Posted on March 13, 2019
"It's not every day that we discover something new in the internal solar system," said Marc Kuchner, author of a study on Venus and astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, in Maryland. "This is right in our neighborhood. I think the most exciting thing about this result is that it suggests a new population of asteroids that would probably hold clues to the formation of the solar system. "
Two recent studies report new discoveries of dust rings in the internal solar system. A study uses NASA data to describe evidence of a ring of dust around the Sun in Mercury's orbit. A second NASA study identifies the probable source of the ring of dust on Venus' orbit: a group of asteroids never detected co-orbiting the planet.
This is not the first time scientists have discovered a ring of dust in the internal solar system. Twenty-five years ago, scientists discovered that the Earth gravitated around the Sun in a gigantic ring of dust. Others have discovered a similar ring near the orbit of Venus, first using the US-German space probe data from Helios in 2007, then confirming in 2013 with the data. STEREO.
Since then, scientists have determined that the dust ring in Earth orbit came largely from the asteroid belt, the vast donut-shaped region between Mars and Jupiter, where most of the asteroids in the solar system live. These rocky asteroids clash against each other, releasing dust deeper into the Sun's gravity, unless Earth's gravity deflects it into its orbit.
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At first, it seemed likely that the Venus dust ring formed like the Earth, from the dust produced elsewhere in the solar system. But when astrophysicist Goddard Petr Pokorny modeled the spiral dust toward the Sun from the asteroid belt, his simulations produced a ring that matches the observations of the Earth's ring – but not that of Venus.
This gap made him wonder if it was not the asteroid belt, where did the dust come from Venus' orbit? After a series of simulations, Pokorny and his research partner Marc Kuchner hypothesized that it came from a group of never-detected asteroids that revolve around the Sun alongside Venus. They published their work in The Astrophysical Journal Letters on March 12, 2019.
If Pokorny and Kuchner can observe them, this family of asteroids could illuminate the first story of Earth and Venus. Viewed with the right tools, asteroids could also reveal clues about the chemical diversity of the solar system.
As it is dispersed in a larger orbit, the Venus dust ring is much larger than the one just detected at Mercury. About 16 million kilometers from top to bottom and 6 million kilometers wide, the ring is covered with dust whose larger grains are about the size of those of a coarse sand paper. It is about 10% more dense in dust than the surrounding area. That said, it's diffuse: collect all the dust from the ring and get a two-mile asteroid.
Using a dozen different modeling tools to simulate the evolution of dust in the solar system, Pokorny modeled all sources of dust he could think of, looking for a simulated ring of Venus that matches the observations. The list of all the sources that he has tried sounds like a call from all the rocky objects of the solar system: Main Belt asteroids, Oort Cloud comets, Halley-type comets, Jupiter family comets, recent collisions in the belt d & # 39; asteroids.
"But none of them worked," said Kuchner. "So we started to create our own sources of dust."
Perhaps, the two scientists thought, the dust came from asteroids much closer to Venus than the asteroid belt. It is possible that a group of asteroids co-orbit the Sun with Venus, which means they share the orbit of Venus, but stay away from the planet, often on the other side of the Sun. Pokorny and Kuchner felt that a group of asteroids on the orbit of Venus could have been detected until now, as it is difficult to point terrestrial telescopes in this direction, so close of the Sun, without light interference from the Sun.
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Co-orbiting asteroids are an example of what is called resonance, an orbital pattern that locks different orbits together, depending on how their gravitational influences meet. Pokorny and Kuchner have modeled many potential resonances: asteroids that surround the Sun twice for three orbits of Venus, for example, or nine times for the ten of Venus and one for one. Of all the possibilities, one group produced on its own a realistic simulation of the Venus dust ring: a group of asteroids occupying the orbit of Venus, corresponding to the movements of Venus around the Sun one by one.
But scientists could not call each other one day after finding a hypothetical solution that worked. "We thought we had discovered this population of asteroids, but then we had to prove it and show that it worked," said Pokorny. "We're excited, but then you realize," Oh, there's so much work to do. "
They had to show that the very existence of asteroids made sense in the solar system. They were probably aware that the asteroids of these special circular orbits located near Venus had arrived elsewhere, such as the asteroid belt. Their hypothesis would make more sense if the asteroids were there from the very beginning of the solar system.
Scientists built another model, starting this time with a crowd of 10,000 neighboring asteroids from Venus. They allow the simulation to accelerate its 4.5 billion years of history of the solar system, integrating all the gravitational effects of each of the planets. When the model reached the current stage, about 800 of their asteroids tested have survived the test of time.
Pokorny sees this as an optimistic survival rate. This indicates that asteroids may have formed near the orbit of Venus in the chaos of the early solar system, and that some may remain there today, thus fueling the nearby ring of dust.
The next step is to identify and observe the elusive asteroids. "If there is something out there, we should be able to find it," Pokorny said. Their existence could be verified with space telescopes like Hubble, or perhaps interplanetary space imagers similar to those of STEREO. Scientists will then have other questions to answer: how many are there and how big are they? Do they continually lose dust or have there been only one dissolution event?
Image credit: Moon, Venus, Jupiter, Earth of the ISS
The Daily Galaxy via NASA / Goddard Space Flight Center