What scientists discovered after filtering dust in the solar system

The dust consists of crushed remains of the formation of the solar system, about 4.6 billion years ago – debris due to collisions of asteroids or crumbs of comets in flames. The dust is scattered throughout the solar system, but it accumulates at the level of the granular rings covering the orbits of the Earth and Venus, rings visible with the help of telescopes on Earth. By studying this dust – what it's made of, where it comes from and how it moves in space – scientists are looking for clues to understand the birth of planets and the composition of everything we see in 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 the orbit of Venus: a group of asteroids never detected co-orbiting the planet.

"It's not every day that we discover something new in the inner solar system," said Marc Kuchner, author of the Venus and Astrophysicist study at the Goddard Space Flight Center. NASA in Greenbelt, Maryland. "It's just in our neighborhood."

Another ring around the sun

Guillermo Stenborg and Russell Howard, both scientists specializing in the field of solar energy at the Naval Research Laboratory in Washington, have decided not to find a ring of dust. "We found it by chance," Stenborg said, laughing. Scientists have summarized their findings in an article published in The astrophysical journal November 21, 2018.

They describe the evidence of a thin cloud of cosmic dust on the orbit of Mercury, forming a ring of about 9.5 million kilometers wide. Mercury – 3030 miles wide, just big enough for the mainland of the United States to extend – crosses this vast dust trail that bypasses the Sun.

Ironically, both scientists came across the ring of dust while they were looking for evidence of a dust-free region close to the Sun. According to a prediction made several decades ago, at a certain distance from the Sun, the powerful heat of the star should vaporize the dust, thus sweeping all the space. Knowing where this limit is can help educate scientists about the composition of the dust itself and how the planets formed in the young solar system.

Until now, no evidence of dust-free space has been found, but that's partly because it would be hard to detect from the Earth. Regardless of the scientists' eyes from Earth, all the dust between us and the Sun is bothering us, which makes them think that the space near the Sun is more dusty than it is. is really.

Stenborg and Howard thought they could work around this problem by building a model based on interplanetary space images from NASA's STEREO satellite (an abbreviation for observing solar and terrestrial relationships).

In the end, they wanted to test their new model in anticipation of NASA's Solar Parker solar probe, which is currently spinning in a highly elliptical orbit around the Sun, getting closer to the star over the course of next seven years. They wanted to apply their technique to the images that Parker will send to Earth and observe the behavior of dust near the Sun.

Scientists have never worked with data collected in this unexplored territory, so close to the sun. Models such as Stenborg and Howard provide a crucial context for understanding the Parker Solar Probe observations, as well as for indicating the type of spatial environment in which the spacecraft will be: cleanliness or cleanliness.

Two types of light appear in STEREO images: the light of the flaming outer atmosphere of the Sun, called the corona, and the light reflected by all the dust floating in the space. The sunlight reflected by this dust, which rotates slowly around the Sun, is about 100 times brighter than the coronal lumen.

"We are not really dusty people," said Howard, who is also the lead scientist of STEREO and Parker Solar Probe cameras, taking pictures of the wreath. "The dust near the sun just appears in our sightings, and usually we throw it." Scientists from the solar energy sector such as Howard, who are studying solar activity for such purposes as the prediction of imminent space weather, including giant explosions of solar material that the Sun can sometimes show us. send, have spent years developing techniques to eliminate the effect of this dust. It is only after eliminating the slight contamination of the dust that they can clearly see what the crown does.

Both scientists have designed their model as a tool allowing others to get rid of the cumbersome dust of STEREO images – and possibly Parker Solar Probe – but the prediction of a dust-free space always resided in their minds. If they could find a way to separate the two types of light and isolate the dust, they could determine the amount of dust actually present. Finding that all the light in an image came from the crown alone, for example, might indicate that they had finally found a dust-free space.

The Mercury Dust Ring was a find, a secondary discovery that Stenborg and Howard made while they were working on their model. When they used their new technique on STEREO images, they noticed an improved brightness pattern along Mercury's orbit – more dust, that is, at the light that they had otherwise planned to delete.

"It was not an isolated thing," Howard said. "All around the Sun, regardless of the position of the spacecraft, we could see the same 5% increase in brightness or density of dust." That said, there was something there and it's something that extends all around the Sun. "

Scientists have never envisioned the existence of a ring along the orbit of Mercury, which may explain why it was not detected until it reached the end of the day. now, said Stenborg. "People thought that Mercury, unlike Earth or Venus, is too small and too close to the Sun to capture a ring of dust," he said. "They expected the solar wind and the magnetic forces of the Sun to chase excess dust out of Mercury's orbit."

With an unexpected discovery and a new tool sensitive to their assets, researchers are still interested in the dust-free zone. While Parker Solar Probe continues its exploration of the crown, their model can help others reveal the presence of other dusty rabbits hidden near the Sun.

Asteroids hidden in the orbit of Venus

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 ring of dust in Earth orbit came largely from the asteroid belt, the vast donut-shaped region located between Mars and Jupiter, where most asteroids live. of the solar system. These rocky asteroids clash against each other, releasing dust deeper into the gravity of the Sun, unless the gravity of the Earth clears the dust in the orbit of our planet.

At first, it seemed likely that the Venus dust ring was forming like that of the Earth, from 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 matched the observations of the Earth's ring, but not to those of Venus.

This gap made him wonder if it was not the asteroid belt, where would the dust come from in the orbit of Venus? 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 letters of the astrophysical journal March 12, 2019.

"I think the most exciting thing about this result is that it suggests a new population of asteroids that probably contains clues about the formation of the solar system," said Kuchner. 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 scattered in a larger orbit, the Venus dust ring is much larger than the ring recently 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. Yet it is 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. A group of asteroids could co-orbit the Sun with Venus, which means that 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 in orbit of Venus might not have been detected until now, as it is difficult to point terrestrial telescopes in this direction, so close to the Sun. , without light interference from the Sun.

The co-orbiting asteroids are an example of what is called a 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, only one group produced a realistic simulation of the Venus dust ring: a group of asteroids occupying the orbit of Venus, corresponding to the journeys of Venus around the Sun one by a.

But scientists could not call it a 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 could be formed near the orbit of Venus in the chaos of the early solar system, and that some might stay there today, thus feeding the dust ring. located nearby.

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?

Dust rings around other stars

The rings of dust that Mercury and Venus Shepherd are only a planet or two away, but scientists have spotted many other dust rings in distant star systems. The vast rings of dust may be easier to spot than exoplanets and could be used to infer the existence of otherwise hidden planets and even their orbital properties.

But interpreting the extrasolar dust rings is not simple. "In order to model and accurately read the dust rings around other stars, we must first understand the physics of dust in our own garden," said Kuchner. By studying the neighboring dust rings of Mercury, Venus and the Earth, where dust traces the lingering effects of gravity in the solar system, scientists can develop reading techniques between near and far dust rings.

Explore further:
Ring of suspected dust on the orbit of Venus confirmed

More information:
Petr Pokorný et al, The co-orbital asteroids as source of the zodiacal dust ring of Venus, The astrophysical journal (2019). DOI: 10.3847 / 2041-8213 / ab0827