Today, we got some hard numbers on the asteroids, comets and other objects whizzing through space near Earth.

Astrophysicist Amy Mainzer took a break from asteroid-hunting at JPL to answer a couple of our most burning questions about asteroids, comets, and whatever else is just over our heads. Among the questions she answered were just how likely an Armageddon-sized asteroid crash was ("The only asteroid we know of that's as big as Texas [Ceres] is parked safely and soundly in the Main Asteroid Belt and isn't going anywhere. Whew!"), just where Earth Trojan asteroids might come from ("there are some theories that postulate that they might be leftovers from the solar system's birth. But my guess is that they're more recent captures - kind of like a leaf that gets temporarily dragged into an eddy in a river, then eventually gets booted back out"), and also gave us some amazing information about just how much there is out there still left to find:

Right now, there are several surveys that are discovering near-Earth asteroids, and they're supported by a network of amateur and professional astronomers who keep track of them. The most productive survey to date in terms of total number of discoveries is the Catalina Sky Survey, along with PanSTARRS and LINEAR. The community is discovering about 1000 new near-Earth objects per year of all sizes, which means there are still a lot more out there left to find. With our team's work using the NEOWISE space-based infrared survey observations, we were able to make some estimates of how many objects are out there, and what fraction have been found. Our observations and calculations show that about 25% of near-Earth asteroids larger than 100 meters in diameter have already been discovered, and there are about 20,500 that are out there. We'd obviously like to do a more comprehensive survey, though, and that's why we proposed NEOCam!