Illustration by Photo Researchers/Getty Images

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An artist's impression of Earth surrounded by space junk.

Illustration by Photo Researchers/Getty Images

Hyperactive Sun Helping to Clear Out Space Junk

Solar activity is swelling Earth's atmosphere, causing debris to fall faster.

The recent uptick in solar flares and other activity on the sun could one day cripple satellites or knock out power grids on Earth. But in the meantime, the solar maelstrom has been helping to clear out space junk, NASA scientists report.

Right now some tens of millions of pieces of space junk are circling our planet—broken satellites, rocket parts, and other human-made materials trapped in orbit. That includes pieces from a Chinese probe that was destroyed during an anti-satellite missile test in 2007.

In the latest issue of NASA's Orbital Debris Quarterly News, agency scientist Nicholas Johnson notes that an increased influx of solar heat is causing Earth's upper atmosphere—specifically, a layer known as the thermosphere—to swell.

In turn, the puffed-up thermosphere has accelerated the rate at which the Chinese satellite debris is being removed from Earth's orbit, Johnson found. (Also see "NASA Satellite Falling Faster Due to Solar Activity.")

In general, "the increase in solar activity causes more energy to be deposited into the atmosphere, which in turn is heated and expands," explained Johnson, chief scientist of NASA's Orbital Debris Program Office at the Johnson Space Center in Houston.

"This increases atmospheric density at a given altitude, thereby increasing drag. This causes [orbiting space junk] to lose energy and fall into a lower orbit," where the debris eventually reenters the atmosphere, Johnson said in an email.

Space Junk Flushed Like Leaves From Gutters

In 2007 China deliberately destroyed its Fengyun-1C weather satellite to test anti-satellite technology. (Related photos: "Satellite Collision Creates Dangerous Debris.")

NASA estimates that about 6 percent of the 3,218 cataloged pieces of debris from Fengyun-1C have since reentered Earth's atmosphere.

Half of those objects were destroyed during the past year alone, which coincides neatly with a ramp up in the sun's activity as it enters the next anticipated solar maximum—when solar activity is at its peak—in 2013.

In total, more than a hundred metric tons of space junk have been destroyed in the past year. The majority of this debris would have reentered the atmosphere sooner or later—increased solar activity simply sped up the process, Johnson said.

"The more susceptible objects will fall out first, similar to flushing leaves from your house gutters," he said.

While most of the objects that fall from they sky are vaporized before they hit the ground, some pieces are large enough that they could survive reentry and pose threats.

"Last year," Johnson said, "there were 17 spacecraft and 8 rocket bodies which reentered in an uncontrolled manner, including two spacecraft and one rocket body from the 1960s."

Johnson predicts that the sun's effect on the thermosphere will last through next year's solar max, but that the atmospheric swelling—and thus the space-junk purge—will begin to decrease soon after that.