For years now, experts have been warning about the danger of collisions with space junk in Earth orbit. There is so much "stuff" rattling around up there, both working and not, that it is almost inevitable that a collision will occur.
On Tuesday, the first such major collision happened, between an Iridium communications satellite and a Russian satellite. The collision occurred 490 miles above Siberia, and the resulting bits of broken satellite briefly posed a serious threat to the International Space Station, until it was shifted into a higher orbit. The risk to the ISS is now judged as "very small" by a NASA spokesperson.
The American satellite, part of the Iridium Satellite network (used to provide mobile phone service to people who roam outside cell phone networks - for example, to Antarctica), is described as weighing about 1,200 pounds, with a body that was 12 feet long (not counting the various rays and antennas). The Russians have not yet released information about their satellite which was destroyed. Iridium is tactfully describing it as "presumably non-functional."
The United States military is attempting to track all the pieces from the collision, with only some success. Some of the pieces are large, but many are very small - too small for radar - but not too small to cause serious damage to anything else in orbit.
The NASA spokesperson added that the "swarms of debris" could threaten the rest of Earth's network of satellites, in an "orbital chain reaction." Which, if it happened in a movie, would be pretty funny to watch. Not so funny if it happened in real life.