Don't panic

By J.P. | LONDON

NASA's scientists have just announced that two asteroids are going to swish by today, within the moon's distance of Earth. One, called 2010 RX30 and measuring between 10 and 20 metres (32 and 65 feet) in diameter, will get as close as 0.6 lunar distances, or about 248,000 kilometres (154,000 miles) at precisely 9.51 am GMT. Just over 11 hours later, 2010 RF12, approximately two-thirds the size of the its bigger brother and following an independent orbit, will come even closer, some 0.2 lunar distances.

Mostly harmless

Don't start looking to hitch a ride on that alien spaceship just yet, though. Neither has a chance of hitting the planet. True, the lunar orbit, with an average radius of 384,403 kilometers, is puny in cosmic terms, but similar near-misses aren't all that uncommon. A 10-metre sized rock is expected to pass within lunar distance every day, on average. And once a decade, one is likely actually to strike Earth's atmosphere, though most of these would burn up on entry to the extent that they pose little or no threat. This would probably have been the fate of the 6 metre 2004 FU162 spotted on March 31st, 2004, just hours before the meteoroid whizzed by a mere 6,500 kilometres from Earth, setting a new record for the closest observed near miss.

Many celestial objects still pass unnoticed, though people are getting better at espying them. This amazing film by Scott Manley shows the locations of all known asteroids in the solar system, starting in 1980. We owe today's quarry to the Catalina Sky Survey near Tucson, Arizona, which discovered both objects last Sunday during a routine monitoring of the skies. Its researchers then alerted the Minor Planet Center in Cambridge, Massachusetts, which proceeded to calculate the preliminary orbits. The most notable thing about the two asteroids is that they will be visible with moderate-sized amateur telescopes. So, as Douglas Adams wisely advised, don't panic.

(Photo: NASA/JPL-Caltech)