Tag Archives: planetary defense

NASA’s DART spacecraft impact measurably redirected the asteroid Dimorphos

Peter Lobner, updated 28 July 2023

NASA’s Double Asteroid Redirection Test (DART), which was launched on 24 November 2021, was the first test of a technology for defending Earth against potential asteroid or comet hazards. DART’s target was the small “moonlet” named Dimorphos orbiting the larger near-Earth asteroid Didymos, which itself is only a half mile in diameter.  You can explore at the Didymos – Dimorphos binary system on NASA’s Solar System Exploration webpage here: https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/didymos/in-depth/

Simulation of the Didymos – Dimorphos binary system. 
Source: NASA’s Solar System Exploration
Actual view of the Didymos – Dimorphos binary system as 
DART approached impact with Dimorphos (background). 
Source: NASA / JHAPL

The goal is for the DART spacecraft was to strike the moonlet Dimorphos at high speed while being trailed by another small spacecraft, the Italian Space Agency’s (ASI) cubesat, dubbed LICIACube, that would directly observe the encounter and report back to NASA and ASI. 

By comparing pre- and post-impact measurements made with powerful Earth-based and orbiting telescopes, the NASA / Johns Hopkins Applied Physics Lab (JHAPL) team could determine what changes occurred to Dimorphos’ orbit around Didymos. These results will help assess the feasibility of using a high-energy impactor as a tool for deflecting the trajectory of an asteroid, particularly one that represents a significant risk to Earth.  Learn more about the DART spacecraft and its mission objectives on NASA’s Planetary Defense Coordination Office website here: https://www.nasa.gov/planetarydefense/dart/dart-news

NASA successfully guided DART to a collision with Dimorphos on 26 September 2022.   You can watch the final five minutes of DART’s approach to the Didymos – Dimorphos binary system up to the final image before impact here: https://www.nasa.gov/feature/dart-s-final-images-prior-to-impact

DART closeup image of Dimorphos moments before impact.
Source: NASA / JHAPL
ASI’s LICIACube image just before its closest approach to Dimorphos (background). The debris plume cast off from Dimorphos after DART’s impact is clearly visible. Didymos is in the foreground. Source: ASI / NASA

The Hubble Space Telescope was used to capture images of the impact.  The NASA/ESA Hubble Space Telescope team reported:

“The Hubble movie starts at 1.3 hours before impact. The first post-impact snapshot is 20 minutes after the event. Debris flies away from the asteroid in straight lines, moving faster than four miles per hour (fast enough to escape the asteroid’s gravitational pull, so it does not fall back onto the asteroid). The ejecta forms a largely hollow cone with long, stringy filaments.

At about 17 hours after the impact the debris pattern entered a second stage. The dynamic interaction within the binary system started to distort the cone shape of the ejecta pattern. The most prominent structures are rotating, pinwheel-shaped features. The pinwheel is tied to the gravitational pull of the companion asteroid, Didymos. 

Hubble next captures the debris being swept back into a comet-like tail by the pressure of sunlight on the tiny dust particles. This stretches out into a debris train where the lightest particles travel the fastest and farthest from the asteroid. The mystery is compounded later when Hubble records the tail splitting in two for a few days.”

8 October 2022 photo by the Hubble Space Telescope shows Dimorphos with its debris tail. Source: NASA/ESA/STScI/Hubble

The results are in, and on 1 March 2023, the NASA / JHAPL team reported a much greater change to Dimorphos’ orbit than originally expected.

“…the investigation team, led by Cristina Thomas of Northern Arizona University, arrived at two consistent measurements of the period change from the kinetic impact: 33 minutes, plus or minus one minute. This large change indicates the recoil from material excavated from the asteroid and ejected into space by the impact (known as ejecta) contributed significant momentum change to the asteroid, beyond that of the DART spacecraft itself.”


After the success of the DART mission, maybe the U.S. Planetary Defense Officer will have fewer sleepless nights, but this is only the first small, but successful step toward an operational planetary defense system.

28 June 2023 update: Hubble sees bolder swarm surrounding Dimorphos

In June 2023, NASA reported that the Hubble Space Telescope had observed a swarm of 37 boulders that appears to have been knocked loose from Dimorphos upon impact. 

An image of the impacted asteroid, Dimorphos, with drawn-in circles around the areas where boulders have been detected. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). Source: NASA, ESA, David Jewitt (UCLA); Alyssa Pagan (STScI)

NASA reported: 

“The 37 free-flung boulders range in size from three feet to 22 feet across, based on Hubble photometry. They are drifting away from the asteroid at little more than a half-mile per hour – roughly the walking speed of a giant tortoise. The total mass in these detected boulders is about 0.1% the mass of Dimorphos…… The boulders are most likely not shattered pieces of the diminutive asteroid caused by the impact. They were already scattered across the asteroid’s surface, as evident in the last close-up picture taken by the DART spacecraft just two seconds before collision, when it was only seven miles above the surface.”

The loose composition of the surface of Dimorphos can be seen in this last complete image just prior to DART impact. Source: NASA, APL

For more information


Relax, the Planetary Defense Officer has the Watch

Peter Lobner

On 7 January 2016, NASA formalized its ongoing program for detecting and tracking Near-Earth Objects (NEOs) by establishing the Planetary Defense Coordination Office (PDCO). You can read the NASA announcement at the following link:


PDCO is responsible for supervision of all NASA-funded projects to find and characterize asteroids and comets that pass near Earth’s orbit around the sun. PDCO also will take a leading role in coordinating interagency and intergovernmental efforts in response to any potential impact threats. Specific assigned responsibilities are:

  • Ensuring the early detection of potentially hazardous objects (PHOs), which are defined as asteroids and comets whose orbits are predicted to bring them within 0.05 Astronomical Units (AUs) of Earth (7.48 million km, 4.65 million miles); and of a size large enough to reach Earth’s surface – that is, greater than 30 to 50 meters (98.4 to 164.0 feet);
  • Tracking and characterizing PHOs and issuing warnings about potential impacts;
  • Providing timely and accurate communications about PHOs; and
  • Performing as a lead coordination node in U.S. Government planning for response to an actual impact threat.

As you can see in the following organization chart, PDCO is part of NASA’s Planetary Science Division, in the agency’s Science Mission Directorate in Washington D.C.  PDCO is led by Lindley Johnson, longtime NEO program executive, who now has the very impressive title of “Planetary Defense Officer”.

Planetary Defense Coordination OfficeSource: NASA PDCO

You can find out more at the PDCO website at the following link:


The PDCO includes the Near Earth Object (NEO) Observation Program, which was established in 1998 in response to a request from the House Committee on Science that NASA find at least 90% of 1 km (0.62 mile) and larger NEOs. That goal was achieved by end of 2010.

The NASA Authorization Act of 2005 increased the scope of NEO objectives by amending the National Aeronautics and Space Act of 1958 (“NASA Charter”) by adding the following new functional requirement:

 ‘‘The Congress declares that the general welfare and security of the United States require that the unique competence of the National Aeronautics and Space Administration be directed to detecting, tracking, cataloging, and characterizing near-Earth asteroids and comets in order to provide warning and mitigation of the potential hazard of such near-Earth objects to the Earth.’’

 This was further clarified by stating that NASA will:

“…plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near-Earth objects equal to or greater than 140 meters (459 feet) in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the Survey program to achieve 90 percent completion of its near-Earth object catalog within fifteen years (by 2020)”

The contractors supporting the NASA NEO Observation Program are Jet propulsion Laboratory (JPL), Massachusetts Institute of Technology (MIT) / Lincoln laboratory, Smithsonian Astrophysical Observatory, University Space Research Association, University of Arizona, and University of Hawaii / Institute of Astronomy.

Once detected, NEO orbits are precisely predicted and monitored by the Center for NEO Studies (CNEOS) at JPL. Their website is at the following link:


The catalog of known NEOs as of 3 November 2015 included 13,206 objects. NASA reports that new NEOs are being identified at a rate of about 1,500 per year. Roughly half of the known NEOs – about 6,800 – are objects larger than 140 meters (459 feet) in diameter. The estimated population of NEOs of this size is about 25,000. Current surveys are finding NEOs of this size at a rate of about 500 per year.  Recent encounters with NEOs include:

  • Asteroid 2015 TB145, the “Halloween Pumpkin”
    • Roughly spherical, about 610 meters (2,000 feet) in diameter
    • Detected 10 October 2015, approaching from the outer solar system, 21 days before closest approach
    • Closest approach occurred on 31 October 2015 at a distance of 310,000 miles (1.3 times the distance to the Moon) at a speed of about 78,000 miles an hour.
  • Asteroid airburst near Chelyabinsk, Russia
    • Airburst occurred 15 February 2013
    • Object estimated to be about 19 meters in diameter
    • Approached from the inner solar system; not detected before airburst
    • Peter Brown at the University of Western Ontario, estimated the energy of the Chelyabinsk airbust at 400 to 600 kilotons of TNT.  You can read this analysis in at the following link:


Another result of the NEO Observation Program is the following map of data gathered from 1994-2013 on small asteroids impacting Earth’s atmosphere and disintegrating to create very bright meteors, technically called “bolides” and commonly referred to as “fireballs”.  Sizes of orange dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size.  You can see a rather uniform distribution of these fireballs over the surface of the Earth.

bolide_events_1994-2013 Source: NASA NEO Observation Program

In September 2014, the NASA Inspector General published the report, “NASA’s Efforts to Identify Near-Earth Objects and Mitigate Hazards,” which you can download for free at the following link:


Key findings were the following:

  • Even though the Program has discovered, categorized, and plotted the orbits of more than 11,000 NEOs since 1998, NASA will fall short of meeting the 2005 Authorization Act goal of finding 90 percent of NEOs larger than 140 meters (459 feet) in diameter by 2020.
  • ….we believe the Program would be more efficient, effective, and transparent were it organized and managed in accordance with standard NASA research program requirements

You will find an NEO Program update, including a reference to the new Planetary Defense Coordination Office, presented by Lindley Johnson on 8 November 2915 at the following link:


So, what will we see in the years ahead as technology is explored and techniques are developed to defend Earth against a significant NEO impact? There have been many movies that have tried to answer that question, but none offered a particularly good answer.

Asteroid movies 2Asteroid movies 1 Source: Google

In 1968, Star Trek explored this issue in Season 3, Episode 3, “The Paradise Syndrome”. Ancient aliens had left a planetary defense device to protect a primitive civilization against their equivalent of NEOs. Only the intervention of Capt. James T. Kirk restored the device to operation in time to deflect an incoming asteroid and save the indigenous civilization.

Star Trek - The Paradise Syndrome 1 Source: memory-alpha.wiki.comStar Trek - The Paradise Syndrome 2 Source: technovelgy.com

Our new Planetary Defense Officer has a comparable responsibility on Earth, but without the benefits of special effects.

In 2010, National Academies Press published, “Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies.” This report explores civil defense mitigation action and three basic defense techniques:

  • Slow push-pull methods
  • Kinetic impact methods
  • Nuclear methods

If you have a MyNAP account, you can download this report for free at the following link:


NAP Defending Planet Earth Source: NAP