A team of astronomers from the US Naval Research Laboratory in Washington, DC, and the University of Colorado, Boulder, have found evidence of a fine blur of cosmic dust over Mercury & # 39; s orbit, forming a ring about 9.3 million miles (15 million km) wide.
"Scientists never found that there could be a dust ring along Mercury's circuits, which is perhaps why it's gone undetected so far," said lead author Dr. Guillermo Stenborg from the Space Science Division at the Naval Research Laboratory.
"They believed that mercury, unlike Earth or Venus, is too small and too close to the sun to capture a ring. They expected that solar wind and magnetic forces from the Sun would blow excess dust into Mercury's circuits away. "
" We found it by chance, "he added.
Ironically, Dr. Stenborg and his colleagues, Dr. Russell Howard and Dr. Johnathan Stauffer stumbled across the dust ring as they searched for evidence of a dust-free region near the Sun.
At some distance from the Sun, according to a decade of ancient prediction, the mighty heat of the star should evaporate dust, sweeping a whole lot of space. Knowing where this boundary is can tell scientists about the composition of the dust itself and hints on how planets are formed in the young solar system.
So far no evidence of dust-free space has been found, but it is partly because it would be difficult to discover from Earth.
The researchers found that they could solve the problem by building a model based on images of interplanetary space from NASA's Observatory for Solar and Terrestrial Relations (STEREO).
Ultimately, they wanted to test their new model in preparation for NASA's Parker Solar Probe, which is currently flying a very elliptical orbit around the sun.
They wanted to use their technique in the pictures Parker sends back to Earth and sees how dust near the sun behaves.
Two kinds of light emerge in STEREO images: Light from the sun's corona and light reflected by all dust flowing through space. The sunlight reflected from this dust, which slowly circles the sun, is approx. 100 times lighter than coronal lice.
"We are not really dust people. The dust close to the sun only appears in our observations, and generally we have thrown it away," said Dr. Howard.
Mercury dusting was a lucky find, a side discovery made by astronomers while working on their model.
When using their new technique on the STEREO images, they noticed a pattern of improved brightness along Mercury's circuits – more dust, that is, in the light they would otherwise have rejected.
"It wasn't an isolated thing," said Dr. Howard.
"We could see the same 5% increase in dust brightness or density around the sun, regardless of the position of the spacecraft. When that was said, there was something and that is something that stretches around the Sun."
The discovery is described in a document in Astrophysical Journal . Guillermo Stenborg et al. . 2019. Evidence of a circular solar dust ring near Mercury's Orbit.  868, 74; doi: 10.3847 / 1538-4357 / aae6cb