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Earth Has Two Hidden Moons, but They Are Not What You Might Expect

Earth Has Two Hidden Moons

Imagine looking up at the sky and seeing not one but three moons! While many planets in our solar system have multiple moons, Earth has only one, or so we thought. For over half a century, scientists have asked the question, “Are there more natural satellites orbiting the Earth, or is it just the one moon (known the “Moon” or “Luna”) that is visible to us? After decades of controversy and speculation, a team of Hungarian physicists and astronomers may have finally found the answer. According to them, Earth has two additional moons that are made entirely of dust.

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The “dust moons” were first observed in 1961, and they are thought to exist 250,000 miles away.

Moon
This view from the Apollo 11 spacecraft shows the Earth rising above the moon’s horizon. Image credits: NASA

The search for additional moons began as far back as the 19th century. Though there have been several likely candidates, none of them were confirmed. For example, certain NEOs, or near-Earth objects, share orbital resonance with our planet. These objects are often dubbed as “second moons.” An asteroid called “469219 Kamoʻoalewa” is thought to be the planet’s most stable quasi-satellite. Discovered back in 2016, the asteroid circles around Earth as it orbits around the Sun. Though it is too far away to be called a satellite of Earth, it can be classified as a NEO, or “quasi-satellite.”

The “dust moons,” on the other hand, seem to be different from these near-Earth objects. When describing their findings which were published in the peer-reviewed scientific journal called Monthly Notices of the Royal Astronomical Society, the Hungarian scientists stated that they were able to take photos of the strange “pseudo-satellites” that exist roughly 250,000 miles away. That is about the same distance between Earth and the Moon.

Though many researchers previously inferred their existence, the dust clouds were not seen until 1961. A Polish astronomer named Kazimierz Kordylewski first saw them. The clouds were later named after him.

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Difficult to find, the Kordylewski Clouds cover a large expanse of space. Scientists believe its size is 65,000 by 45,000 miles.

Dust cloud
Artist’s concept of a Kordylewski cloud in the night sky at the time of the observations. The brightness is greatly enhanced; we wouldn’t really see this cloud. Image credits: G. Horváth/Royal Astronomical Society

The Kordylewski Clouds, situated at two Lagrange points in the planet’s orbit, are almost the same distance away as the Moon, but they mostly go unnoticed by astronomers. However, just because these dusty, pseudo-satellites are generally overlooked, it does not mean they are inferior in size. Each cloud is thought to be 15 by 10 degrees in width. The clouds cover a large area of 65,000 by 45,000 miles, which is approximately nine times wider than the planet Earth! Although the clouds are enormous, they are made of very tiny particles. When the sunlight bounces off of these particles, they glow slightly.

The clouds are thought to be ancient, and they have managed to remain hidden all this time because they are faint and hard to detect against other light sources such as the zodiacal light, starlight, galactic light, and sky glow. Now, the researchers have used special polarizing filters to capture the scattered light that bounces off of the tiny particles within the clouds. Their model has also revealed that solar wind can easily blow away the smooth dust particles. If that happens, dust particles from other objects, such as comet trails, can fill up the dust clouds again. That means even though the clouds barely move, they are constantly changing.

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Kordylewski was the first to research the Lagrange points in search of additional moons. Instead of finding a solid-body satellite like the Moon, he happened upon the dusty clouds.

Earth-Moon System
Diagram showing the Lagrangian points of the Earth-Moon system. Kordylewski clouds exist in the regions of L4 and L5. Image credits: NASA

As mentioned above, scientists have speculated for decades that Earth may have additional moons. They also proposed that any additional moon would be found at any of five specific points in deep space. Known as Lagrange points, these locations are famous as orbital “sweet spots.” Here, the gravitational force between two large celestial objects such as the Sun and Earth or the Moon and Earth gets balanced out due to the centripetal force of their respective orbits. At Lagrange points, smaller objects stay stuck in fairly stable positions while maintaining a safe distance from Earth and the Moon.

Kazimierz Kordylewski
(Image 1) Kazimierz Kordylewski (Image2) Lagrange Points of the Earth-Sun system. Image credits: Kokorik /Wikimedia, NASA

Back in the 1950s, Kordylewski first looked into L4 and L5 (Lagrange points 4 and 5) in search of additional solid-body moons. Instead, he discovered the first signs of the dusty clouds. From the zodiacal band to meteor showers and comets, all contribute to our solar system being fairly dusty. Under the right conditions, any keen sky-watchers can spot clouds of particles scattered between planets. However, the Kordylewski Clouds are different from the other dusty features. They are not stable, and the dust particles are constantly replaced. That makes the dusty clouds both ancient and ever-changing at the same time.

Dust particles get stuck because of the Lagrange effect, but then they escape whenever there is a slight tug from the Moon or Earth. To replenish the vacuum, the clouds then draw dust from meteor showers and other interplanetary particles.

Similar to cosmic tumbleweeds, these dusty clouds may have a significant impact on the future of space exploration.

Dust moon
In this image, the central region of the Kordylewski dust cloud is visible (bright red pixels). The straight tilted lines are traces of satellites. The L5 point in white is the Earth-moon L5 Lagrange point. Image credits: Judit Slíz-Balogh/Royal Astronomical Society

These dusty clouds, which act like cosmic tumbleweeds, may influence future space explorations. For example, the Lagrange points are thought to be excellent locations where satellites or space stations can be parked. Because of the unique characteristics of these points, the objects will remain in orbit without needing to use too much fuel. The James Webb Space Telescope, the planned successor to the Hubble Space Telescope, is set to be launched in 2020. Its planned location is Lagrange point L2. Some agencies have also theorized that the Lagrange points can be used as transfer stations when traveling to Mars.

The discovery of the “dusty moons” may not seem like much, at least not when you compare it to the mental image of having two additional, solid-body moons orbiting Earth. However, you must think about how this discovery was made possible after 50 years of mathematical and astronomical work. It should also make you wonder about all the other gems that may be hiding away in our solar system.

(Sources: 1, 2, 3, 4)

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