Astronomers Have Discovered A Dust Ring Around The Orbit Of Mercury

Extremely Not to scale impression of the dust rings in the inner Solar System. NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith

The Solar System is dusty. So dusty that given the right conditions you can see it with the naked eye as a faint triangular glow just before sunset or sunrise. Earth moves through a ring of dust in its orbit, as does Venus. Now astronomers have discovered that Mercury’s orbit sports a ring as well.

In a study published in The Astrophysical Journal, researchers admit that they found the ring while looking for the exact opposite. They were collecting evidence for the existence of a dust-free region near the Sun, as it is expected that the Sun would vaporize any dust in its vicinity or push it further out.

Since it’s not possible to look for this region from Earth, the team employed the combined power of NASA’s STEREO satellite and the Parker Solar Probe to measure the dust around the Sun. Usually, the dust signal is just noise and discarded, but not in this case. Instead, the team saw a donut of dust in Mercury’s orbit. The ring is 15 million kilometers (9.3 million miles) wide. Mercury itself is only 4,880 kilometers (just over 3,000 miles) across.

“We found it by chance,” lead author Guillermo Stenborg, from the Naval Research Laboratory, said in a statement. “People thought that Mercury, unlike Earth or Venus, is too small and too close to the Sun to capture a dust ring. They expected that the solar wind and magnetic forces from the Sun would blow any excess dust at Mercury's orbit away.”

Another new study has important implications for the dust in the inner Solar System. It appears the dust ring around Venus might not have formed like Earth’s one, from the dust and debris of collisions further out. The new research suggests that asteroids in the orbit of Venus might be the cause of it.

As reported in The Astrophysical Journal Letters, researchers attempted to model the formation of the ring with any known or expected cause: asteroid belt impacts, Halley-type comets, Jupiter-family comets, and even very distant Oort cloud comets, but none of them could explain the ring.

The team then looked at another possibility. Could it be caused by never-before-detected asteroids near Venus itself?

Models strongly suggest that this is indeed the case but it raised another problem on how the asteroids ended up there. The most likely hypothesis is that they formed there and survived from the beginning of the Solar System. In their model, 8 percent of the asteroids survived the 4.5 billion years since the planet formation. The next challenge is now proving that these asteroids actually exist.

"If there's something there, we should be able to find it," Petr Pokorny from NASA's Goddard Space Flight Center Goddard said.

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