Planetary Defense

Planetary Defense at NASA

Near-Earth objects (NEOs) are asteroids and comets that orbit the Sun like the planets, but their orbits can bring them into Earth’s neighborhood - within 30 million miles of Earth’s orbit. Planetary defense is “applied planetary science” to address the NEO impact hazard.

NASA established the Planetary Defense Coordination Office (PDCO) to manage its ongoing mission of planetary defense. The PDCO:

  • Provides early detection of potentially hazardous objects (PHOs) – the subset of NEOs whose orbits predict they will come within 5 million miles of Earth’s orbit; and of a size large enough (30 to 50 meters) to damage Earth’s surface;
  • Tracks and characterizes PHO's and issues warnings of the possible effects of potential impacts;
  • Studies strategies and technologies for mitigating PHO impacts; and
  • Plays a lead role in coordinating U.S. government planning for response to an actual impact threat.


The PDCO sponsors projects through its Near-Earth Object (NEO) Observations Program that employ a variety of ground and space based telescopes to search for NEOs, determine their orbits, and measure their physical characteristics. NASA is developing the NEO Surveyor space telescope optimized for NEO search and characterization to accelerate the discovery of the currently undetected NEOs.

Vapor trail from Chelyabinsk meteor event


The PDCO is responsible to provide timely and accurate information to the government, the media, and the public on close approaches to Earth by potentially hazardous objects (PHOs) and any potential for impact. If any PHO is found to pose a significant chance of impacting Earth (greater than 1 percent over the next 50 years), the PDCO will provide notification messages for NASA to send to the Executive Office of the President, the U.S. Congress, and other government departments and agencies.

(Image Credit: Alex Alishevskikh)

Planetary Defense Components-


The PDCO works with other government agencies to develop and update a National NEO Preparedness Strategy and Action Plan. The PDCO also provides expert input on the nature and effects of asteroid impacts to the Federal Emergency Management Agency (FEMA), so that adequate emergency response can be prepared in the event of a PHO impact that is not possible to avoid.

The PDCO also coordinates efforts with the space agencies of other nations as a member of the multinational International Asteroid Warning Network and the Space Missions Planning Advisory Group, under the endorsement of the United Nations Committee on the Peaceful Uses of Outer Space. NASA reorganized its Near Earth Object Observations Program and established a Planetary Defense Coordination Office in January 2016 in response to the NASA Office of Inspector General’s 2014 report, “NASA’s Efforts to Identify Near-Earth Objects and Mitigate Hazards.”

DART with propulsion and asteroids


The PDCO sponsors studies of technologies and techniques for deflecting an asteroid off a predicted impact course with Earth. It is developing missions to demonstrate those technologies and determine their effectiveness in the event that these techniques must be utilized against a predicted asteroid impact threat.

Double Asteroid Redirection Test (DART)

DART is a spacecraft designed to impact an asteroid as a test of technology. DART’s target asteroid is NOT a threat to Earth. This asteroid system is a perfect testing ground to see if intentionally crashing a spacecraft into an asteroid is an effective way to change its course, should an Earth-threatening asteroid be discovered in the future.

DART spacecraft and asteroid


DART is the first-ever mission dedicated to investigating and demonstrating one method of asteroid deflection by changing an asteroid’s motion in space through kinetic impact. This method will have DART deliberately collide with a target asteroid—which poses no threat to Earth— in order to change its speed and path. DART’s target is the binary, near-Earth asteroid system Didymos, composed of the roughly 780-meter (2,560-foot) -diameter “Didymos” and the smaller, approximately 160-meter (530-foot)-size “Dimorphos,” which orbits Didymos. DART will impact Dimorphos to change its orbit within the binary system, and the DART Investigation Team will compare the results of DART’s kinetic impact with Dimorphos to highly detailed computer simulations of kinetic impacts on asteroids. Doing so will evaluate the effectiveness of this mitigation approach and assess how best to apply it to future planetary defense scenarios, as well as how accurate the computer simulations are and how well they reflect the behavior of a real asteroid.

DART and Asteroids

Key Objectives

DART is a test of our ability to achieve a kinetic impact on an asteroid and observe the asteroid’s response. After DART’s kinetic impact with its target asteroid Dimorphos, an investigation team will measure how much the impact changed the asteroid’s motion in space using telescopes on Earth. This mission engages the international planetary science community and embraces worldwide cooperation to address the global issue of planetary defense.

DART’s Mission Objectives:

  • Demonstrate a kinetic impact with Dimorphos.
  • Change the binary orbital period of Dimorphos.
  • Use ground-based telescope observations to measure Dimorphos’ period change before and after impact.
  • Measure the effects of the impact and resulting ejecta on Dimorphos.

DART Thruster

Near-Earth Object Observations Program

The key element of NASA’s Planetary Defense effort is the Near-Earth Object (NEO) Observations Program, which is composed of projects to find, track, and characterize NEO's.

Perseoid Meteor Shower


The current congressionally directed objective of the NEO Observations Program is to find, track, and characterize at least 90 percent of the predicted number of NEOs that are 140 meters and larger in size–larger than a small football stadium–and to characterize a subset representative of the entire population. Objects of this size and larger pose a risk to Earth of greatest concern due to the level of devastation an impact would cause, and should continue to be the focus of global search efforts. While no known asteroid larger than 140 meters in size has a significant chance to hit Earth for the next 100 years, less than half of the estimated 25,000 NEOs that are 140 meters and larger in size have been found to date.

IRTF Observatory

Find and Observe

The NEO Observations Program sponsors projects that make use of telescopes around the world to search for NEOs, track them across the sky to determine their orbits, and gain information on their sizes, shapes, and composition.

The Minor Planet Center (MPC) is the internationally agreed-to public archive of small-body orbit data submitted by observers from around the world. The MPC notifies observers worldwide about NEO discoveries so that timely follow-up observations can be collected for identification, and orbit computation. The MPC is sanctioned by the International Astronomical Union and supported by the PDCO as a subnode of NASA’s Planetary Data System Small Bodies Node.

asteroid population

Predict the Orbit

The Center for Near-Earth Object Studies (CNEOS) computes high-precision orbit paths for NEOs from positions reported to the Minor Planet Center. CNEOS computes orbits for new asteroid discoveries and performs long-term analyses of possible future positions of hazardous asteroids relative to Earth to determine and warn of any impact hazard. CNEOS computes impact time and location in the event of a predicted impact. The Jet Propulsion Laboratory hosts CNEOS for the NEO Observations Program, and its website makes all orbit computation public.

Media Contacts and Information

NASA Newsroom: 202-358-1600 (Press Office Hours: 8:00am - 5:00pm EST)
Public Inquiries: 202-358-0001

Planetary Defense Coordination Office, NASA Headquarters
Karen Fox 301-286-6284
Joshua Handal 202-358-2307

DART, NASA Headquarters
Karen Fox 301-286-6284
Joshua Handal 202-358-2307
Alana Johnson 202-358-1501

Center for Near Earth Object Studies, Jet Propulsion Laboratory
Ian O'Neill 818-354-2649

​ Meteors, Meteor Showers—Meteoroid Environments Office, Marshall Space Flight Center
Molly Porter 256-544-2771

@AsteroidWatch on Twitter
Joshua Handal 202-358-2307
Click here to learn more about Planetary Defense

NASA reorganized its Near Earth Object Observations Program and established a Planetary Defense Coordination Office in January 2016 in response to the NASA Office of Inspector General’s 2014 report, “NASA’s Efforts to Identify Near-Earth Objects and Mitigate Hazards.”