THE WOODLANDS, Texas — Grains of dust from the edge of the solar system could be finding their way to Earth. And NASA may already have a handful of the debris, researchers report.
With an estimated 40,000 tons of space dust settling in Earths stratosphere every year, the U.S. space agency has been flying balloon and aircraft missions since the 1970s to collect samples. The particles, which can be just a few tens of micrometers wide, have long been thought to come mostly from comets and asteroids closer to the sun than Jupiter (SN Online: 3/19/19).
But it turns out that some of the particles may have come from the Kuiper Belt, a distant region of icy objects orbiting beyond Neptune, NASA planetary scientist Lindsay Keller said March 21 at the Lunar and Planetary Science Conference. Studying those particles could reveal what distant, mysterious objects in the Kuiper Belt are made of, and perhaps how they formed (SN Online: 3/18/19).
“Were not going to get a mission out to a Kuiper Belt object to actually collect [dust] samples anytime soon,” Keller said. “But we have samples of these things in the stratospheric dust collections here at NASA.”
One way to find a dust grains home is to probe the particle for microscopic tracks where heavy charged particles from solar flares punched through. The more tracks a grain has, the longer it has wandered in space — and the more likely it originated far from Earth, says Keller, who works at the Johnson Space Center in Houston.
But to determine precisely how long a dust grain has spent traveling space, Keller first needed to know how many tracks a grain typically picks up per year. Measuring that rate required a sample with a known age and known track density — criteria met only by moon rocks brought back on the Apollo missions. But the last track-rate estimate was done in 1975 and with less precise instruments than are available today.
So Keller and planetary scientist George Flynn of SUNY Plattsburgh reexamined that same Apollo rock with a modern electron microscope. They found that the rate at which rocks pick up flare tracks was two orders of magnitude lower than the previous study estimated.
That means it takes longer for dust flakes to pick up tracks than astronomers assumed. When Keller and Flynn counted the number of tracks in 14 atmospheric dust grains, the pair found that some of the particles must have spent millions of years out in space — far too long to have come just from between Mars and Jupiter.
Grains specifically from the Kuiper Belt would have wandered 10 million years to reach Earths stratosphere, the researchers calculated. Thats “pretty solid evidence that were collecting Kuiper Belt dust right here,” Keller says.
Four of the particles contained minerals that had to have formed through interactions with liqRead More – Source
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