Planetary Defense Coordination Office is a planetary defense organization within NASA's Planetary Science Division. Its mission is to lead the coordination of interagency and intergovernmental efforts to plan responses to potential impact threats. Announced by NASA in January 2016, it is given the job of cataloging and tracking potentially hazardous  near-Earth objects (NEO), such as asteroids and comets, which are larger than 30 to 50 m in diameter (compare to the 20-m Chelyabinsk meteor) and coordinating an effective threat response and mitigation effort. 
There are two basic types of objects of concern,
near-Earth objects (NEO's) and potentially hazardous objects (PHA's). NASA, in cooperation with the Jet Propulsion Laboratory (JPL), have worked, various, impact-threat scenarios, in order to learn the best approach to the threat of an incoming impactor. The office will continue to use the polar orbiting infrared telescope NEOWISE to detect any potentially hazardous object.
 Double Asteroid Redirection Test (DART) is the first planetary defense mission of NASA.
Since 2016, this office is headed by Lindley Johnson as NASA’s Planetary Defense Officer and Program Executive of the Planetary Defense Coordination Office (PDCO).
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"Double Asteroid Redirection Test". Johns Hopkins University Applied Physics Laboratory . Retrieved . February 18, 2021 This article incorporates text from this source, which is in the public domain .
"PDCO Organization". . NASA
David, Leonard (January 5, 2021). "Defending Earth against dangerous asteroids: Q&A with NASA's Lindley Johnson". . Space.com
NASA’s New Planetary Defense Office planetary.org