The world is still vulnerable to a potentially catastrophic asteroid strike, according to President Barack Obama’s chief science adviser.

NASA has made substantial progress in finding the asteroids that pose the biggest threat to Earth, but there’s still a lot of work to do, said John Holdren, director of the White House’s Office of Science and Technology Policy.

“We are not fully prepared, but we are on a trajectory to get much more so,” Holdren said today (Sept. 14) at NASA’s Goddard Space Flight Center, during a discussion of the agency’s planned Asteroid Redirect Mission (ARM). [Images: Potentially Dangerous Asteroids]

Holdren cited the February 2013 meteor explosion over the Russian city of Chelyabinsk and the 1908 Tunguska air-burst as reasons to take the asteroid threat seriously.