Later today (at 13:44 UTC), a small piece of space rock will pass close to earth.
The piece of rock in question is known as K09D45D, or 2009 DD45 for short, and is classified as a small asteroid.
In this context, 'small' means about 30m across. That's a fair-sized chunk of rock, and at a closing speed of around 10 km/sec it has a lot of kinetic energy.
Nevertheless, the rock will be up above most communications satellites when it flies by, roughly 65 000 km above Tahiti.
The rock was only discovered a couple of days ago, on 27 Feb, when it was barely visible, even to a large telescope. Then, Australian Rob McNaught alerted the Siding Spring Survey team, after finding the object using the 0.5-m Uppsala Schmidt Telescope at Siding Spring Observatory, New South Wales, Australia.
This early warning gave us, the earth-bound inhabitants of this planet, about three days' notice to identify the object and then take action.
That is, by current standards, a lot of warning. Such objects are, by their nature small and dark and difficult to spot.
There is no danger of a collision.
But if the orbital track were slightly different, the consequences would have been dire.
Astronomers think the 1908 Tunguska event was caused by a similar sized, 'small asteroid.'
source