Graphic by Jen Christiansen. Source: NASA Jet Propulsion Laboratory
Tens of thousands of near-earth objects—asteroids and comets—pass by our planet in regular orbits. A subset, known as potentially hazardous objects, could possibly hit us and are big enough to cause considerable damage if they did.
NASA’s Jet Propulsion Laboratory tracks these worrisome rocks in awesome detail. For example, the diagram below shows the Earth's position on February 7, 2011, and the five most recent close-approaches of hazardous objects leading up to that date.
All of JPL’s orbit data are available on an easy-to-use site, which includes tables showing past and future close approaches for all near-earth objects and highlights hazardous objects that will be closest to Earth in the upcoming weeks. The tables list size, brightness and velocity of every object, and the orbit diagrams—updated daily—include each object’s current position and distance from Earth.