Science & Technology

Astronomers Discovered a Huge Ring of Dust Hogging Mercury's Orbit

The sun's innermost planet has a very dusty mystery. Scientists just found a ring of dust more than 9 million miles wide sharing Mercury's orbit, which they didn't think was possible. It's also not the only one.

Dust in the Wind

The solar system used to be just gas and dust, and then over time, little nodules of the stuff collected and grew under their neighbors' gravity. From dust particles and gas blobs grew asteroids and comets, then small planets, and then — where enough material was available — very large worlds.

Scientists stumbled across the dust ring while building a model based on pictures from NASA's Solar and Terrestrial Relations Observatory spacecraft, or STEREO. Their goal was to help a newer satellite, the Parker Solar Probe, take better images of dust near the sun.

Artist's illustration showing several dust rings circling the sun, formed by the gravitational tugs of orbiting planets. Recently, scientists discovered a dust ring at Mercury's orbit and concluded that Venus' ring likely originates from a group of as-yet-undiscovered co-orbital asteroids.

Their original objective was to remove the light reflected off of that dust, known as "dust shine," to help get clearer images, but this led to a larger question: Just how much dust is really there? While playing around with the STEREO images, they saw "a pattern of enhanced brightness," as NASA called it, along the orbit of Mercury.

"It wasn't an isolated thing," said Russell Howard, a co-author and solar scientist at the Naval Research Laboratory in Washington, D.C., in a NASA statement. "All around the sun, regardless of the spacecraft's position, we could see the same five percent increase in dust brightness, or density. That said something was there, and it's something that extends all around the sun."

This ring was a huge surprise. Scientists thought that the constant stream of charged particles from the sun known as the solar wind, along with the sun's magnetic forces, would push the dust far beyond Mercury's orbit. But it looks like tiny Mercury was just big enough for its gravity to capture this dust and hold it in place.

The research was published in The Astrophysical Journal in November 2018 and highlighted on NASA's website this week. The lead author was Guillermo Stenborg, also of the Naval Research Laboratory and currently located at the University of Colorado.

Related Video: How Does NASA Spot a Near-Earth Asteroid?

Asteroids Near Venus

While scientists work on the dusty Mercury mystery, they also found that asteroids crossing the orbit of Venus may have created a similar dusty ring near Venus. Venus is the second planet out from the sun and is roughly the same size as Earth, although it has a hellish surface full of high temperatures, possibly active volcanoes, and extremely high pressure. No spacecraft has survived there for long.

Earth — which also has a dust ring, by the way — probably got its dust from the asteroid belt. That's a region between Mars and Jupiter where most space rocks in the solar system reside. As these asteroids crash into each other, they leave behind dust debris that drifts towards Earth and the inner planets. But Venus? That's a different story. Models showed that the Earth ring did not also produce a Venus ring, which leads scientists to speculate that there used to be asteroids orbiting the sun alongside Venus.

"I think the most exciting thing about this result is it suggests a new population of asteroids that probably holds clues to how the solar system formed," said co-author Marc Kuchner of NASA Goddard, in the same statement. Now the scientists are on the hunt for these asteroids.

The research, led by Petr Pokorny of the Catholic University of America and NASA Goddard, was published in the Astrophysical Journal Letters this week.

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Written by Elizabeth Howell March 15, 2019

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