The fall to Earth of an asteroid is one of the basic scenarios of the Apocalypse used in science fiction. To prevent fantasies from becoming a reality, humanity has prepared in advance to protect itself from such a threat, and some methods of protection have already been worked out in practice. It is interesting that the approaches of scientists from the United States and the Russian Federation in this matter have their differences.
Today, March 8, 2016, at a distance of about 22,000 kilometers from the Earth (14,000 kilometers below the orbit of geostationary satellites), an asteroid 2013 TX68 with a diameter of 25 to 50 meters will pass. It has an erratic, poorly predictable orbit. Subsequently, it will come to Earth in 2017, and then - in 2046 and 2097. The probability that this asteroid will fall to Earth is vanishingly small, but if this happens, then the blast wave will be twice as powerful as that produced by the explosion of the Chelyabinsk meteorite in 2013.
So, 2013 TX68 does not pose a particular danger, but the asteroid threat to our planet is not limited to this relatively small "cobblestone". In 1998, the US Congress instructed NASA to detect all asteroids close to Earth and capable of threatening it as large as one kilometer across. According to NASA's classification, all small bodies, including comets, that approach the Sun at a distance equal to at least 1/3 of an astronomical unit (AU) fall into the “nearby” category. Recall that a.u. Is the distance from the Earth to the Sun, 150 million kilometers. In other words, so that the "visitor" does not cause concern among earthlings, the distance between him and the circumsolar orbit of our planet must be at least 50 million kilometers.
By 2008, NASA had generally complied with this mandate, finding 980 such flying debris. 95% of them had precise trajectories. None of these asteroids pose a threat for the foreseeable future. But at the same time, NASA, based on the results of observations obtained using the WISE space telescope, came to the conclusion that at least 4,700 asteroids with a size of at least 100 meters pass by our planet periodically. Scientists were able to find only 30% of them. And, alas, astronomers managed to find only 1% of the 40-meter asteroids periodically "walking" near the Earth.
In total, as scientists believe, up to 1 million asteroids close to the Earth "roam" in the Solar System, of which only 9600 were reliably discovered. If a "cobblestone" 100-150 meters in size passes at a distance of 0.05 AU. from our planet (which is about 20 Earth-Moon distances, that is, 7.5 million kilometers), it automatically falls into the category of "potentially dangerous objects" according to NASA's classification. The American Aerospace Agency currently has about 1,600 such units.
How great is the danger
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The probability of a large celestial "debris" falling to Earth is very small. It is believed that asteroids up to 30 meters across should burn up in dense layers of the atmosphere on their way to the planet's surface, or at least collapse into small fragments.
Of course, a lot will depend on the material from which the space tramp is "made". If it is a "snowball" (a cometary fragment, consisting of ice interspersed with stones, soil, iron), then even with a large mass and size, it is likely to "pop" like the Tunguska meteorite somewhere high in the air. But if a meteorite consists of stones, iron or an iron-stone mixture, then even with a smaller size and mass than the "snowball", it will have much more chances to reach the Earth.
As for the celestial bodies up to 50 meters across, they, as scientists believe, “visit” our planet no more than once every 700-800 years, and if we talk about 100-meter uninvited “guests”, then here the frequency of “visits” for 3000 years or more. However, the 100-meter fragment is guaranteed to sign a verdict for a metropolis like New York, Moscow or Tokyo. Debris from 1 kilometer in size (a guaranteed catastrophe of a regional scale, approaching a global one) and more falls to the Earth not more often than once every several million years, and even giants 5 kilometers or more in size - once every tens of millions of years.
Good news in this sense was reported by the Internet resource Universetoday.com. Scientists from universities in Hawaii and Helsinki, observing asteroids for a long time and assessing their number, came to an interesting and comforting conclusion for earthlings: celestial "debris" spending enough time near the Sun (at a distance of at least 10 solar diameters) will be destroyed by our luminary.
True, relatively recently, scientists started talking about the danger posed by the so-called "centaurs" - giant comets, the size of which reaches 100 kilometers across. They cross the orbits of Jupiter, Saturn, Uranus and Neptune, have extremely unpredictable trajectories and can be directed towards our planet by the gravitational field of one of these giant planets.
Forewarned is forearmed
Humanity already has technologies for protection from asteroid-cometary danger. But they will be effective only if the heavenly fragment threatening the Earth is detected in advance.
NASA has a "program for the search for objects located close to the Earth" (also called Spaceguard, which translates as "guardian of space"), which uses all the means of space surveillance at the disposal of the agency. And in 2013, the Indian PSLV launch vehicle launched into near-Earth polar orbit the first space telescope designed and built in Canada, whose task is to monitor outer space. It was named NEOSSat - Near-Earth Object Surveillance Satellite, which translates as "Satellite for tracking objects close to the Earth." It is expected that in 2016-2017 another space "eye", called Sentinel, created by the US-based non-governmental organization B612, will be launched into orbit.
Works in the field of space surveillance and Russia. Almost immediately after the fall of the Chelyabinsk meteorite in February 2013, employees of the Institute of Astronomy of the Russian Academy of Sciences proposed to create a "Russian system for countering space threats." This system would represent only a complex of means for observing outer space. Its declared value was 58 billion rubles.
And recently it became known that the Central Scientific Research Institute of Mechanical Engineering (TsNIIMash), within the framework of the new Federal Space Program, until 2025, plans to create a center for warning about space threats in terms of asteroid-cometary hazard. The concept of the "Nebosvod-S" complex involves placing two observation satellites in geostationary orbit and two more in the orbit of the Earth's revolution around the Sun.
According to TsNIIMash specialists, these devices can become a "space barrier" through which practically no dangerous asteroid with dimensions of several tens of meters will fly unnoticed. "This concept has no analogues and can become the most effective for detecting dangerous celestial bodies with a lead time of up to 30 days or more before they enter the Earth's atmosphere," the press service of TsNIIMash noted.
According to a representative of this service, the institute participated in 2012-2015 in the international project NEOShield. As part of the project, Russia was asked to develop a system for deflecting asteroids that could threaten the Earth using nuclear explosions in space. Cooperation between Russia and the United States was also outlined in this area. On September 16, 2013 in Vienna, Rosatom General Director Sergei Kiriyenko and US Energy Secretary Ernst Moniz signed an agreement between the Russian Federation and the United States on cooperation in scientific research and development in the nuclear and energy fields, which created the preconditions for interaction between specialists from the two countries in danger. Unfortunately, the sharp aggravation of Russian-American relations, which began in 2014, actually put an end to such interaction.
Push or detonate
The technology at the disposal of mankind provides two main ways of protecting against asteroids. The first can be used if the danger is detected in advance. The task is to direct a spacecraft (SC) to the celestial debris, which will be fixed on its surface, turn on the engines and take the "visitor" away from the trajectory leading to a collision with the Earth. Conceptually, this method has already been tested three times in practice.
In 2001, the American spacecraft "Shoemaker" landed on the asteroid Eros, and in 2005 the Japanese probe "Hayabusa" not only sank to the surface of the asteroid Itokawa, but also took samples of its substance, after which it returned safely to Earth in June 2010. The relay race was continued by the European spacecraft "Fila", which landed on comet 67R Churyumov-Gerasimenko in November 2014. Imagine now that instead of these spacecraft tugs would be sent to these celestial bodies, the purpose of which would not be to study these objects, but to change the trajectory of their movement. Then all they had to do was to get hold of an asteroid or comet and turn on their propulsion systems.
But what to do in a situation if a dangerous celestial body is discovered too late? There is only one way left - to blow it up. This method has also been tested in practice. In 2005, NASA successfully rammed Comet 9P / Tempel with the Penetrating Impact spacecraft to perform spectral analysis of cometary matter. Suppose now that instead of a ram, a nuclear warhead would be used. This is exactly what Russian scientists propose to do by striking the Apophis asteroid with modernized ICBMs, which is to approach Earth in 2036. By the way, in 2010 Roskosmos already planned to use Apophis as a testing ground for a spacecraft tug, which was supposed to take the “cobblestone” aside, but these plans remained unfulfilled.
There is, however, a circumstance that gives experts reason to show skepticism about the use of a nuclear charge to destroy an asteroid. This is the absence of such an important damaging factor of a nuclear explosion as an air wave, which will significantly reduce the effectiveness of using an atomic mine against an asteroid / comet.
To prevent the nuclear charge from losing its destructive power, experts decided to use a double strike. The hit will be the Hypervelocity Asteroid Intercept Vehicle (HAIV) currently under development at NASA. And this spacecraft will do it in the following way: first, it will enter the “home stretch” leading to the asteroid. After that, something like a ram will separate from the main spacecraft, which will strike the asteroid the first blow. A crater is formed on the "cobblestone", into which the main spacecraft with a nuclear charge will "screech". Thus, thanks to the crater, the explosion will occur not on the surface, but already inside the asteroid. Calculations show that a 300-kiloton bomb, detonated only at a depth of three meters under the surface of a solid body, increases its destructive power by at least 20 times, thus becominginto a 6-megaton nuclear charge.
NASA has already awarded grants to several US universities to develop a prototype of such an "interceptor".
The main American "guru" in the fight against the asteroid hazard with nuclear warheads is the physicist and nuclear weapons developer at Livermore National Laboratory, David Dearborn. He is currently working with his colleagues on high alert for the W-87 warhead. Its capacity is 375 kilotons. That's about one third of the power of the most destructive warhead currently in service in the United States, but 29 times more powerful than the bomb that fell on Hiroshima.
Rehearsal for destruction
The destruction rehearsal will be conducted by the European Space Agency (ESA). Asteroid 65802 Didyme, discovered back in 1996, was chosen as the "victim". It is a binary asteroid. The diameter of the main body is 800 meters, and the diameter of the one that revolves around it at a distance of 1 kilometer is 150 meters. Actually, Didyme is a very "peaceful" asteroid in the sense that no threat to Earth comes from it in the foreseeable future. Nevertheless, ESA, together with NASA, intends to ram it with a spacecraft in 2022, when it is 11 million kilometers from Earth.
The planned mission received the romantic name AIDA. True, she has nothing to do with the Italian composer Giuseppe Verdi, who wrote the opera of the same name. AIDA is an abbreviation for Asteroid Impact & Deflection Assessment, which translates as "Assessment of the collision with an asteroid and the subsequent change in its trajectory." And the spacecraft itself, which is to ram the asteroid, was named DART. In English, this word means "dart", but, as in the case of AIDA, this word is an abbreviation of the phrase Double Asteroid Redirection Test, or "Experiment to change the direction of motion of a double asteroid." "Dart" must crash into Didim at a speed of 22,530 kilometers per hour.
The consequences of the impact will be observed by another apparatus flying in parallel. It was called AIM, that is, "target", but, as in the first two cases, it is an abbreviation: AIM - Asteroid Impact Monitor ("Tracking collision with an asteroid"). The purpose of the observation is not only to assess the impact of the impact on the asteroid's trajectory, but also to analyze the knocked-out asteroid matter in the spectral range.
But where to place the asteroid interceptors - on the surface of our planet or in near-earth orbit? In orbit, they are in “readiness number one” to repel threats from space. This eliminates the risk that is always present when launching a spacecraft into space. Indeed, it is at the stage of launch and withdrawal that the probability of failure is highest. Imagine: we urgently need to send an interceptor to an asteroid, but the launch vehicle could not take it out of the atmosphere. And the asteroid is flying …
However, none other than Edward Teller himself, the "father" of the American hydrogen bomb, opposed the orbital deployment of nuclear interceptors. In his opinion, one cannot simply bring nuclear explosive devices into near-earth space and calmly watch them revolve around the Earth. They will need to be constantly maintained, which will take time and money.
International treaties also create involuntary obstacles to the creation of nuclear asteroid interceptors. One of them is the 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space and Under Water. The other is the 1967 Outer Space Treaty, which prohibits the introduction of nuclear weapons into space. But if people have a technological "shield" that can save them from the asteroid-cometary apocalypse, then it would be extremely unreasonable to put political and diplomatic documents into their hands instead.