While You Were Sleeping

Early this morning the asteroid '2009 DD45' passed very close to Earth.  Well, within 72,000 km anyway, about twice the height of our geosynchronous satellites.

Discovered only 3 days ago, this asteroid is estimated to have a diameter of approximately 35 metres and was closing on the Earth at approximately 8 kilometres per second-- actually a bit slow for most asteroids.

Asteroids pass close to the Earth all the time, and frequently collide. Thirty five metres, however, is fairly big, and this can do a lot of damage.  No, it isn't the kind of asteroid that could end life on Earth by any means but depending on the density of the asteroid and the angle of approach it could cause a fair bit of local damage. In 1908 an asteroid of similar size leveled over 200 square kilometres of forest in Tunguska, Russia.

Slow moving asteroids tend not to explode in the atmosphere which is what caused so much damage in the Tunguska event.  However, the final crater from an impact with an asteroid of this size (assuming it was iron) would be almost a kilometre across.  

Tunguska size impacts are expected to occur about once every hundred years or so.  Not to worry though, Tunguska happened 101 years ago.  Hmmmmm.

If the physics of asteroid impacts interest you (and by physics I mean damage), take a look at the webpage created by Marcus, Melosh, and Collings.   

Photo Credit: Asteroid Ida, Galileo Spacecraft, Astronomy Picture of the Day (June 29, 1997)