by Acad. Lev ZELENY, director of the RAS Institute of Space Research; Viktor YESIN, Colonel-General, rtd, former, head of the chief Staff of Strategic Rocket Forces, Professor of the Department of World Politics, Lomonosov Moscow State University; Acad. Andrei KOKOSHIN, Dean of the World Politics Department, Lomonosov Moscow State University

A great meteorite exploded on the 15th of February 2013 over Chelyabinsk, making a thousand people wounded and their homes damaged, with windows smashed and all that. The mass of this fireball is estimated at 7 to 10 thousand tons. It means that asteroids, or tiny planets, pose a real threat. A larger cosmic body may cause even greater destruction should it hit urban areas and, in a worst-case scenario, threaten the very existence of the human race.

Over these last twenty or twenty-five years we have collected a large body of evidence on asteroids (planetoids, minor planets) thanks to vigorous ground and space studies. Many astrophysicists conclude that one such space body may plunge to earth in a violent explosion someday. The threat is quite real.

The available knowledge and technologies are not sufficient yet so as to predict this threat and react accordingly. We are still unable to collate it with other global dangers. We need far more data for detecting small cosmic objects and making early warnings.

There is a large class of asteroids and other celestial bodies crossing the earth's path and/or approaching it. Given certain conditions, they may hit our planet and inflict grave damage. True, this is only a possibility of collision: asteroids revolve in stationary orbits way out of the earth's path and thus cannot collide with the globe. And yet there are planetoids that may approach it to a distance equal to several radii of the lunar orbit and get even closer. A gravitational pull of the earth and/or the moon may cause an asteroid to change its orbit and thus increase the probability of a collision which is hard to foretell.

The size of a celestial body is likewise important in the event of a collision. The smallest asteroid posing a global menace is 50 to 100 meters across. The energy released in a collision with a body like that is comparable to the blast of a powerful hydrogen bomb. The probability of such small objects crashing on earth is one in hundreds and dozens of thousands of years, depending on their dimensions. Asteroids measuring hundreds of meters across--a kilometer or so--are the greatest danger. A planetoid like that may hit the earth but once in several hundreds of thousands of years. If an asteroid with a diameter of about 10 km plunges to earth, well, it may wipe out human civilization. Fortunately there is a slim chance of a like calamity: there remain but few such planetoids in orbit since our planet came into being billions of years ago.

Today there are several foreign programs for spotting asteroids coming closer to the earth. Such programs make use of data collected by ground and orbital stations (systematic observations were launched in the mid-1990s). To date as many as 10,000 objects have been registered classed as bodies approaching the earth (http://neo.jpl.nasa.gov./stats/). As shown by detection statistics, the number of asteroids around a kilometer across has been increasing but slowly, their overall number is close to 900; their growth dynamics is close to the saturation point. The number of newly discovered asteroids in the 300 m to 1 km range is about 3,000, and this number is close to the saturation point, too. Yet it is hard to spot smaller planetoids measuring dozens of meters across, for they defy detection by the available optical facilities. For instance, asteroid 2012 DAK (~40 m across) that flew in on February 15, 2013, had been discovered only a year before. As many as 3,000 celestial bodies like that had been catalogued so far. Obviously, the number of thus identified bodies will be on the rise with the progress of observation facilities. The total number of decameter (i.e. in the 10 to 100 m range) asteroids is estimated at 100,000.

Asteroid Apophys (2004-MN4) detected in 2004 is of particular interest as a possible threat, for its orbit crosses into the terrestrial path. However, at the earth's perihelion (the point in the orbit of a planet or other heavenly body at which it is closest to the sun) it may approach to a critical distance. In 2029 it will fly by at a distance of 37-38 thousand kilometers from the center of our planet, that is it will be in the region of orbits of geostationary satellites. Radar observations show that Apophys will not collide with the earth, though due to certain inaccuracies in the initial data there is still a negligeable probability (~10^-5-10^-6) that this cosmic wanderer could hit the globe in 2036, and it is most unlikely it would do that in subsequent years. The latest data on Apophys were collected at the Herschel space observatory of the European

Space Agency; this asteroid measures 325+15 m in diameter. The energy that will be released should it smash into the earth is estimated at 500 megatons of the TNT equivalent or so. But the Tunguska meteorite that crashed into earth in eastern Siberia more than a hundred years ago is thought to have liberated energy equal to as much as 10 to 40 megatons. Such parameters as the angle of incidence, mass and structure of an asteroid are also important, and so is the place where it explodes. That explosion, though devastating a territory thousand of square kilometers large, would hardly entail long-term global aftereffects like an "asteroid winter".

It is not enough to watch the movements of potentially dangerous asteroids. We should look into their physical characteristics like mass, density and composition that may induce orbital changes. Such data are significant both from a practical (defense against asteroids) and from a theoretical standpoint: minor heavenly bodies of the solar system like asteroids and comets not modified by endogenic activities are the primary "building blocks" that went into the making of planets and their satellites. So research into the physicochemical characteristics of planetoids could help to unravel the mystery implicated in the formation and evolution of the family of solar

Jarkowski effect: 1--thermal radiation of an asteroid; 2--its revolution; 2.1--its sun-lit surface at daytime; 3--its orbit; 4--thermal radiation of the sun.

planets. Then we shall learn why Venus, Earth and Mars, so much alike originally, have followed different evolutionary paths. We shall learn whether our planet is going to become like a burning hot Venus with its overly dense atmosphere or a cold Mars with its very thin atmosphere. Addressing such problems, basic science is ultimately seeking safe ways of the earth's evolution.

We in this country are out to build a space vehicle for studying the near-earth asteroid and making high-precision measurements of its parameters. We are planning to

send a radio beacon onto its surface that will for as long as ten years monitor the asteroid's orbital parameters and their perturbations and disturbances. Data collected in that mission may be helpful in predicting the time of a possible collision with the earth and taking preemptive steps.

Depending on the orbital parameters and characteristics of this planetoid we might try to act upon it and get it to change its trajectory. Say, a large missile could be sent to attack the asteroid; or it may be acted upon by a weak force for a long time, for instance, one generated by the low-thrust engine of a space vehicle sitting on the surface of the asteroid. Of late it has been suggested to make use of what is known as the Jarkowski effect when a revolving asteroid emits a weak propulsion thrust on account of thermal radiation of its surface heating in the daytime and cooling at night. This thrust imparts an additional propulsion causing gradual changes in the orbital parameters. The magnitude and the direction of the propulsion thrust depend on the velocity of the revolution, structure and physical parameters of the asteroid. An increase in the natural propulsion force could occur if the surface temperatures of the asteroid are changed so that in decades its orbit will move off farther from the earth. Other practical remedies are proposed to ward off the threat, but they still look too far-fetched.

There is yet another intriguing possibility--to make use of the inherent potential of asteroids. For example, the 2012DA14 asteroid about 130,000 tons large contains about 5 percent of water that can be utilized as rocket fuel for interplanetary spacecraft. Since 10 percent of its mass is supposedly made up of iron, nickel and other metals common to asteroids, it as well as other planetoids is a possible mine of extraterrestrial useful minerals. Deep Space Industries (DSI) of the United States assesses the cost of the asteroid's mineral wealth at 195 bin dollars, though at this stage mineral mining out there is not expedient yet economically, a DSI report says.

It is high time that policy-makers and statesmen should join scientists in warding off the threat. The international community should pool efforts toward this end, above all industrial nations relying on advanced know-how and technologies. Such countries as Russia, the United States, China, the European Union countries and in part India do have such technologies. This cooperation will involve huge outlays in money, research and organizationally.

This is a live issue to be considered by Russia and other nations on a bilateral and multilateral basis, including UN member nations, for a planetary body may imperil global civilization. Permanent members of the UN Security Council should take the initiative. To begin with, the UN Committee on the Peaceful Uses of Outer Space should set up a special subcommittee to coordinate efforts of UN member states in building up a system of planetary defenses.

If established, this subcommittee could set up an international center concerned with a monitoring of planetary dangers and preventive measures.

Today some countries have at their disposal detection and interception facilities targeted at other objectives, though it must be rather difficult to reorient them to assignments related to the cosmic danger. A new global early detection and warning system should be built on the basis of the available technologies used in outer space both for civilian and for military purposes, say, in space monitoring and anti-missile defenses.

Space facilities for early detection are to play a major part--specifically, those in a geostationary orbit working at the same azimuths as menacing asteroid. Scientists and policy-makers ought to get down to a special-purpose space project in averting the possible threat. We in this country have done some spadework which should be evaluated and brought together. This work should rely on adequate financial support and high-level government guidance.

It is very important to build an adequate system of space monitoring, tracking and information management and afterwards, at a later stage, deploy a system of on-line control over space interception facilities.

Effective interception facilities are a more difficult job than those of detection, tracking and early warning. In many respects it is more laborious than efficient antimissile defenses. This job should involve several echelons of interception, both at distant approaches to the earth and near its surface.

A system of interception of natural space objects based on available nuclear technologies appears most realistic at the present stage. Nonnuclear methods are likewise possible, but they are a thing of the distant future.

Now what concerns using thermonuclear charges in raw space. Any nuclear explosion is characterized by such deadly factors as Shockwave, light (thermal) radiation, penetrating radiation, electromagnetic impulse and radiation contamination (fall-out). In the absence of an atmosphere in outer space the Shockwave does not "work" as a destruction factor, while penetrating radiation, electromagnetic impulse and radioactive pollution are not capable of exerting any significant effect on an asteroid or a comet's nucleus and thus cannot dislodge a large mass of substances and produce an orbit-changing propulsion; high-precision interception is needed for that (direct hit of a nuclear-capable missile into the core of an asteroid or nucleus of a comet).

Ground-based interceptor missiles to be targeted at cosmic invaders should be powerful enough--say, like the booster rocket Saturn-5 built for the US lunar program or the Soviet H-1 carrier rocket meant for the same purpose. Space platforms for interceptor rockets--piloted or drones--are still another option. The mass and dimensions of interceptor rockets placed on outer space platforms should be far smaller than those on ground-based launchers. Yet such projects will involve great expenses in creating platforms like that, and in their putting into orbit with interceptor rockets on board.

High-yield nuclear charges, if mounted on ground-based interceptors, are also capable of getting asteroids and comets to change their orbits. One can draw upon our country's experience in building special-purpose nuclear charges that went to equip antimissiles of the A-135 missile-defense system deployed at Moscow. No other country, USA including, has a system like this.

It would be in place to recall at this point that Yuri Trutnev, one of the masterminds who created a super nuclear charge exploded in 1962 over Novaya Zemlya, is still active at the Sarov nuclear center.

A planetary defense system will involve many extraordinary problems--scientific and technological, organizational, political, and legal, which will have to be solved this way or that. Global security will be the acid test for humanity and its ability to ensure conditions for the prosperity of our civilization for hundreds of millions of years ahead...

In fact, collisions with asteroids and comets that we perceive as a global threat are actually part and parcel of the life of our planet and the solar system at large. Planets, the earth among them, took body and form through collisions of small fragments of protomatter billions of years ago. Comets must have brought in the water now filling our seas and oceans. For that matter one popular theory on the origin of life on earth contends that comets brought in "spores of life". And last, a collision with a giant asteroid about 65 mln years ago killed dinosaurs but made it possible for smaller animals, human ancestors including, the progenitors of Homo sapiens preoccupied now with the danger of asteroids and comets, to emerge on the arena.

... At civil defense lessons Soviet schoolchildren were taught quite a few useful things. They received certain essential tips-off in the event of a nuclear explosion: on seeing a dazzling nuclear flash, they had to take a white sheet, wrap themselves in, lie down on the floor and crawl away from the window, quickly.

In Chelyabinsk people wounded by glass splinters had a minute to do simple things like that. But they did not, and had to take the consequences. The older generation has forgotten such lessons taught at Soviet schools, and the younger set couldn't care less for lack of knowledge about what a nuclear strike is all about. Curiosity killed a cat, as the saying goes. And so the curious bunch glued to the windows to enjoy the natural show outside, a bright shooting star, a bolide. But the fall of a heavenly body is akin to a nuclear blast. It wouldn't be bad at all if our school kids were taught what they had to do on seeing a fireball. You've got to learn things. Not the hard way after you were warned.