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A team of astronomers from the US Naval Research Laboratory in Washington, DC, and the University of Colorado, Boulder, has highlighted a thin cloud of cosmic dust on the orbit of Mercury, forming a ring 15.3 km wide. .
In this illustration, several rings of dust surround the sun. These rings are formed when the gravities of the planets bring back grains of dust in orbit around the Sun. Image credit: NASA / Mary Pat Hrybyk-Keith Goddard Space Flight Center.
"Scientists have never thought that a ring of dust could exist along Mercury's orbit. This may be the reason why it has not been detected so far, "said Dr. Guillermo Stenborg, lead author, Space Science Division, Naval Research Laboratory.
"They thought that Mercury, unlike Earth or Venus, is too small and too close to the Sun to capture a ring. They expected the solar wind and the magnetic forces of the Sun to drive excess dust into Mercury's orbit. "
"We found it by chance," he added.
Ironically, Dr. Stenborg and his colleagues, Dr. Russell Howard and Dr. Johnathan Stauffer, came across the ring of dust while they were looking for evidence of a dust-free region close to the Sun. .
According to a decades-old prediction, some distance from the Sun, the star's powerful heat should vaporize the dust, sweeping an entire space. Knowing where this limit is can help educate scientists about the composition of the dust itself and how the planets formed in the young solar system.
Until now, no evidence of dust-free space has been found, but that's partly because it would be hard to detect from the Earth.
The researchers thought they could work around this problem by building a model based on images of the interplanetary space of NASA's solar and terrestrial observatory (STEREO).
In the end, they wanted to test their new model for NASA's Parker solar probe, which is currently operating in a highly elliptical orbit around the Sun.
They wanted to apply their technique to the images that Parker will send to Earth and observe the behavior of dust near the Sun.
Two types of light appear in STEREO images: the light of the solar corona and the light reflected by all the dust floating in space. The sunlight reflected by this dust, which rotates slowly around the Sun, is about 100 times brighter than the coronal lumen.
"We are not really dusting people up. The dust near the Sun appears in our sightings and, in general, we threw it, "said Dr. Howard.
Mercury's dust ring was a find, a discovery that astronomers made while working on their model.
When they used their new technique on STEREO images, they noticed an increased pattern of brightness along Mercury's orbit – more dust, that is, they had otherwise planned to remove.
"It was not an isolated thing," Dr. Howard said.
"All around the Sun, regardless of the position of the spacecraft, we could see the same 5% increase in brightness or density of dust. That said something was there, and something is spreading all around the Sun. "
The discovery is described in an article from Astrophysical Journal.
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Guillermo Stenborg et al. 2019. Proof of a ring of circular dust around the orbit of Mercury. ApJ 868, 74; doi: 10.3847 / 1538-4357 / aae6cb
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