Via NASA Watch, Space Flight Now is reporting an astonishing collision between two satellites: an old Russian satellite and one of the Iridium communications satellites:
"They collided at an altitude of 790 kilometers (491 miles) over northern Siberia Tuesday about noon Washington time," said Nicholas Johnson, NASA's chief scientist for orbital debris at the Johnson Space Center in Houston. "The U.S. space surveillance network detected a large number of debris from both objects."
It sounds like a curiosity that this particular collision happened, but unfortunately there is reason to believe that collisions will become more and more common. In the long-term, it may become so dangerous that low-earth orbit is useless.
The European Space Agency (ESA) has created images and movies about space debris:
Here's what Physics Today has to say about the threat last year:
The density of debris is fast approaching supercriticality, according to David Wright of the Union of Concerned Scientists, which maintains a satellite database tracking all those bits of debris. This situation could result from the destruction of an orbiting object into many smaller fragments of debris, initiating a chain reaction as that debris collides with other satellites in nearby orbits, breaking them into fragments in turn and compounding the problem further.
At high altitudes, the debris can stay in orbit for decades, accumulating to the point where there is a much higher risk of collisions with satellites. In fact, it may already be too late: Wright cited a 2006 study by NASA’s Orbit Debris Program that found certain parts of space particularly the 900 to 1000 km band, or Lower Earth Orbit (LEO) have already reached supercritical debris densities. NASA estimates that an active satellite in LEO will collide with a piece of debris larger than 1 centimeter every five to six years.
What's "supercriticality?" It's the idea that once there is enough debris in orbit, a chain reaction of collisions will set in that destroys existing satellites. Each destroyed satellies, of course, makes hundreds of dangeous pieces of debris, which in turn can destroy more.
Everyone launching satellites need to take steps to reduce debris. Most importantly, no one should duplicate the astonishingly irresponsible Chinese anti-satellite missile test.
Update: If you would like to see the more technical but still accessible discussion of space debris, this is the full Physics Today 2007 article