A research team from Hungary has confirmed the existence of two enigmatic celestial objects called Kordylewski dust clouds (KDCs) — large concentrations of dust positioned around the L4 and L5 Lagrangian points of the Earth-Moon system.
An artist’s impression of the Kordylewski dust cloud in the night sky. Image credit: Gábor Horváth.
The Earth-Moon system has five points of stability where gravitational forces maintain the relative position of objects located there.
Two of these so-called Lagrange points, L4 and L5, form an equal-sided triangle with the Earth and Moon, and move around the Earth as the Moon moves along its orbit.
L4 and L5 are not completely stable, as they are disturbed by the gravitational pull of the Sun. Nonetheless they are thought to be locations where interplanetary dust might collect, at least temporarily.
In 1961, Polish astronomer Kazimierz Kordylewski found two bright patches near the L5 point, which might refer to an accumulation of dust particles, with various reports since then, but their extreme faintness makes them difficult to detect and many scientists doubted their existence.
In new research, Eötvös Loránd University scientist Gábor Horváth and colleagues modeled KDCs to assess how they form and how they might be detected.
They were interested in their appearance using polarizing filters, which transmit light with a particular direction of oscillation, similar to those found on some types of sunglasses.
Scattered or reflected light is always more or less polarized, depending on the angle of scattering or reflection.
The team then set out to find the dust clouds. With a linearly polarizing filter system attached to a camera lens and CCD detector at a private observatory in Hungary (Badacsonytördemic), the researchers took exposures of the purported location of KDC at the L5 point.
Pattern of the angle of polarization of the sky around the L5 Lagrange point of the Earth-Moon system, measured by imaging polarimetry in the green (550 nm) spectral range at 01:14 GMT on August 19, 2017. The position of the L5 point is shown by a white dot. In this picture the central region of the Kordylewski dust cloud is visible (bright red pixels). The straight tilted lines are traces of satellites. Image credit: Judit Slíz-Balogh.
The images they obtained show polarized light reflected from dust, extending well outside the field of view of the camera lens.
The observed pattern matches predictions made by the same group of researchers in an earlier paper and is consistent with the earliest observations of KDCs six decades ago.
The astronomers were able to rule out optical artifacts and other effects, meaning that the presence of the dust cloud is confirmed.
“KDCs are two of the toughest objects to find, and though they are as close to Earth as the Moon are largely overlooked by researchers in astronomy,” said team member Dr. Judit Slíz-Balogh, of the Eötvös Loránd University.
“It is intriguing to confirm that our planet has dusty pseudo-satellites in orbit alongside our lunar neighbor.”
The research is published in two papers in the Monthly Notices of the Royal Astronomical Society.
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Judit Slíz-Balogh et al. 2018. Celestial mechanics and polarization optics of the Kordylewski dust cloud in the Earth–Moon Lagrange point L5 – I. Three-dimensional celestial mechanical modelling of dust cloud formation. MNRAS 480 (4): 5550-5559; doi: 10.1093/mnras/sty2049
Judit Slíz-Balogh et al. 2018. Celestial mechanics and polarization optics of the Kordylewski dust cloud in the Earth–Moon Lagrange point L5 – Part II. Imaging polarimetric observation: new evidence for the existence of Kordylewski dust cloud. MNRAS 482 (1): 762-770; doi: 10.1093/mnras/sty2630
