I hope everyone ducked this morning, as a small asteroid passed within 40,000 miles (64,000 km or 1/5th the distance to the Moon) of the Earth’s surface. The asteroid, named 2009 DD45, was discovered by the Siding Spring Survey on the morning of February 27. The Siding Spring Survey hunts for potentially hazardous asteroids and comets from the Siding Spring Observatory in Australia. Though operated in Australia the project is funded by NASA and based out of Arizona.
At its brightest the asteroid got as bright as magnitude 10-11. That is no where near bright enough to be seen without a telescope. Below is a video of 2009 DD45 moving rapidly through a star field. The video was taken by Australian amateur astronomer Dave Herald. DD45 is the star moving from the middle of the right edge of the field to the upper left corner of the field.
Though small the asteroid is still a sizeable 15-50 meters across (that’s 60 to 150 feet across). The reason for the uncertainty is because all we know about the asteroid is that is a certain brightness. But we don’t know how reflective the object is. Asteroids come in different types, some can reflect back ~50% of the sunlight that strikes them (that would make the DD45 smaller at ~15 meters) and others reflect are very dark and reflect no more than ~5% of the sunlight (that would make DD45 larger at ~50 meters).
If the asteroid had hit the Earth, it would most likely had exploded in the atmosphere. The explosion would still create a significant shock wave that would have done damage to the unlucky people, buildings and trees below it. Something similar occurred 101 years ago in Tunguska (Siberia).
There is no reason to worry about 2009 DD45. Not only is it now moving away from Earth it is not predicted to be on a collision course for the rest of the century.
A Sky and Telescope article about the fly-by can be found here.