Hopefully, transferring momentum—mass multiplied by velocity—from the spacecraft onto Dimorphus will change the Moon’s speed by a fraction of a percentage.
This will change the orbital period of Dimorphos around Didymus by several minutes, estimated to be between 3 and 10 minutes. This is enough for observation and measurement with telescopes on Earth. The press conference said Demorphos is now orbiting Didymus for 11 hours and 55 minutes, and if that time changes by 73 seconds, that’s enough to pass the test.
The researchers also want to measure momentum transfer so they have an idea of what it would take to deal with an Earth-threatening asteroid. Although it must be said that this depends on the distance at which the interference will occur. The best time to deflect a dangerous asteroid from its orbit is years, even decades, before it approaches Earth. After all, the further away it is, the less force is needed to sufficiently change its orbit.
To measure the impulse transmission, the researchers rely primarily on Italy’s LICIACube, a small spacecraft that travels using DART and is ejected 10 days before the collision. This cube will then follow DART and will also fly past the Dimorphus after impact. By doing so, it will send images to Earth of the impact and ejection, the material that was thrown out due to the impact.
The researchers expect tons of material to be thrown into space, possibly tens of tons, and they can calculate the impulse transmission using images from the LICIACube of those projectiles.
Observations with telescopes on Earth will follow at Dimorphus until February/March 2023 and the European Space Agency (ESA) is scheduled to launch Hera to Didymos in 2024. This spacecraft should reach the asteroid system in 2027 to see the consequences of the collision in more detail.
By the way, the orbit of the large asteroid Didymos will also change due to the collision, since the two asteroids are bound together by gravity, but since Demorphos is very small in proportion, this change will be too small to measure.
An English-language video from the Johns Hopkins University Applied Physics Laboratory about the mission.
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