text | Li Muzi
September 26, a vending-sized spacecraft will hit a 160-meter-diameter asteroid Dimorphos at a speed of 6 kilometers per second. This upcoming "violent" operation is the first field test of a planetary defense mission in human history, namely, NASA (NASA) dual asteroid redirection test (DART).
Image source: NASA
DART mission team recently observed the dual asteroid system Didymos for the first time, and the target asteroid Dimorphos is one of the small satellites . NASA hopes the collision pushes Dimorphos into orbit closer to Didymos, reducing its nearly 12-hour runtime by a few minutes.
In the future, similar impacts can cause threatening asteroids to turn. But new simulations and laboratory experiments show that the success of the mission depends on whether these asteroids are a solid rock or a loose pile of gravel.
Answer will be revealed from the craters and ejections generated by the impact, which may determine the difficulty of impacting the asteroid.
Compared with the larger planets that previously triggered mass extinction events, double asteroids are thousands of times more likely to hit Earth, and they have the ability to destroy a country, making these smaller bodies the top priority of planetary defense efforts.
But for ground telescopes, they are nothing more than a small spot of light that is difficult to detect, let alone study.
When one celestial body blocks another, their light will dim. By monitoring tiny fluctuations in light from Dimorphos and Didymos, NASA scientists can learn about information such as its rotational speed.
This will allow scientists to design an autonomous navigation system , guiding the "dart" to approach "prey" with the help of a new solar ion thruster.
But no one can tell what will happen next. "Suppose it is a solid rock, we have a solid spacecraft that is essentially playing a big billiard game in space... basically it can be solved as a simple physical equation." Cristina Thomas, a planetary scientist at Northern Arizona University , said that when the target is composed of thousands of rocks, it is much harder to predict the consequences of hitting it than predicting a solid boulder. If DART hits a fragile gravel pile target, the crater will form within a few hours, a process that could take months or even years to model.
Recently, DART deployed a bread machine-sized cube satellite that will use two optical cameras to record the collision process and its results.
At the same time, James Webb and Hubble Space Telescope and 4 ground observatory will take turns to monitor. If Dimorphos is a fragile pile of gravel, the telescope should be able to capture images of it within hours of impact.
In the case where an asteroid is really threatening the earth, the solution is to impact the asteroid body with enough force to make it turn, but at the same time it cannot be too fierce, causing it to launch small rock fragments to the earth.
DART mission will provide scientists with more data to improve their planetary defense plans.
