Although the chance of an asteroid impacting Earth is small, even a relatively small asteroid of about 500 feet (about 150 meters) across carries enough energy to cause widespread damage around the impact site. NASA leads efforts in the U.S. and worldwide both to detect and track potentially hazardous asteroids and to study technologies to mitigate or avoid impacts on Earth. If an asteroid were discovered and determined to be on a collision course with Earth, one response could be to launch a "kinetic impactor"—a high-velocity spacecraft that would deflect the asteroid by ramming into it, altering the asteroid's orbit slightly so that it misses Earth. NASA's Double Asteroid Redirection Test (DART) will be the first mission to demonstrate asteroid deflection using a kinetic impactor. 

DART will test kinetic impactor technology by targeting a double asteroid that is not on a path to collide with Earth and therefore poses no actual threat to the planet.

Chinese astronauts on Thursday beamed back a science lesson from the country's under-construction space station.

The lecture focused on physics, aiming to illustrate how the weightless environment affects buoyancy, the movement of objects and optics.

NASA's newest X-ray observatory rocketed into orbit Thursday to shed light on exploded stars, black holes and other violent high-energy events unfolding in the universe.