In Tuesday night, a $330 million spacecraft will crash into the asteroid Dimorphos. It is no coincidence that their nickname “Dart” is reminiscent of the small darts that are thrown at targets. The crash is fully deliberate. NASA launched the probe, which has the mass of a small car, into space specifically to crash it into Dimorphos at 23,800 kilometers per hour. A previously deployed miniprobe from Italy will film everything.
What should it? Well, one wants to see if such a collision is enough to change Dimorphos’ trajectory. Because the Brocken is 163 meters long. Asteroids of this caliber are the most dangerous in terms of a possible collision with Earth: they are large enough to cause a national catastrophe at the point of impact. At the same time, they are so small that we know far too few of them.
Almost 30,000 celestial bodies – mainly asteroids – are currently known to come close to Earth’s orbit or even cross it as they orbit the Sun. Two thirds of these are less than 140 meters and are therefore relatively uncritical. When they fall to the ground, they burn up in the atmosphere. Only the largest among them reach deeper air layers. However, they are not always completely harmless. A twenty-meter chunk that fell in Russia in 2013 only disintegrated at such a low level that it triggered a blast wave. It shattered windows in an entire region and injured more than a thousand people.
Nor should we be afraid of the really big cars at the moment. An asteroid with a caliber of ten kilometers, like the one that wiped out the dinosaurs and would at least mean the end of human civilization today, only hits the earth every hundred million years. And such a tumble on earth orbit is too big to escape the scientists. Such a catastrophe is therefore impossible within the next hundred years – however, it is not possible to predict asteroid trajectories further into the future with certainty. In the case of boulders with a diameter of one kilometer – one that would still destroy an entire continent – we are 98 percent sure that none will hit us in the next hundred years.
The problem, however, is asteroids between 140 and 1,000 meters – exactly those like Dimorphos. There are probably many more on a sure collision course with Earth without our knowledge. Their impact would still have the effect of a very large nuclear bomb. So if worst comes to worst, he can wipe out a major city.
What should we do if we suddenly discover one? If we are not very unlucky, it will still be several years to decades before the impact, and one can try to prevent the disaster. Because a small push is enough to change its trajectory so that it misses the ground. To do this, one could shoot at the asteroid with, for example, a laser or with bundled sunlight from a concave mirror placed in space. Or you detonate a nuclear bomb near its surface. However, the simplest thing would be a targeted crash, like what is being tried on Dimorphos now.
By the way, he is only a test object and is not a danger himself. It’s also impossible for “Dart” to accidentally kick him to the ground on Tuesday. Dimorphos is a small moon. Every 12 hours it orbits a slightly larger asteroid, and the crash will shorten this orbit by just 4.2 minutes – if the experiment works and “Dart” can transfer enough of its kinetic energy to the clump.