The results are in, and NASA’s recent planetary defense proof-of-concept was a big success:
NASA smashed a spacecraft into an asteroid in an attempt to throw it off course. The mission succeeded beyond expectations, officials said. https://t.co/q8S33DdbW1
— NPR (@NPR) October 11, 2022
You may recall that the probe was crashed into one asteroid that orbits another asteroid. The goal was to shorten its orbital period, which is a very convenient visual measurement of imparted force. (In orbital mechanics, assuming classroom conditions, the time it takes to do a full orbit is a function of the satellite’s speed, and vice-versa, so we can determine the change in speed by the change in period, and from that extrapolate the effect of the impact.)
According to the NASA press release, they really smacked the crap out of that thing:
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 are two reasons for this discrepancy. First, we only have an estimate for the asteroid’s mass. Second, and more importantly, the surface composition of the asteroid was unknown. If it had been a solid block of iron-nickel, and remained fully intact, the only force acting upon it would have been that of the probe’s impact. This was not the case–the collision released a considerable amount of ejecta, surface material that flew away from the impact site. Since every action has an equal and opposite reaction, this served to amplify the force of the impact. We’ll know more about how this worked in the experiment, and what that means for the future, as the scientists continue crunching the numbers. In the meantime, let’s hope that any troublemakers lurking out in the dark have received the message:
Afternoon open thread!