Earth-bound space dust comes from the edge of the solar system
When you notice that faint glow of reflected sunlight in the dark sky just before dawn and after dusk, you are actually looking at the zodiacal dust cloud. Dust shrouds our inner solar system, and up to 30,000 tons of its particles drift through Earth’s atmosphere every year, according to some estimates.
This dust has long been thought to come from collisions in the main asteroid belt as well as among Jupiter-family comets – with particles unlikely to reach Earth from the Kuiper Belt, a doughnut-shaped region in the beyond the orbit of Neptune which contains comets, asteroids and other icy objects. In a recent study Posted in natural astronomyhowever, researchers have discovered zodiac cloud dust particles from the far reaches of our solar system.
on the wrong path
Lindsay Keller, planetary scientist at NASA’s Johnson Space Center and lead author of the study, first discovered the evidence when he examined a sample of moon rock brought to Earth by the Apollo 16 astronauts. Using a diamond knife, Keller cut and shaved a slice about a thousand times thinner than a human hair and visualized it using a transmission electron microscope.
Specifically, Keller researched the damage caused by energetic particles from the Sun: “These high-energy ions disrupt the crystal structure of minerals and leave behind ‘traces,'” he says, adding that the traces look like cures. – teeth fallen on the ground. Using the density of these tracks and an estimate of the number of tracks that form each year, researchers can determine how long a rock has been in space.
To his surprise, however, Keller discovered that the true rate of lead production is much lower than previously estimated. “That’s when the alarm bells started ringing,” he says. The researchers had determined the original rate by using chemicals to etch traces on a thicker sample of the same moon rock. But examination of this finer sample under a microscope revealed fewer traces per unit area – and, therefore, a lower production rate.
“There’s nothing wrong with the etching technique and the corresponding production rate,” says Keller. “You just have to be careful to use the rate that suits your technique.”
A difficult journey
Working with George Flynn, an astrophysicist at the State University of New York at Plattsburgh, Keller selected a sample of dust grains that had previously entered Earth’s atmosphere and been collected by NASA high-altitude aircraft. . Using their new production rate, the researchers found that some of the grains must have spent more than a million years heading towards Earth.
“The surprise was how many there were,” Flynn says. “Using the correct calibration showed that many more particles had trajectory densities that imply they came from afar – not the main-belt asteroid or Jupiter-family comet origin which doesn’t take than tens of thousands of years to reach Earth.”
However, to spiral from Neptune, the dust grains would have to pass through the gravity of the gas giants, where their orbits could become trapped or even ejected from the solar system. So the researchers turned to a variety of computer models that simulated the changing orbits of dust grains.
“Depending on the model you use, a fraction of the particles may pass through,” Keller explains. While there’s also a greater chance that particles will be destroyed by collisions with interstellar grains — especially over millions of years — even a small fraction results in many dust grains reaching Earth, Flynn says. . “There is a huge amount of dust produced in the Kuiper Belt.”
Researchers estimate that a quarter of all the dust that makes up the zodiacal cloud comes from the Kuiper Belt. Particles arriving on Earth likely have low velocities, allowing grains to survive entry into Earth’s atmosphere without burning. “For the first time,” Flynn explains, “we can look at track densities and know where these particles are coming from.”