A ghostly dust satellite or two might be orbiting the Earth, according to new research building on a 60-year-old idea. Massive objects attract one another through the force of gravity. But when you have multiple huge objects with just the right masses, their mutual gravitational field can introduce some anomalies — like gravitational points that can hold things stable.
Scientists have found objects orbiting in these "Lagrange points" created by the combined gravity of the Sun and Mars, the Sun and Neptune, and the Sun and Jupiter. Researchers are now reporting evidence of dust clouds, called Kordylewski dust clouds, in the Lagrange points created by the Earth and the Moon.
Swiss mathematician Leonhard Euler predicted the first three Lagrange points in these kinds of systems in 1767, and Italian astronomer-mathematician Joseph-Louis Lagrange predicted two more points back in 1772. Today, scientists know all about them — NASA's upcoming James Webb Space Telescope will orbit the Sun and Earth in a stable Lagrange point called L2.
The Earth and Moon have the right ratio such that some amount of mass could stably orbit the system at L4 and L5, the two Lagrange points actually discovered by Lagrange himself. Polish scientist Kazimierz Kordylewski observed evidence of dust clouds near L5 in 1961.
Since then, there hasn't been much research into these dust clouds. But in the past two months, teams of scientists have taken on an investigation to see whether these clouds could exist, despite the additional gravity of the Sun or its solar winds potentially blasting such a cloud away.
The team from Eötvös Loránd University began by building a mathematical simulation, based on the equations of a system containing the Sun, Earth, Moon, and a fourth dust cloud. They found that a swirling, ever-changing dust cloud was totally possible at L5, according to the first of two papers in the Monthly Notices of the Royal Astronomical Society.
This confirmed another analysis from a team of Russian scientists published a month before.
But would they actually see a Kordylewski cloud? The team set out using study author Judit Slíz-Balogh's private observatory in Badacsonytördemic, Hungary, with special lenses that could measure the polarisation of the light — essentially, the orientation of its corresponding electric field as it travels through space. They hoped that they'd be able to see the Kordylewski dust cloud's signature on the polarisation of light coming from L5.
They found it, but not without effort. "After several-months of perseverance (because it is hard to find moonless and cloudless good nights in Hungary) we succeeded in catching the [Kordylewski dust cloud] around the L5 Lagrange point on two consecutive nights," they wrote in the second paper published in the Monthly Notices of the Royal Astronomical Society.
Though the team has the modelling and observation to back it up, it's still worth treating their conclusion with a grain of salt. According to the paper, their observations may be a transient phenomena, and whatever dust they saw might easily be blown away through gravitational jostling from other planets or solar wind.
Plenty of other telescopes, as well as a Japanese probe, haven't found evidence for the dust — though other observations have. Maybe it's something else, though the researchers took great care to rule out any other potential sources of this polarised light. The researchers argue that their polarisation-observing method offered a better way to find the dust cloud.
So, is the cloud really there? The newest evidence points to yes — and if it really is there, that means that we have at least one, if not two, ghost moons, with another possible dust cloud at L4. Spooky!