon, Kamo’oalewa remains close to our planet over many orbital periods and will likely continue to do so for several centuries.

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A photograph of the Sun shining above the Earth in space

Source: Wikimedia

While it gives off the impression that it circles the Earth, researchers have confirmed it does not. However, its orbit around the sun aligns with our planets.

Scientists Come up With Origin Theory

Astronomers were left with one question: where did this unique celestial body come from? Now, they believe they have their answer.

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Two scientists pictured speaking at their desk

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In 2021, a team of scientists at the University of Arizona had been observing Kamo`oalewa using powerful telescopes when they realized the asteroid was relatively similar to lunar rock brought back from the Apollo missions.

Dislodged From the Moon

The scientists later theorized that Kamo’oalewa may have been dislodged from the moon at some point in the distant past after a meteorite smashed against its surface.

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A photograph of a full moon

Source: APHOTOGRAFIA/Getty Images

Scientists strongly believe the asteroid is made from space-wetted silicates, which is also the material that makes up the body of our moon.

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New Research Confirms Findings

Another group of astronomers recently published new findings in the peer-reviewed journal Nature Astronomy, which further supports the idea that Kamo’oalewa came from the moon.

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The data, published this past April in Nature Astronomy, suggests Kamo’oalewa likely broke off from the Giordano Bruno crater due to the asteroid’s unique shape and size.

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Researchers Find the Likely Source

According to the researchers who participated in the study, they believe they’ve found the scar left behind by the enormous impact that dislodged Kamo’oalewa from the moon.

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A photograph of a crater on the moon

Source: Wikimedia

They suggest that the far side crater, Giordano Bruno, named in honor of the 16th-century Italian cosmological theorist, appears to be the “likely” source.

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How the Researchers Came Across the Evidence

Speaking on the new evidence, Phys.org broke down how the team of international scientists came to their conclusion.

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A photograph of the researchers working at a desk

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“The team began by creating a computer model to mimic the type of collision that could have resulted in a piece of the moon’s surface the size of Kamo’oalewa being flung into space. In so doing, they were able to estimate the likely size of the asteroid that would have struck the moon, and from that, the size of the crater it would have left behind,” they wrote.

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Research Team Shortlists Potential Craters

After this, the team began shortlisting several potential craters that matched Kamo’oalewa’s theorized origin.

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A photograph of a crater on the moon

Source: Wikimedia

They then compared samples of moon material brought back to Earth that had been found near one prime possibility, the Giordano Bruno crater. They found spectral similarities between the samples and the asteroid Kamo’oalewa,” wrote Phys.org.

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Space Probe Aims to Conclude the Team's Hypothesis

As things stand, it appears the mysterious origins of Kamo’oalewa have been solved. However, several space probes will soon test the team’s hypothesis.

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A photograph of a space probe

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The first is the Chinese Tianwen-2 mission, which is set to launch in 2025. This probe will collect a sample of the asteroid and bring it back to Earth for further testing.

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The Earth’s Stuck With One Moon

The second miss will come in 2027, when NASA launches its NEO Surveyor space telescope, which will provide further information on the asteroid’s orbit.

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A photograph of a full moon above the Sierra Nevada mountain range beside Lake Tahoe

Source: George Rose/Getty Images

Even with this, the group of astronomers who recently published the new data are almost certain of Kamo’oalewa’s lunar origin. But unfortunately, it should not be regarded as a second moon.

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