We Moved an Asteroid. One Number Is Still Missing

On 26 September 2022, humans changed the motion of a natural object in space for the first time. It worked, but how well it worked depends on one number that nobody has measured: how much the asteroid weighs. NASA's DART spacecraft hit the small asteroid Dimorphos and shortened its orbit by about 33 minutes. ESA's Hera spacecraft is now on its way back to weigh it. This video explains what was hit, what changed, why the missing mass matters for planetary defence, and what Hera is expected to find. We cover why a pair of asteroids works like a stopwatch, how DART flew itself for the last hours, the 73-second success threshold, ejecta and the momentum enhancement factor (beta), the reported range of beta from about 2.2 to 4.9, the change in shape and the reported tiny change in the pair's path around the Sun, Hera's instruments and its cubesats Milani and Juventas, and a clear list of what is confirmed, what is estimated and what is still unknown. If you could ask Hera to measure one more thing on that asteroid, other than its weight, what would it be? Tell us in the comments. Music: Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 - http://creativecommons.org/licenses/b... Sources: NASA, ESA, JPL, Johns Hopkins APL and peer-reviewed research. Where a question is still open, this video says so. Arrival dates and later results are reported plans and may change. Hera's schedule is ESA's plan, not a promise. Footage is NASA public-domain imagery; some animations are artist concepts or visualisations, not photographs of the event. #NASA #DART #PlanetaryDefense