NASA probe moves an asteroid

ZFor the first time in history, mankind has moved a celestial body. On September 26, the Dart (short for “Double Asteroid Redirection Test”) spacecraft had rammed the 163-metre-wide asteroid Dimorphos head-on. The crash was deliberately caused by the American space agency NASA and was observed from close by the Italian mini-probe “LiciaCube”. The mission was to find out whether asteroids can be deflected from their orbit in this way. Chunks between 140 and 1000 meters in size would cause severe regional to continent-wide devastation if they collided with the earth. Thousands of bodies in this caliber range are orbiting near Earth’s orbit, and only 40 percent of them may have been detected so far.

significantly reduced turnaround time

Two weeks after the impact, NASA announced on Tuesday evening that the experiment was successful. Since Dimorphos orbits like a small moon around a slightly larger asteroid called Didymos, the change in orbit could be verified by measuring the orbital period. Four optical telescopes in Chile and South Africa and two radio telescopes in California and West Virginia have now determined: Dimorphos’ orbital period around Didymos was reduced by 32 minutes from the original eleven hours and 55 minutes after the impact. The two asteroids, which are 1.3 kilometers apart, moved several tens of meters closer together.

This is far at the upper end of what modeling had previously suggested. The researchers had calculated that the orbital period would be reduced by between 73 seconds and several tens of minutes. However, it would also have been conceivable that the transfer of the kinetic energy of the 610-kilogram probe hitting the asteroid at 23,800 kilometers per hour would work too poorly to achieve an effect.

That was apparently not the case, and the researchers are now trying to find out why the effect was even so large. It’s still a bit early for more precise statements, said Tom Satler, program scientist for the mission, at a NASA press conference. “But it looks like the ejected material made a significant contribution to the impact the asteroid received — in addition to the direct impact from the impacting probe.”

Further observations should now show more details. This will continue for a few more months until the orbiting pair of asteroids has strayed too far from near-Earth. In doing so, says Satler, one also wants to find out whether and to what extent Dimorphos or its orbit around Didymos was set in rolling motion by the collision and how this will change over time. In no case, however, will the asteroid return to its original orbital parameters.

The consequences of NASA scientists’ intervention in the dynamics of this celestial body system will be permanent. There is also great interest in following up the generated debris cloud. Due to the very low gravity of the little Dimorphos, this settles very slowly. Last Saturday she was seen in a picture taken by the Hubble Space Telescope. However, the same image also shows a plume of fine-grained material stretching more than 10,000 kilometers, stretched by the radiation pressure of sunlight like a comet. In the meantime, this plume of dust has also split up. The reasons for this are still unclear.