This asteroid, 2014 DX110, is estimated to be about 100 feet (30 meters) across. Its closest approach to Earth will be at about 217,000 miles (about 350,000 kilometers) from Earth at about 1 p.m. PST (4 p.m. EST) on March 5. The average distance between Earth and its moon is about 239,000 miles (385,000 kilometers).
NASA detects, tracks and characterizes asteroids and comets using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them and identifies their close approaches to determine if any could be potentially hazardous to our planet.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.
More information about asteroids and near-Earth objects is at: http://www.jpl.nasa.gov/asteroidwatch.