Swarm of Asteroids Orbiting the Sun?

 

Moon, Jupiter, Venus, Earth from the ISS

 

“This group of asteroids we hypothesized is probably about 1000-times less well populated than the asteroid belt,” NASA astrophysicist Marc Kuchner at the Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, told The Daily Galaxy about a group of 10,000 asteroids discovered co-orbiting the Sun with Venus. “We don’t know if they were all produced in one big break-up event. But if this group is like the main asteroid belt, there probably were some recent breakups in the last few million years that have left their imprint on the dust cloud. By the way…some of these objects will probably work their way into orbits that cross the Earth’s orbit, and become near-Earth asteroids.”

Clues to how the solar system formed

“It’s not every day you get to discover something new in the inner solar system,” said Kuchner.”This is right in our neighborhood. 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.”

Two 2019 studies reported discoveries of dust rings in the inner solar system. One study used NASA data to outline evidence for a dust ring around the Sun at Mercury’s orbit. A second study from NASA identifies the likely source of the dust ring at Venus’ orbit: a group of a few hundred asteroids co-orbiting with the planet.

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This isn’t the first time scientists have found a dust ring in the inner solar system. Twenty-five years ago, scientists discovered that Earth orbits the Sun within a giant ring of dust. Others uncovered a similar ring near Venus’ orbit, first using archival data from the German-American Helios space probes in 2007, and then confirming it in 2013, with STEREO data. Launched in October 2006, the Solar Terrestrial Relations Observatory, or STEREO, has provided scientists a unique and revolutionary view of the Sun-Earth System.

Since then, scientists determined the dust ring in Earth’s orbit comes largely from the asteroid belt, the vast, doughnut-shaped region between Mars and Jupiter where most of the solar system’s asteroids live. These rocky asteroids constantly crash against each other, sloughing dust that drifts deeper into the Sun’s gravity, unless Earth’s gravity pulls the dust aside, into our planet’s orbit.

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Matched Earth’s Ring, Not Venus’

At first, it seemed likely that Venus’ dust ring formed like Earth’s, from dust produced elsewhere in the solar system. But when Goddard astrophysicist Petr Pokorny modeled dust spiraling toward the Sun from the asteroid belt, his simulations produced a ring that matched observations of Earth’s ring — but not Venus’.

 

Points to a Group of Never-Before-Detected Asteroids 

This discrepancy made Pokorny wonder if not from the asteroid belt, where else does the dust in Venus’ orbit come from? After a series of simulations, Pokorny and his research partner Kuchner hypothesized it comes from a group of never-before-detected asteroids that orbit the Sun alongside Venus. 

If Pokorny and Kuchner can observe them, this family of asteroids could shed light on Earth and Venus’ early histories. Viewed with the right tools, the asteroids could also unlock clues to the chemical diversity of the solar system.

Because it’s dispersed over a larger orbit, Venus’ dust ring is much larger than the newly detected ring at Mercury’s. About 16 million miles from top to bottom and 6 million miles wide, the ring is littered with dust whose largest grains are roughly the size of those in coarse sandpaper. It’s about 10 percent denser with dust than surrounding space. Still, it’s diffuse — pack all the dust in the ring together, and all you’d get is an asteroid two miles across.

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The Source?

Using a dozen different modeling tools to simulate how dust moves around the solar system, Pokorny modeled all the dust sources he could think of, looking for a simulated Venus ring that matched the observations. The list of all the sources he tried sounds like a roll call of all the rocky objects in the solar system: Main Belt asteroids, Oort Cloud comets, Halley-type comets, Jupiter-family comets, recent collisions in the asteroid belt.

“But none of them worked,” Kuchner said. “So, we started making up our own sources of dust.”

Undetected in Venus’s Orbit

Perhaps, the two scientists thought, the dust came from asteroids much closer to Venus than the asteroid belt. There could be a group of asteroids co-orbiting the Sun with Venus — meaning they share Venus’ orbit, but stay far away from the planet, often on the other side of the Sun. Pokorny and Kuchner reasoned a group of asteroids in Venus’ orbit could have gone undetected until now because it’s difficult to point earthbound telescopes in that direction, so close to the Sun, without light interference from the Sun.

A “Resonance”

Co-orbiting asteroids are an example of what’s called a resonance, an orbital pattern that locks different orbits together, depending on how their gravitational influences meet. Pokorny and Kuchner modeled many potential resonances: asteroids that circle the Sun twice for every three of Venus’ orbits, for example, or nine times for Venus’ ten, and one for one. Of all the possibilities, one group alone produced a realistic simulation of the Venus dust ring: a pack of asteroids that occupies Venus’s orbit, matching Venus’ trips around the Sun one for one.

“We thought we’d discovered this population of asteroids, but then had to prove it and show it works,” Pokorny said. “We got excited, but then you realize, ‘Oh, there’s so much work to do.'”

They needed to show that the very existence of the asteroids makes sense in the solar system. It would be unlikely, they realized, that asteroids in these special, circular orbits near Venus arrived there from somewhere else like the asteroid belt. Their hypothesis would make more sense if the asteroids had been there since the very beginning of the solar system.

The scientists built another model, this time starting with a throng of 10,000 asteroids neighboring Venus. They let the simulation fast forward through 4.5 billion years of solar system history, incorporating all the gravitational effects from each of the planets. When the model reached present-day, about 800 of their test asteroids survived the test of time.

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Formed Near Venus in the Chaos of the Early Solar System

Pokorny considers this an optimistic survival rate. It indicates that asteroids could have formed near Venus’ orbit in the chaos of the early solar system, and some could remain there today, feeding the dust ring nearby.

The next step is actually pinning down and observing the elusive asteroids. “If there’s something there, we should be able to find it,” Pokorny said. Their existence could be verified with space-based telescopes like Hubble, or perhaps interplanetary space-imagers similar to STEREO’s. Then, the scientists will have more questions to answer: How many of them are there, and how big are they? Are they continuously shedding dust, or was there just one break-up event?

Image credit: Moon, Venus, Jupiter, Earth from the ISS

Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona via Marc Kushner and NASA/Goddard Space Flight Center

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