Just as dust accumulates in the corners and along the shelves of our homes, dust also accumulates in space. But when dust settles in the solar system, it is often in rings. Several rings of dust surround the Sun. The rings trace the orbits of the planets, whose gravity drags the dust into place around the Sun, as it moves towards the center of the solar system.
The dust consists of remains crushed by the formation of the solar system, about 4.6 billion years ago: rubble from collisions of asteroids or crumbs of burning comets. The dust is dispersed throughout the solar system, but is collected in grainy rings that overlook the orbits of the Earth and Venus, rings that can be seen with telescopes on Earth. By studying this dust ̵
Two recent studies report new discoveries of dust rings in the inner solar system. A study uses NASA data to delineate evidence of a dust ring around the Sun at Mercury's orbit. A second NASA study identifies the probable source of dust ring in the orbit of Venus: a group of asteroids never previously detected in co-orbit with the planet.
"It is not every day that we discover something new in the inner solar system," said Marc Kuchner, author of the study of Venus and astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "This is right in our neighborhood."
In this illustration, several dust rings surround the Sun. These rings are formed when the gravity of the planets drags the dust grains into orbit around the Sun. Recently, scientists have detected an orbit ring of dust of Mercury. Others speculate that the source of the Venus dust ring is a group of co-orbital asteroids never previously identified.
( NASA Goddard Space Flight Center / Mary Pat Hrybyk-Keith)
Another ring around the Sun
Guillermo Stenborg and Russell Howard, both solar scientists at the Naval Research Laboratory in Washington, D.C., have not decided to find a dust ring. "We found it by accident," Stenborg said, laughing. The scientists summarized their findings in an article published in The Astrophysical Journal on November 21, 2018.
Describe evidence of a subtle cosmic dust haze on the Mercury orbit, forming a ring about 9.3 million wide of miles. Mercury – 3,030 miles wide, barely large enough to allow the continental United States to lengthen – wading through this vast track of dust as it encircles the Sun.
Ironically, the two scientists stumbled into the dust ring as they searched the proofs of a dust -the free region near the sun At a certain distance from the Sun, according to a decades-old prediction, the powerful heat of the star should vaporize the dust, sweeping an entire space. Knowing where this border is located can reveal to scientists the composition of the dust itself and suggest how planets are formed in the young solar system.
So far no evidence of dust-free space has been found, but this is due in part it would be difficult to detect from the Earth. Regardless of how scientists look from the Earth, all the dust between us and the Sun intrudes, causing them to think that perhaps the space near the Sun is dusty more than it really is.
Stenborg and Howard thought they could work around this problem by building a model based on images of interplanetary space from NASA's STEREO satellite – short for the Observatory of Solar and Terrestrial Relations.
Scientists think the planets begin as mere grains of dust. They emerge from the gigantic discs of gas and dust that surround the young stars. Gravity and other forces cause the material inside the disc to collide and coalesce.
( NASA Jet Propulsion Laboratory
Ultimately, the two wanted to test their new model in preparation for NASA's Parker solar probe, which is currently flying a highly elliptical orbit around the Sun , oscillating ever closer to the star over the next seven years. They wanted to apply their technique to the images that Parker will send to Earth and see how the dust behaves near the Sun.
Scientists have never worked with the data collected in this unexplored territory, so close to the Sun. Models such as Stenborg and Howard provide a crucial context for understanding the observations of Parker Solar Probe, as well as suggesting what kind of space environment the spaceship will be in: sooty or sparkling.
Two types of light appear in the STEREO images: the light coming from the fascinating external atmosphere of the Sun – called the crown – and the light rifles knows from all the dust floating in space. The sunlight reflected from this dust, which slowly orbits around the Sun, is about 100 times brighter than coronal light.
"We are not really people of dust," said Howard, who is also the principal scientist for cameras on STEREO and Parker Solar Probe taking pictures of the crown. "The dust near the Sun shows itself in our observations and, in general, we threw it away." Solar scientists like Howard – who study solar activity for purposes such as the prediction of an impending spatial time, including gigantic explosions of solar material that the Sun can sometimes send on our way – have spent years developing techniques to remove solar energy. Effect of this powder. Only after removing the slight contamination from the dust can they clearly see what the crown is doing.
The two scientists built their model as a tool to get rid of the annoying dust in STEREO – and eventually Parker Solar Probe – images, but the dust-free space forecast lingered in their minds. If they could devise a way to separate the two types of light and isolate the splendor of the dust, they could understand how much dust was really there. Finding that all the light in an image came from the crown alone, for example, could indicate that they had finally found a dust-free space.
Mercury's dust ring was a fortunate discovery, a lateral 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 the Mercury orbit – more dust, that is – in the light they would otherwise have scheduled to discard.
"It wasn't an isolated thing," Howard said. "All around the Sun, regardless of the position of the spaceship, we could see the same 5% increase in brightness or density of the dust." Having said that it was something, and it is something that extends all around the Sun. "
Scientists have never considered that a ring could exist along the orbit of Mercury, which is perhaps why it has not been detected until now, Stenborg said. "People thought that Mercury, unlike Earth or Venus, was too small and too close to the Sun to capture a dust ring," he said. "They expected that the solar wind and the magnetic forces of the Sun would wipe out any excess dust from the Mercury orbit."
With an unexpected discovery and a new sensitive instrument in their scope, the researchers are still interested in the dust-free area. While Parker Solar Probe continues its exploration of the crown, their model can help others reveal other dust bunnies lurking near the Sun.
Asteroids hide in the orbit of Venus
This is not the first time that scientists have found a ring of dust in the inner solar system. Twenty-five years ago, scientists discovered that the Earth orbits around the Sun within a giant ring of dust. Others have discovered a similar ring near the orbit of Venus, first using archive data from German-American Helios space probes in 2007, and confirming it in 2013, with STEREO data.
Since then, scientists have determined the dust ring in Earth's orbit comes largely from the asteroid belt, the vast donut-shaped region between Mars and Jupiter, where most of the asteroids of the solar system. These rocky asteroids constantly clash with one another, causing the dust that penetrates deeper into the gravity of the Sun to slide, unless the Earth's gravity pulls the dust into our orbit. planet.
In the beginning it seemed probable that the Venus dust ring formed like the Earth, from dust produced elsewhere in the solar system. But when Goddard's astrophysicist Petr Pokorny modeled the powder that spiraled toward the Sun from the asteroid belt, his simulations produced a ring that corresponded to the observations of the Earth's ring – but not of Venus.
This discrepancy made him ask if not the band of asteroids, where else does the dust come from in the orbit of Venus? After a series of simulations, Pokorny and his research partner Marc Kuchner hypothesized that it comes from a group of asteroids never detected that orbit the Sun together with Venus. They published their work on The Astrophysical Journal Letters on 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 how the solar system was formed", Kuchner said. . If Pokorny and Kuchner can observe them, this family of asteroids could shed light on Earth and the early stories of Venus. Seen with the right tools, asteroids could also reveal clues to the chemical diversity of the solar system.
Because it is dispersed on a larger orbit, the Venus dust ring is much larger than the one just detected at Mercury. About 16 million miles from top to bottom and 6 million miles wide, the ring is littered with dust whose larger grains are roughly the size of those in coarse sandpaper. It is about 10 percent more dense than dust in the surrounding space. However, it's widespread: put all the dust in the ring together and all you get is a two-mile asteroid.
Using a dozen different modeling tools to simulate the way the 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 has tried seems a reminder of all the rocky objects of the solar system: asteroids of the Main Belt, comets of Oort Cloud, comets of the Halley type, comets of the family of Jupiter, recent collisions in the band asteroids.  "But none of them worked," Kuchner said. "So, we started inventing our dust sources."
Perhaps, the two scientists thought, the dust came from asteroids much closer to Venus than the asteroid belt. There may be a group of asteroids in orbit around the Sun with Venus – meaning that they share the orbit of Venus, but they are far from the planet, often from the other side of the Sun. Pokorny and Kuchner have reasoned a group of asteroids in the orbit of Venus that could have gone unnoticed until now because it is difficult to point the terrestrial telescopes in that direction, so close to the Sun, without luminous interference from the Sun.
Asteroids represent constituent elements of the rocky planets of the solar system. When they collide in the asteroid belt, they scatter scattering dust into the solar system, which scientists can study to find clues to the history of the planets.
( Conceptual image laboratory of NASA's Goddard Space Flight Center
Co-orbiting asteroids are an example of what is called a resonance, an orbital model that blocks different orbits, depending on how their gravitational influences meet, Pokorny and Kuchner have modeled many potential resonances: asteroids surrounding the Sun twice for every three Venus orbits, for example, or nine times for ten of Venus, and one by one. , only one group produced a realistic simulation of the dust ring of Venus: a pack of asteroids that occupies the orbit of Venus, combining the travels of Venus around the Sun one by one.
But the scientists could not simply call a day after finding a hypothetical solution that worked. "We thought we had discovered this asteroid population, but then we had to prove it and show it works. "said Pokorny. "We got excited, but then you realize, & # 39; Oh, c & # 39; it's so much work to do. & # 39;"
They needed to prove that the very existence of asteroids makes sense in the solar system. It would be unlikely, they realized, that the asteroids in these special circular orbits near Venus came from somewhere else like the asteroid belt. Their hypothesis would make more sense if the asteroids had been there since the beginning of the solar system.
Scientists have built another model, this time from a crowd of 10,000 asteroids near Venus. They advanced the simulation forward for 4.5 billion years of solar system history, incorporating all the gravitational effects of each of the planets. When the model reached the current day, about 800 of their tested asteroids survived the test of time.
Pokorny considers this an optimistic survival rate. It indicates that the asteroids would have formed near the orbit of Venus in the chaos of the first solar system, and some could remain there today, feeding the dust ring nearby.
The next step is actually pinning 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 telescopes such as Hubble, or perhaps interplanetary space imagers similar to those of STEREO. So, scientists will have more questions to answer: how many of them are there and how big are they? Continuously spreading dust, or was it a single breaking event?
Dust sounds around other stars
In this illustration, an asteroid disintegrates under the powerful gravity of LSPM J0207 + 3331, a white dwarf star located about 145 light-years away. Scientists believe that crumbling asteroids provide the dust rings that surround this old star.
NASA's Goddard Space Flight Center / Scott Wiessinger)
The dust sounds that Mercury and Venus are just a planet or two away, but scientists have identified many other dust rings in distant star systems. Vast rings of dust can be easier to spot than exoplanets and could be used to deduce the existence of otherwise hidden planets and even their orbital properties.
But interpreting extrasolar dust rings is not simple. "To model and accurately read dust rings around other stars, we must first understand the physics of dust in our backyard," Kuchner said. By studying dust rings close to Mercury, Venus and Earth, where dust traces the lasting effects of gravity in the solar system, scientists can develop techniques for reading between dust rings both near and far.
This article originally appeared on NASA. Follow @ NASA on Twitter.
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