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Earth may have a pair of ‘ghost moons’ made of dust trapped in orbit

Photographs show signs of a ghost moon, a translucent gas cloud that orbits Earth along with our moon. But some say the images are not definitive
A mysterious picture of a moon behind the moon
Earth may have ghost moons, but we’ve yet to see the smoking gun
Curtsinger/National Geographic/Getty

Earth may have a pair of “ghost moons”, translucent clouds of dust that orbit along with our moon. These clouds, which could be up to 100,000 kilometres across, were predicted in 1951, and new pictures seem to show they exist.

The Earth-moon system has a set of five gravitational balance points, where the gravitational forces from Earth and the moon balance out. At these spots, called Lagrange points, objects can get caught, never being pulled down to Earth or the moon.

In 1951, astronomer Józef Witkowski predicted that interplanetary dust should collect at two particular Lagrange points that are each about 400,000 kilometres from Earth and about 400,000 kilometres from the moon, forming equilateral triangles. Then, in 1961, astronomer Kazimierz Kordylewski took the first pictures that seemed to show bright spots near these areas. The collected dust clouds are named Kordylewsi clouds, after him.

But because these clouds are so tenuous and dim, it’s been difficult to observe them definitively, and astronomers have debated if they really do exist. A Japanese spacecraft that flew through the Lagrange points in the early 1990s did not find a clear increase in dust, adding credence to the idea that theses ghost moons may only be theoretical.

But now new pictures appear to capture one of the Kordylewski clouds in impressive detail. Gábor Horváth at Eötvös Loránd University in Hungary and his colleagues took pictures of one of these ghostly satellites using filters designed specifically to pick up light that’s been bounced around by dust grains.

A picture of the area where there may be a ghost moon
One of the new pictures. The position of the Lagrange point is shown by a white dot. The central region of the Kordylewski dust cloud is visible in bright red pixels and the straight tilted lines are traces of satellites.
J. Slíz-Balogh

They found lots of this polarised light in the area where we’d expect one of the Kordylewski clouds to be. Their observations match patterns seen vaguely in earlier, lower-quality images. “We are sure that these clouds are there,” says Horváth.

Nevertheless, some other astronomers are not convinced that these observations actually show any difference from the surrounding areas. “Rather than a ‘smoking gun’, this latest paper seems to be more like the smell of gunsmoke,” says Anthony Dobrovolskis at the SETI Institute in California.

Monthly Notices of the Royal Astronomical Society

Topics: Moons / Solar system