From the NASA press release:
Analysis of data obtained over the past two weeks by NASA’s Double Asteroid Redirection Test (DART) investigation team shows the spacecraft's kinetic impact with its target asteroid, Dimorphos, successfully altered the asteroid’s orbit. This marks humanity’s first time purposely changing the motion of a celestial object and the first full-scale demonstration of asteroid deflection technology.
Prior to DART’s impact, it took Dimorphos 11 hours and 55 minutes to orbit its larger parent asteroid, Didymos. Since DART’s intentional collision with Dimorphos on Sept. 26, astronomers have been using telescopes on Earth to measure how much that time has changed. Now, the investigation team has confirmed the spacecraft’s impact altered Dimorphos’ orbit around Didymos by 32 minutes, shortening the 11 hour and 55-minute orbit to 11 hours and 23 minutes. This measurement has a margin of uncertainty of approximately plus or minus 2 minutes.
Before its encounter, NASA had defined a minimum successful orbit period change of Dimorphos as change of 73 seconds or more. This early data show DART surpassed this minimum benchmark by more than 25 times.
There’s more at the link.
Here’s the NASA promo for the mission:
In case you missed it, here’s the images sent back by the DART spacecraft up until the moment of impact.
Why this matters:
The odds of an asteroid striking the Earth and causing significant damage are low — but not zero. Every day the Earth is struck by numerous bits of cosmic debris, most of which burn up in the atmosphere.
Few survive atmospheric entry to reach the ground, but occasionally some do. Every once in a while it can be spectacular and cause damage. The video below shows what a meteor estimated to weigh just tens of tons did when it broke up at low level in the air.
By coincidence a much larger chunk of space rock happened to be passing by at about the same time — and missed.
A meteor estimated at 6 miles in diameter hit the earth about 66 million years ago. It is now generally accepted as “the cause of the Cretaceous–Paleogene extinction event, a mass extinction of 75% of plant and animal species on Earth, including all non-avian dinosaurs.”
NASA has an actual Planetary Defense Coordination Office. (Not currently tied in with USSF, aka Space Force, although planetary defense would seem a logical mission in the future for the new branch of the military.)
The mission of NASA’s PDCO is relatively straightforward, if not necessarily simple to accomplish:
- 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.
Having advanced warning even of relatively small objects is not a bad thing to work on. The meteor that blew up over Russia did so in 2013. If it had taken place during the current conflict in Ukraine, the chances that it might have been taken for an attack on Russia could have led to serious if misguided retaliation. Timing is everything — especially in orbital mechanics.
How much lead time PDCO would have if it detected an incoming threat would be critical, depending on how large it was and for several other reasons. One is that it takes time to prepare a mission, from design to launch. Two is that it takes time to reach a PHO, depending on how far away it is and the shape/orientation of its orbit. Three is that the longer NASA would have to change the orbit of the incoming rock, it would allow more options.
The DART mission was to explore how a high-speed impact would work in practice. Although it succeeded, it was not just about changing the orbit of the target. It was demonstrating that the target could be hit in the first place — and finding out what would happen after impact.
Focus now is shifting toward measuring the efficiency of momentum transfer from DART’s roughly 14,000-mile (22,530-kilometer) per hour collision with its target. This includes further analysis of the "ejecta” – the many tons of asteroidal rock displaced and launched into space by the impact. The recoil from this blast of debris substantially enhanced DART’s push against Dimorphos – a little like a jet of air streaming out of a balloon sends the balloon in the opposite direction.
Depending on how close to Earth such an impact would take place, an expanding debris cloud might still be an issue. A longer lead time would allow for gentler measures. A small but constant force applied over a long enough time frame could shift the orbit of even a dinosaur killer asteroid.
Electric thrusters could be one way to accomplish that. Soft land a package with thrusters on the target, orient it so the thrust it produces can shift the orbit in the right direction, and that’s all that’s needed given enough time to work.
Another approach would be the gravity tractor — no beam involved. The minuscule gravitational attraction from a space craft maneuvering near a target would be sufficient to shift its orbit given enough time.
There’s a variety of different techniques that could be used to deflect an asteroid — but DART is the only one tested so far. None of them will be of use without finding and identifying possible hazards in a timely fashion, so that’s an essential first step.
Going beyond planetary defense, being able to shift the orbit of asteroids to more convenient locations might make it possible to start shifting to space-based resources, the Third Industrial Revolution of the late G. Harry Stine.
Here’s a Thomas Dolby composition N.E.O. (Near Earth Object) with vocals by Dr. Fiorella Terenzi from the video The Gate to the Mind’s Eye. (Entire video at link at the Internet Archive) You may recognize one clip from the opening of Deep Space Nine, and another possibly from Voyager.