Scientists have calculated the consequences of the explosion of an asteroid with a nuclear charge
The new study, conducted by scientists at Johns Hopkins University and Lawrence Livermore National Laboratory, not only simulates the destruction of an asteroid threatening the Earth by a nuclear warhead, but also examines in detail how different asteroid orbits and different velocity distributions of the resulting fragments affect their further expansion. Earlier, there were concerns that the destruction of the asteroid would lead to a swarm of equally dangerous debris. Now it turns out that all this is not so critical. An article about this was published in the journal Acta Astronautica.
If it is established that a dangerous asteroid is on the trajectory of a collision with the Earth, then it is most logical to start deflecting it from this trajectory in advance, gradually nudging it with small impulses, while achieving relatively small changes in speed.
This tactic will allow you to keep the heavenly body in relative integrity, so as not to deal separately with each piece that has flown away from it. Gradual deflection can be achieved with rocket motors attached to the asteroid, kinetic strikers, or a series of small explosions.
However, if a dangerous asteroid was discovered too late to be rejected in advance, another option remains – to transfer to the asteroid a large enough amount of energy one-time in order to break it into many fragments well dispersed in space. This approach is called undermining, and people often think of this option when they imagine a planetary defense against dangerous objects. And although scientists would prefer to have more time to prevent the consequences of an asteroid fall, they must be prepared for any scenario, since so far many near-Earth asteroids remain undiscovered.
As an example, it was assumed that a nuclear bomb with a capacity of one megaton would detonate a few meters from the surface of an asteroid 100 m in diameter.This is about a fifth of the actual near-Earth asteroid Bennu, discovered in 1999.
The results presented in the article are encouraging: for all five considered orbits, the detonation of a dangerous object just two months before its collision with the Earth will reduce the mass of debris colliding with the planet by at least a thousand times – that is, 99.9% of the mass of debris simply does not fall into the Earth's atmosphere.
For a larger asteroid, the results will no longer be as reliable, but even so, the mass of debris could be reduced by 99% if the destruction of the asteroid occurs at least six months before its collision with Earth.
“One of the challenges in assessing the destruction of an asteroid is that we need to simulate the orbits of all of its fragments, which is usually much more difficult than simulating a simple deflection of an object,” explains lead author Patrick King of the Applied Physics Laboratory at Johns Hopkins University in Maryland. “Nevertheless, we need to try to solve these problems if we are to evaluate the method of disruption as a possible strategy for the future.”
The main conclusion of the study, according to King, was that the use of a nuclear charge can be considered a very effective method of protection in the most extreme case:
“We focused on studying precisely the late cases of the destruction of the asteroid, when it disintegrates shortly before the collision with the Earth. If you have enough time, say a decade, then it is preferable to use kinetic impact elements to gradually deflect the dangerous asteroid. “
Kinetic impactors have many advantages: first, the technique is well known and is now being tested in real space missions such as DART. It allows you to deal with a wide range of possible threats, if you have enough time. However, this method also has some limitations, so it is important that in the event of an emergency, as many options as possible to deal with the threat are available, including ways to cope with an asteroid discovered at the latest stages.
A program called Spheral, which was used to simulate the destruction of asteroids by nuclear charges, was written by one of the co-authors of the article, Michael Owen. It allows you to study the process of destruction of a stone asteroid and track the fate of the resulting fragments. The team used Spheral to track the evolution of the debris cloud, taking into account both their influence on each other and the gravitational influence from the Sun and other planets.
“If we spot a dangerous object too late to safely deflect it, then our best remaining option is to destroy it completely, and as carefully as possible so that the resulting fragments would almost never hit the Earth,” says Owen. – This is not so easy to achieve: if you break an asteroid into pieces, then the resulting cloud of debris will follow its own path around the Sun, interacting gravitationally with each other and with other planets. This cloud will tend to stretch into a curved stream of fragments around the original path along which the asteroid moved. How quickly these pieces fly apart (combined with how long it will take before the cloud crosses the path of the Earth) will determine how much debris falls to the Earth. “
Meanwhile, NASA and other space agencies continue to develop their planetary defense systems, especially when it comes to detecting potentially dangerous asteroids earlier. After all, detecting a killer asteroid in advance can be truly critical to maximizing our chances of knocking that asteroid off course.
The fact that the danger of falling of such objects is quite real and that such events, even in the era of total monitoring of the surrounding outer space, can happen suddenly, is evidenced by photographs and videos of bright large fireballs that fall into the lenses of DVRs. On February 15, 2013, in the Chelyabinsk region, a 20-meter fragment weighing 13 thousand tons led to real destruction and injuries among the population over a very large territory. Then over a thousand people were injured, windows were broken in many buildings, and the blast wave circled the entire Earth twice. After some time, fragments of a meteorite with a total mass of almost a ton were removed from Lake Chebarkul.
But asteroids up to 100 m in size carry only local destruction and do not threaten with global catastrophes. A much greater danger is carried by asteroids of a kilometer size, which, even when they hit the oceans, can generate destructive tsunamis on the coast, and when they hit the fractures of lithospheric plates, they can provoke earthquakes.
The greatest danger to all life on the planet is represented by ten-kilometer and larger asteroids. The most famous ancient impact crater with a diameter of about 180 km in the Yucatan Peninsula was formed by just such an asteroid, which is believed to have led to the death of dinosaurs 65 million years ago. The consequence of the fall of such an asteroid is the release of energy millions of times higher than the energy of the explosions of the most powerful thermonuclear bombs. This causes tsunamis, fires around the world, ash and carbon monoxide emissions, which cover the planet's surface from direct sunlight for many years. The sulfur released from the disaster can lead to the abundant formation of clouds of sulfuric acid, which then pour out in acid rain.
