Imagine that one day the Observatory as one of the world confirmed that the Earth is approaching asteroid, a collision is imminent. The space of the nation must agree on how to stop him. Chunks of stone flying through space, can cause catastrophic damage to our planet. What happens next depends on how much time for reflection we leave the asteroid. None of the options will not be easy, may need the use of nuclear weapons. What are we going to do when this day will come?
Large asteroids falling rarely. The last of these that caused severe damage to life, was the Tunguska meteorite in 1908. It is believed that it was a meteorite that exploded 10 miles above the remote Siberian region.
This kind of drop happens once in several centuries. But Siberia far; even today its population is small and scattered over a vast territory. If the same object has arrived four or five hours later, he would fall to Saint Petersburg and produced an explosion that is equivalent megaton nuclear explosion.
A smaller version of this nightmare scenario, we had the privilege of watching recently. In 2013 the Chelyabinsk meteorite that disintegrated at an altitude of 30 miles, blew out Windows and injured 1400 people in the Russian city. An explosion that he caused, was equivalent to 500 kilotons — about 30 bombs dropped on Hiroshima — but it was high enough that everything worked. Those crashes happen quite often, three times a year on average. Most of them occur over the ocean or in remote locations, so they don’t notice. And still pressing question is whether there will be such a drop in General and when will that happen?”.
States treat this issue very seriously and have taken the first steps to prevent dangerous falls. In January, NASA has formed a Department for the coordination of planetary defense (Planetary Defense Coordination Office), which will become the focal point for the observation of asteroids and other space agencies over how to proceed in case of a possible collision of large space rocks with the Ground.
At the moment PDCO spends most of its efforts on detection, coordination of the various surveillance programs, says Lindley Johnson, the officer of the planetary defense NASA. Because it is impossible to deal with space rocks, if you do not know where they are. “We’re trying to find all that may become a threat in the coming years and even decades in advance,” he says. Once an asteroid threat is detected, work has begun on plans to halt this particular object.
The simplest method involves a kind of planetary Billiards that uses space probe, which would send a heavy object (or the probe itself) for collision with the object. Then the asteroid is believed to change course and fly past the Earth.
The joint mission of the European space Agency and NASA will test the technology in the next few years: it is called Asterod Assesment of Impact and Deflection (Aida). The mission consists of two spacecraft, one of which is called the Asteroid Impact Mission (Aim), which will be launched in late 2020, and the second, the Double Asteroid Redirection Test (Dart), to be launched in 2021.
In 2022 they will arrive on the double asteroid 65803 Didymos, which is flying with a companion Didymoon. Didymos in diameter of 780 meters, and Didymoon – 170 meters. Junior senior goes around every 11.9 hours, and they are close to each other — just 1100 metres. Camera Aim will meet with the asteroid and study its composition. As soon as I get the Dart, it hits the Didymoon, and Aim will examine the consequences for the orbit of younger rocks. The objective of the mission is to find out how you can redirect the asteroid so as not to take him on a dangerous trajectory. With this, in fact, you should start planning the mission.
To understand the prospect of such a mission, the famous Arizona crater in the U.S. state of Arizona was probably formed by the object three times less than Didymoon, and its diameter is 1.18 km. A stone the size of a Didymos, which hits the Earth at a speed of 125 feet per second, will cause an explosion equivalent to two megatons; enough to destroy a city. And this is the minimum speed. At its maximum speed (about 186 meters per second) he threw four megatons of energy — about four million tons of TNT.
“We want to change the orbit of this satellite,” says Patrick Michel, senior researcher at the National research center of France and one of the team leaders Aida, since the orbital speed of the satellite around the main body only 19 cm per second”. Even small changes can be measured from the Ground, he adds, changing the orbital period Didymoon four minutes.
It is also important to see if it works the explosive element. “All models of the collisions that we are considering based on the understanding of the physics of the collision, which was tested only on a laboratory scale in centimeter order,” says Michelle. Whether these will work on models of real asteroids, it is not entirely clear.
Johnson adds that this technology is the most Mature — people have already demonstrated the ability to get to the asteroid, in particular, with the Dawn mission to Ceres and the mission “Rosetta” to the comet 67P/Churyumov — Gerasimenko.
In addition to the approach with the warhead, there is also a gravity approach is simply to place a relatively massive spacecraft in orbit near the asteroid and give their mutual gravitational attraction will gently guide the object onto a new path. The advantage of this method is that essentially only need to deliver to the destination spacecraft. The NASA ARM mission may indirectly test this idea; part of that plan is the return of the asteroid in near-earth space.
However, a key element of such methods is time; will need a good four years to build the space mission beyond Earth’s orbit, and the spacecraft will need an extra year or two to get to the right asteroid. If time is not enough, have to try something else.
Quichen Zhang, a physicist at the University of California at Santa Barbara, believes that we will help lasers. The laser does not blow up the asteroid, like some kind of Death Star, but will vaporize a small part of its surface. Zhang together with his colleagues he worked with an experimental cosmologist Philip Lubimym to represent a set of orbital simulations of the Astronomical society of the Pacific ocean.
Such a plan might seem inefficient, but remember that if you start early and work long, you can change the course of the body for thousands of kilometers. Zhang said that the advantage of laser is that big laser it is possible to build in earth orbit and will not need to fly to the asteroid. The laser power of one gigawatt, running for months, can shift the 80-meter asteroid — such as the Tunguska meteorite — two of the earth’s radius (12 800 km). This is enough to avoid a collision.
Another variant of this idea is to send a spacecraft equipped with less powerful laser, but in this case he will have to get to the asteroid and follow him relatively close. Since the laser will be smaller — in the range of 20 kW — he will have to work for many years, although the simulation of Zhang shows that the satellite, which is pursuing the asteroid to push it off course over 15 years.
Zhang said that among the advantages of using the Earth’s orbit that the prosecution of an asteroid or comet is not so easy to implement as it seems, despite the fact that we already do. “Rosetta was originally supposed to fly to another comet (46P), but the delay in launch has meant that the original purpose has gone with eye-catching position. But if the comet decides to go to Earth, we will not be able to change it to a better option”. To monitor the asteroid is easy, but to reach it, you still need at least three years.
Johnson, however, notes one of the biggest problems associated with the use of laser of any kind: no one has launched a one-kilometer object in orbit, not to mention the laser or the whole array itself. “There are a lot of immature moments in this plan; it’s not even clear how to reliably convert solar energy into a laser that functioned long enough.”
There is a “nuclear option”. If you have seen the movie “Armageddon”, this option seems simple, but in reality it is much harder than it looks. “We’ll have to send the whole infrastructure,” said Massimiliano Vasile of the University of Strathclyde. He offers to blow up a nuclear bomb at some distance from the goal. As with the laser, the plan is to evaporate part of the surface, thereby creating traction and changing the orbit of an asteroid. “When you undermine, you get the advantage of high efficiency of energy use,” he says.
While lasers and nuclear bombs can work when the asteroid is closer, even in these cases it would be important to have the composition of the object, since the evaporation temperature will vary from asteroid to asteroid. Another question — the flying rubble. Many asteroids can be just a collection of rocks that are weak stick together. In the case that the warhead will not work. Gravitational tug is better — it does not depend on the composition of the asteroid.
Any of these methods, however, can encounter the last obstacle: politics. The outer space Treaty of 1967 prohibits the use of nuclear weapons and their testing in space, and the output gigawatt laser in orbit can make some people nervous.
Zhang said that if the power of the orbital laser will be reduced to 0.7 GW, it will shift the asteroid by only 0.3 of the radius of the earth — circa 1911 kilometers. “Small asteroids that could destroy a city, is much more widespread than the destroyers of planets. Now imagine that such an asteroid on a trajectory that leads to new York. Depending on the circumstances, the attempt partially failed and the deviation of the asteroid from the Earth can shift the place of falling on London, for example. If there is at least some risk of error, the Europeans simply will not allow US to reject the asteroid.
Such obstacles generally expect at the last moment. “In these treaties there is a loophole,” Johnson said, speaking of the outer space Treaty and the agreement on a total ban on nuclear testing. They do not forbid launches of ballistic missiles, which move through space and can be armed with nuclear weapons. And in light of the need to protect the planet, critics and patience.
Michelle also notes that, unlike any other natural disaster, specifically that we can avoid. “The natural risk of such is very low, compared to the tsunamis and the like. But in this case we can do something”.
What can you do to save the Earth from a deadly asteroid?
Ilya Hel