Asteroid watchers are buzzing about a small object called 2010 AL30. First spotted on Sunday, it will speed past the Earth at midday London time on Wednesday, missing the planet by a mere 125,000 kilometres, just a third of the distance to the moon.

Astronomers had just two days' warning that the asteroid was headed this way. But at a mere 10 to 15 metres, the object would have been far from asteroidal Armageddon even if it had hit Earth. Think instead of the perils posed by the re-entry of the nearly 100-tonne US Skylab over Australia in 1979.

So far little is known about the object beyond its brightness and path. Initial calculations showing that it was on a one-year orbit around the sun led to suggestions that it might be a long-lost piece of space junk. However, that seems unlikely given that its orbit is elongated (see image), taking it from inside Venus almost to Mars.

Orbital calculations predict that 2010 AL30 will have a series of close encounters with Venus as well as with the Earth. Tomorrow's encounter will change its path. "The present orbit is just a momentary coincidence, and will be quite different after tomorrow's close approach," says Germany, Russia, Italy and Spain.

Yet despite the headlines, 2010 AL30 is far from a record-setter. It places 26th on the Jet Propulsion Laboratory's list of the closest observed asteroid approaches to the Earth. Harris said in an email that similar objects come this close to Earth about twice every month, mostly unseen. When it makes its closest approach, it will be about as bright as Pluto (14th magnitude), so amateur astronomers will be able to track it as it speeds across the sky toward the sun. Astronomers also will be watching with radar to see how the Earth's gravity will change the asteroid's orbit.

New Scientist