We have a space junk problem. Fragments from very small (a millimeter) to much bigger (several meters) are whirling around overhead at fantastic speeds, threatening satellites and astronauts. Adding more could actually help us out. Wouldn't you know that tons of tungsten metal dust could help us out here.
Many proposals have been suggested to tackle space junk, but lots of them are too tricky, too expensive or operate only on future rocket launches or larger pieces of hardware. Except for a new idea dreamed up in the U.S. Naval Research Laboratory, which is so pedestrian in its simplicity that it's instantly appealing.
Space junk is a problem, have no doubt about it. If it sounds too exotic a matter for you to worry about, remember that the International Space Station—a giant metal and ceramic and glass structure that dwarfs a football field—needs to be shifted in its orbit from time to time to avoid a whirling piece of dead satellite, a dropped astronaut tool, or another unidentified bit of debris. Otherwise the junk might fly through the ISS's fragile, pressurized living space at several times the speed of sound. And that's not good. A single fleck of paint, broken off a long-dead rocket but still in orbit, can seriously batter the Space Shuttle's windows. As we put more hardware into space—and rely on it more—so the issue of space junk gets ever more serious.
Gurudas Ganguli and his colleagues have speculated that by hauling tons upon tons of tungsten dust up into orbit, and then distributing it into a thin cloud that would eventually form a diffuse ring around the Earth—like a mini Saturn—the dust will act to slowly clear the orbit of debris that measures up to 10 centimeters (almost four inches). This could actually be the most dangerous size of debris because it's too small to be tracked, and there are tens of thousands of bits this size out there (much more now after the Chinese destroyed a satellite in orbit, and after a catastrophic collision between satellites).
Ganguli's theory is simple: The tungsten would adhere to space junk it encountered, and over time the junk would accumulate a coating of tungsten dust that would eventually change its orbit. At a critical juncture the now-coated junk's orbit would tighten to the point it begins to brush the outer atmosphere, and then aerobraking would rob it of enough of its speed that it would then burn up—taking it, and its dusty tungsten jacket with it, safely out of orbit.
There are a number of flaws with the idea—starting with how best to safely distribute it the tons of dust. And the dust itself could be considered space junk, especially if it accumulates by itself into little balls. De-orbiting debris would move through satellite orbits in unpredictable ways, potentially jeopardizing their safety. And so on. But the idea does have merit thanks to its relatively low cost, and the fact that unlike some theories about deploying solar balloons or sails on debris, flying space "nets" into orbit or shooting at the debris with lasers, it's very low tech. Plus to observers on Earth, tens of thousands of large bits of metal burning up will create a pretty good meteor shower.