Scientists have discovered that Mercury, the planet closest to our sun, shares its orbit with a large, mysterious dust ring. Another study suggests the ring resembles another ring observed around the planet Venus’s orbit, which scientists believe consists of yet-undiscovered asteroids.
“It’s not every day you get to discover something new in the inner solar system,” NASA astrophysicist Marc Kuchner, a co-author of the Venus study, said in a statement. “This is right in our neighborhood.”
Scientists say both Earth and Venus have pulled in co-orbiting dust rings by their strong gravitational forces. However, they didn’t realize that the same was true of Mercury too. It was previously thought that the closest planet to the sun could be too small to attract a co-orbiting dust ring.
“People thought that Mercury, unlike Earth or Venus, is too small and too close to the sun to capture a dust ring,” solar scientist Guillermo Stenborg of the Naval Research Laboratory in Washington, D.C., said. “They expected that the solar wind and magnetic forces from the sun would blow any excess dust at Mercury’s orbit away.”
The Mercury and Venus studies were published in the Astrophysical Journal and the Astrophysical Journal Letters, respectively. Researchers used photos taken by one of NASA’s twin Solar and Terrestrial Relations Observatory (STEREO) spacecraft. The twins were launched into orbit around the sun in 2006.
Using the photos, researchers were able to build a model which can be used to remove the dust from photos taken by spacecraft. However, their model also enabled them to see the mysterious dust ring around Mercury’s orbit. In fact, there was much more dust than they had expected because it was long believed that the sun’s extreme heat would create a dust-free region around it.
“It wasn’t an isolated thing,” co-author Russell Howard, also a solar scientist at the Naval Research Laboratory, said. “All around the sun, regardless of the spacecraft’s position, we could see the same 5 percent increase in dust brightness, or density. That said something was there, and it’s something that extends all around the sun.”
According to their measurements, the mysterious dust ring close to Mercury measures 9.3 million miles wide. The ring is much smaller than the ring surrounding Venus’ orbit, which is 16 million miles from top to bottom and 6 million miles wide. Venus’ dust ring is not very dense. Scientists estimate that Venus’ ring is only 10% denser than the neighboring dust-free space. Researchers explained in their statement that if all the dust could be combined, it would form an asteroid which measures only 2 miles across.
Kuchner and NASA Goddard astrophysicist Petr Pokorný tried to understand the origin of the dust from Venus’ dust ring, but they couldn’t create a model capable of identifying the origin of the dust particles. They even considered the asteroid belt and larger planets like Jupiter and Saturn as potential sources.
“But none of them worked,” Kuchner said. “So, we started making up our own sources of dust.”
“We thought we’d discovered this population of asteroids, but then had to prove it and show it works,” Pokorný said in the same statement. “We got excited, but then you realize, ‘Oh, there’s so much work to do.'”