They were first theorized in the 1700s, predicted in the 1950s and finally confirmed in October 2018 … appropriately in time for Halloween. We’re talking about ‘ghost moons’ and their existence between Earth and the Moon shows just how much gravitational pull these two bodies have on each other and the space between them. Should we be scared of these ‘ghosts’? Should the Earth or the Moon?
This celestial ghost story begins in 1767 when Swiss mathematician Leonhard Euler predicted the existence of three Lagrangian points – positions between two space objects where their gravitational pull alone can hold a smaller object in a constant position between them – between Earth and the Moon. Their name comes from Italian mathematician and astronomer Joseph-Louis Lagrange who predicted two more in 1772 and wrote a definitive paper about them. Now called L1 through L5, they are used by NASA to position space observatories for stable, uninterrupted views of the Sun and deep space.
Could the Lagrange points hold something even less substantial than a satellite yet occupying enough space to be considered a ‘ghost moon’? That question was pondered by Polish astronomer Kazimierz Kordylewski in the 1950s. In 1961, he claimed to have discovered evidence pointing to two nonmoving dust clouds at L5 in 1961. They picked up the name Kordylewski clouds for obvious reasons but have never actually been confirmed due mostly to lack of interest by other astronomers. That changed recently when astronomers from Eötvös Loránd University in Budapest, Hungary, and a second team from Moscow University in Russia found the clouds … at least for a while.
A two-part paper in the Monthly Notices of the Royal Astronomical Society and reviewed by Gizmodo explains how the Hungarian astronomers used a computer simulation to model a probable dust cloud at LaGrange point L5. This effort was duplicated by the Russian team and published in Acta Astronautica. Study co-author Judit Slíz-Balogh has a private observatory in Badacsonytördemic, Hungary, with special lenses that measure the orientation of a light’s electric field (its polarization) as it travels through space. After waiting months for a clear night (Why build an observatory in such a poor location? Asking for a friend), they hit two consecutive ones and got their confirmation polarization.
Or did they? The review in Gizmodo points out that other observatories pointed at the same point haven’t seen cloud evidence, suggesting that this Kordylewski cloud is transient and gets wiped out periodically by solar wind. Slíz-Balogh and the Hungarian team stick by their evidence and say there’s a second cloud at L4 as well.
Needless to say, Kazimierz Kordylewski, Leonhard Euler and Joseph-Louis Lagrange would be thrilled to know that their theories and predictions have been proven correct and their names are in the news again. They’d probably be tweeting away at #ghostmoonsexisttoldyouso.