NASA’s First-Ever Planetary Defense Test

NASA’s DART (Double Asteroid Redirection Test) targeted the asteroid moonlet Dimorphos, a small body just 530 feet (160 meters) in diameter. It orbits a larger, 2,560-foot (780-meter) asteroid called Didymos. Neither asteroid poses a threat to Earth.

The mission’s one-way trip confirmed NASA can successfully navigate a spacecraft to intentionally collide with an asteroid to deflect it, a technique known as kinetic impact.

With the asteroid pair within 7 million miles (11 million kilometers) of Earth, a global team is using dozens of telescopes stationed around the world and in space to observe the asteroid system. Over the coming weeks, they will characterize the ejecta produced and precisely measure Dimorphos’ orbital change to determine how effectively DART deflected the asteroid. The results will help validate and improve scientific computer models critical to predicting the effectiveness of this technique as a reliable method for asteroid deflection.

“This first-of-its-kind mission required incredible preparation and precision, and the team exceeded expectations on all counts,” said APL Director Ralph Semmel. “Beyond the truly exciting success of the technology demonstration, capabilities based on DART could one day be used to change the course of an asteroid to protect our planet and preserve life on Earth as we know it.”

Roughly four years from now, the European Space Agency’s Hera project will conduct detailed surveys of both Dimorphos and Didymos, with a particular focus on the crater left by DART’s collision and a precise measurement of Dimorphos’ mass.

15 thoughts on “NASA’s First-Ever Planetary Defense Test”

  1. They have shown they were able to collide with the asteroid. Whether they managed to deflect it remains to be seen over the coming weeks.

    This is particularly an issue with “rubble-pile”-type asteroids. Can we effectively transfer momentum to a majority of the mass of such an asteroid, or would any given impact merely deflect a fraction of the mass of the body?

    • Anelastic hit. Conservation of kinetic energy doesn’t apply, conservation of momentum does-
      Many million tons vs a fraction of a ton, kilometers per second become fractions of millimeters.

      • No, it’s fine for it to be inelastic. What I mean is that with a rubble pile, an impactor may deflect (i.e., impart its momentum to) only *some of the rubble* leaving part (perhaps the greater part) on the original trajectory.

        • I thought they were going for a multiplier effect. The plasma or dust cloud you can see can push the asteroid. The small size of the impact doesn’t transmit much energy to the ball of sand but exiting shock wave has a stronger effect. I’m not sure about that, Scott Manley did a YouTube video.
          Making a dust storm around an asteroid that catches sunlight might move it back.
          Tasting our theories is appropriate.

    • Creating even a very small deviation can, over long periods of time, create a substantial change in where the thing goes. The article mentions needing five years for a good deflection in some cases.

      I saw a plan somewhere to put a moderately small asteroid into such an orbit that it gives the Earth an almost undetectable nudge on each pass. Yet over the course of a billion years, done properly, it could be enough to move the Earth out past the orbit of Mars, potentially saving it from a steadily warming Sun.

  2. That approach video was incredible. Very cinematic.

    And the collision pictures taken from the cubesat, spot on.

    Seems Dimorphos was a pile of rubble, without any craters. Until today.

    Given the low gravity of Didymos, I wonder if the energy of the collision exceeds the potential energy of the moonlet’s orbit. In that case, they might have whacked it out of Didymos orbit.

    • The articles I saw that went into details of what was expected said that they expected the impact, at best, to slow the moonlet in its orbit by a fraction of a millimeter per second. (The articles stated the fraction, but I don’t recall it.) This would shorten the time it takes the moonlet to orbit the main asteroid from 12 hours to around 11 hours and 50 minutes, if I recall the numbers correctly.

      So, no, that little spacecraft had nowhere near the amount of energy needed to knock the moonlet free of the main asteroid.

      • Could have knocked some bits of it out of that orbit, though.

        I would think one of the things they wanted to learn was the degree to which such an impact would “splash” debris, vs efficiently transferring momentum to an intact asteroid.

        Ideally you want the target to hold together and get deflected as one entity, otherwise you’re just turning a bullet into a shotgun blast. But a light high speed projectile has a lot of kinetic energy relative to its momentum, so the “splash” potential is high.

        • I would imagine that turning it into a shotgun blast might be preferable to a bullet. A thousand 20 ton meteorites would be bad, but it wouldn’t be as bad as a single 20,000 ton meteorite screaming through the atmosphere.

          • Locally the bullet could be worse, globally the shotgun blast could be worse. It really depends on so many factors. Like whether the asteroid is large enough to punch through the crust and create a supervolcano.

            But it’s a lot easier for that bullet to miss…

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