Dimorphos, a small moonlet that is part of the Near- Earth Asteroid Didymos, was hit by the Double Asteroid Redirection Test on September 26th. The purpose was to test a planetary defense technique where a spaceship collides with a potentially hazardous asteroid to change course. The impact of DART changed Dimorphos' orbital period by 33 minutes and caused tons of rock to be ejected from its surface.
NASA has been watching the cloud of ejected particles since the collision to see how it has changed. The purpose of this is to better understand what DART achieved at the impact site, how much of it was delivered, and how much was due to the recoil of the ejection. The DART team gave the preliminary analysis of their findings at the fall meeting of the AGU.
The program scientist for DART was present at the briefing. He related it in a NASA press statement.
“What we can learn from the DART mission is all part of a NASA’s overarching work to understand asteroids and other small bodies in our Solar System. Impacting the asteroid was just the start. Now we use the observations to study what these bodies are made of and how they were formed – as well as how to defend our planet should there ever be an asteroid headed our way.”
A detailed analysis of all the science and engineering data that was focused on measuring the momentum transfer of the DART spacecraft was included in the report. Predicting momentum transfer is important to planning future impact missions in the event that an asteroid hits Earth. Estimating the lead time needed to push an asteroid off its path is part of the process.
The team discovered that Didymos and Dimorphos have the same compositions. Both are composed of chondrite, rocky material that formed from dust and small grains in the early Solar System, the same material that can be found in meteorites. The majority of the reflected sunlight came from the double-asteroid in the days after the impact. Solar radiation pressure stretched the ejected stream into a twin tail, similar to comets.
About the same weight as a cargo ship, DART's impact displaced over a thousand metric ton of chondrite rock into space. The data was combined with information on the moonlet. The Italian Space Agency (ASI) contributed to the Light Italian CubseSat imagery of asteroids.
If Didymos and Dimorphos have the same densities, the team calculated the DART impact's effect on the recoil. They found that the total energy of the impact and ejected objects was 3.6 times greater than if the asteroid had absorbed the craft. The DART investigation team is led by Andy Cheng from theJHUAPL.
“Momentum transfer is one of the most important things we can measure, because it is information we would need to develop an impactor mission to divert a threatening asteroid. Understanding how a spacecraft impact will change an asteroid’s momentum is key to designing a mitigation strategy for a planetary defense scenario.”
The DART test showed that the technique can be used to divert an asteroid. The next step is to apply this knowledge so that the technique can be tested further. The success of these tests could have a huge impact on the future of life on Earth.
There is further reading on NASA.