Nature's Tiniest Space Junk

Using an experimental radar at the Marshall Space Flight Centre, scientists are monitoring tiny but hazardous meteoroids that swarm around our planet.

Our planet is surrounded by a swarm of alien invaders. They fly through space faster than a speeding bullet and they're nearly impossible to track with conventional ground-based radars.

Is Earth in peril? Is it time to head for the community storm shelter?

Not this time, say scientists. The interlopers are simply meteoroids, ever-present specks of dust shed by comets and asteroids. And they pose no danger to Earthlings other than occasional headaches suffered by satellite operators.

Most meteoroids are tiny - typical grains span just a few tenths of a millimetre and weigh less than 10^-4 grams. Nevertheless, meteoroids pack a considerable punch as they fly by Earth at speeds ranging from ~10 to 70 km/s (22,000 to 157,000 mph). A 10^-4 gm speck of dust racing along at 30 km/s carries about the same energy as a very high energy cosmic ray, ~3 x 10²⁰ electron volts. Collisions with high-speed space dust can electrify satellites, scrambling software and triggering mistaken control procedures.

So what can a beleaguered satellite operator do?

"Not much," says Rob Suggs, the Space Environments team leader at the Marshall Space Flight Centre Engineering Directorate. Meteoroids are so numerous they're impossible to avoid entirely. If ground controllers know when Earth is going to enter a dense swarm they can orient their craft to minimise cross section or point sensitive components away from the incoming particles. "They can also turn off high voltage power supplies, and avoid complex manoeuvres," added Suggs. "This is what we recommend when we give satellite operators our meteoroid forecasts."

Recurring annual meteor showers like the Leonids and Perseids are predictable. But what about times when Earth passes through an uncharted dust stream? There are plenty of examples in recent years of meteor flurries that took sky watchers and satellite operators by surprise.