Astronomie - Existence of mysterious dust clouds close to Earth cautiously confirmed


Astronomers may have captured images of a mysterious, hard to spot dust cloud just 400,000 kilometres away, 60 years after it was originally predicted. Ben Lewis reports.


In this picture the central region of the Kordylewski dust cloud is visible in the form of  bright red pixels around the L5 Lagrange point. The straight tilted lines are traces of satellites.


A controversial 60-year-old idea has shot into the realms of possibility, thanks to new observations of one, and potentially a second, ghostly dust cloud orbiting just 400,000 kilometres from Earth.

The clouds were first reported by Polish astronomer Kazimierz Kordylewski in 1961, but their extreme faintness makes them difficult to detect and many scientists doubted their existence.

Now, new observations published in the Monthly Notices of the Royal Astronomical Society by a team led by Judit Slíz-Balogh from the Eötvös Loránd University in Hungary have reignited the possibility of their existence.

The dust clouds are formed by a peculiar interaction between the gravities of Earth and the moon.

While large bodies gravitationally draw matter towards themselves, there are five points around Earth where the respective gravitational pull of two large objects – either the Earth, Moon, Sun or another planet – is balanced with the centrifugal force experienced by smaller orbiting objects. This balance means that that objects can become trapped and be held in relative position, called Lagrange points.

Two of these points, L4 and L5, form equilateral triangles with the Earth and the moon, and move around the Earth with the moon’s orbit. While they aren’t completely stable – being perturbed slightly by the sun, they nevertheless form points where interplanetary dust might collect, at least temporarily.

Indeed, it was at L5 where Kordylewski observed two clusters of dust in 1961. However, they were so difficult to see that their confirmation remained in contention.

Slíz-Balogh and the team began by creating a three-dimensional model consisting of the sun, Earth, moon and a cloud of dust, finding that the formation of such a cloud is possible at L5.

The researchers then moved to Slíz-Balogh’s private observatory in the small Hungarian town of Badacsonytördemic, using a linearly polarising filter system to attempt to observe the phenomenon.

The images they captured show polarised light reflected from dust, extending well outside the field of view of the camera lens – matching predictions from their simulation and those of Kordylewski nearly 60 years earlier.

“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,” the team write.

Adds Slíz-Balogh: “The Kordylewski clouds 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. It is intriguing to confirm that our planet has dusty pseudo-satellites in orbit alongside our lunar neighbour.”

However, despite the successful observations and modelling, the results aren’t conclusive. Previous studies from other researchers have also been contradictory about the clouds’ presence, with the Hungarian team accepting that the they may be transient, and could be blown away by solar winds or by gravitational perturbations from the Sun or other planets.

Indeed, the team’s own modelling suggests the structure and density of the particles is inconsistent, with a continuously changing, pulsing, and whirling shape.

Lagrange points have also been observed between the sun and Jupiter, Earth, Mars and Neptune systems, often with small celestial objects “parked” within them. However, around Earth the locations have piqued interest as potential staging locations for satellites.

NASA has used the L1 position around Earth, with its uninterrupted view of the sun, as a holding position for its Solar and Heliospheric Observatory (SOHO). L2 is expected to be used as a staging position for the yet to be launched James Webb Telescope.

Quelle: COSMOS

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