NASA has set up a Planetary Defense Coordination Office - to defend the Earth from asteroids and comets that get too close for our comfort. The department, which includes the position of Planetary Defense Officer, is managed by the Planetary Science Division of the Science Mission Directorate at NASA Headquarters in Washington DC. And its mission includes the early detection of potentially hazardous objects (PHOs) - asteroids and comets which get within 0.05 Astronomical Units of Earth's orbit around the sun (7.5 million kilometers) and are large enough, greater than around 30 - 50 meters (98 - 164 feet), to reach the Earth's surface. They must also track and issue warnings on the minor planets, or even try to redirect them. If it's too late and space rubble is found hurtling towards the Earth's surface, the team will coordinate with the U.S. government to plan a response to an actual impact threat. More than 13,500 NEOs have been discovered to date and about 1,500 are detected each year. Asteroid detection, tracking and defense of our planet is something that NASA, its interagency partners, and the global community take very seriously," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate in Washington. "While there are no known impact threats at this time, the 2013 Chelyabinsk super-fireball and the recent 'Halloween Asteroid' close approach remind us of why we need to remain vigilant and keep our eyes to the sky."