Satellite in Sun Garden reveals origins of interplanetary dust

What do shooting stars and astronaut safety have in common?

Both originate from submicroscopic rock fragments found throughout the solar system, sometimes referred to as interplanetary dust.

When these particles collide with Earth’s atmosphere, they create meteors, better known as shooting stars, as the (usually) microscopic fragments vaporize and leave flaming trails in the air. When they collide with astronauts, they can punch holes in spacesuits and worse. Understanding the sources and patterns of this interplanetary dust is therefore very important for NASA, as it plans missions to the Moon, Mars and beyond.

During its revolutions around the sun, the Parker Solar Probe spacecraft, the mission that comes closest to the sun of all in space history, is bombarded by these dust particles. When they crash into the spacecraft, the tiny grains – some as small as ten thousandths of a millimeter in diameter – vaporize and release a cloud of electrically charged particles that can be detected by FIELDS, a suite of instruments. designed to detect electric and magnetic fields. .

A pair of articles published this week in The Journal of Planetary Sciences use FIELDS data to take a close look at the “zodiac cloud,” the collective term for these tiny particles.

“Every solar system has a zodiacal cloud, and we can actually explore our own and understand how it works,” said Jamey Szalay, associate researcher in astrophysical sciences at Princeton and lead author of one of the papers. “Understanding the evolution and dynamics of our zodiac cloud will allow us to better understand every zodiac observation that we have seen around any other solar system. “

The zodiac cloud diffuses sunlight in a way that can be seen with the naked eye, but only on very dark and clear nights, as moonlight or city light easily eclipses it. Thickest near the sun and thinnest near the edges of the solar system, the zodiac cloud appears smooth to the naked eye, but infrared wavelengths reveal brilliant streaks and ribbons that can be traced back to their sources: comets and asteroids.

Using data from Parker’s first six orbits, as well as computer modeling of the movement of particles in the inner solar system, Szalay and his colleagues unraveled these trails and ribbons to reveal two different populations of dust in the zodiac cloud: spiral slowly toward the sun over thousands to millions of years, known as alpha-meteoroids; then, as the swirling cloud densifies, the larger grains collide and create smaller and smaller fragments called beta-meteoroids which are then pushed back from the sun by the pressure of sunlight.

Yes, sunlight.

And not just a little pushed either. “When a fragment becomes small enough, the pressure of radiation – sunlight – is actually strong enough to force it out of the solar system,” Szalay said.

“The existence of these tiny grains has been repeatedly reported from measurements of dust from dedicated spacecraft in the region between Earth and Mars, but never in the inner solar system where these particles were thought to originate from. “said Harald Krüger, a zodiacal dust expert from the Max Planck Institute for Solar System Research and co-author of Szalay’s paper. “Thus, the FIELDS instrument offers a new window to study these dust particles entrained by sunlight near their source region.”

FIELDS also detected a narrow stream of particles that appeared to be coming from a discrete source, forming a delicate structure in the zodiacal dust cloud. To understand this third component, Szalay went back to the origins of zodiacal dust: comets and asteroids.

Comets, dust-filled snowballs traveling through our solar system in long elliptical orbits, eject large amounts of dust when they get close enough to the sun to start vaporizing their ice and dry ice. Asteroids, large and small rocks orbiting the sun between Mars and Jupiter, release dust when they collide with each other. Some of these grains are projected in any direction, but most are trapped in the orbits of their parent body, Szalay explained, which means that over thousands of orbits a comet’s track looks like more like a gravel road than an empty path with a glowing orb and a glowing trail. (Over millions of orbits, the grains will scatter beyond their orbital path, merging into the zodiacal background cloud.)

Szalay calls these dust-strewn paths “tubes” of cometary debris or asteroids. “If Earth goes through this tube anywhere, we’ll have a meteor shower,” he said.

He speculated that the Parker solar probe may have passed through one of them. “Maybe there’s a dense tube that we just couldn’t have seen other than by Parker literally flying through and getting blasted by him,” he said.

But the tubes closest to Parker’s path didn’t appear to have enough material to cause the data spike. So Szalay came up with another theory. Perhaps one of those meteoroid tubes – most likely the Geminids, which cause one of the most intense meteor showers on Earth every year – was colliding at high speed against the Inner Zodiac Cloud itself. Impacts between the tube and zodiac dust could produce large amounts of beta-meteoroids that do not take off in random directions, but focus on a narrow set of paths.

“We called this a ‘beta feed’, which is a new contribution to the field,” Szalay said. “These beta fluxes are expected to be a fundamental physical process on all circumstellar planetary disks.”

“One of the important aspects of this article is the fact that Parker Solar Probe is the first spacecraft to reach so close to the Sun that it enters regions where mutual particle collisions are most common,” said Petr Pokorný, a zodiacal cloud modeler. with NASA and the Catholic University of America, who was a co-author of Szalay’s article. “Mutual particle collisions are important not only in our solar system, but in all exosolar systems. This article gives the modeling community a unique glimpse into this hitherto unexplored territory.”

“Parker basically experienced his own meteor shower,” Szalay said. “Either it went through one of these tubes of matter or it went through a beta flow. “

The stream was also spotted by Anna Pusack, then an undergraduate student at the University of Colorado-Boulder. “I saw this wedge-shaped shape in my data, and my advisor, David Malaspina, suggested I present the work to Jamey,” she said. “The wedge shape seemed to indicate a heavy spray, or what Jamey called a beta flow in his newer designs, small particles hitting the spaceship in a very directed fashion. It was amazing for me, connecting the data that I was doing. I had analyzed theoretical work across the country, and for a young scientist, it really sparked all the excitement and possibilities that can come with working together.

Pusack is the main author of the article published in conjunction with Szalay’s. “These papers really go hand in hand,” she said. “Data supports models, and models help explain data.”

“This is a significant contribution to our understanding of the zodiac cloud, the near-sun dust environment more broadly, and the dust hazards for NASA’s Parker Solar Probe mission,” said David McComas, professor. of Astrophysical Sciences at Princeton University and Vice President. chairman of the Princeton Plasma Physics Laboratory, which is the principal investigator of ISʘIS, another instrument aboard Parker Solar Probe, and the upcoming Interstellar Mapping and Acceleration Probe (IMAP) mission.