Over the recent decades scientists have time and again discussed the probability of earth's collision with an asteroid or a comet ^* resulting in a global catastrophe capable of wiping off humankind or throwing it back into the stone age. Is there a way to ward off such menace? A year ago specialists of a number of scientific and production organizations of Russia rallied to found the Planetary Defense Center.

According to A. V. Zaitsev, Director General of the Center, a system capable of protecting earth against the threat of cosmic bodies is already designed and is termed the CITADEL . It provides for the creation of an online ground/space service of monitoring hazardous extraterrestrial objects.

Within its framework several specially equipped space launchers will permanently be on alert-scouts and interceptors. In case of emergency the former will head for the threatening cosmic body and, passing it at a hair's breadth, make update on its shape, size, mass, composition and trajectory. On the basis of the obtained information the next echelon of launchers, interceptors will be loaded with nuclear charges or other powerful means of repelling the object closing in on earth. Their key objective is to make the space wanderer so change its flight parameters, that it will pass us by.

A. V. Zaitsev believes that the CITADEL can be created within the forthcoming 5 to 7 years on the basis of the existing, primarily, military technology. The rather stringent requirements to means of hot interception are met by boosters DNEPR, ZENIT and PROTON . For example, ZENIT , along with a considerable payload capacity (up to 12 t), has unique pad-stay time characteristics which permit take-off within just an hour and a half following installation. MARS-96 (PHOBOS) and the PHOBOS-GRUNT module developed by Lavochkin NPO, as well as some of their foreign counterparts, may be used as basic space vehicles.

It is intended that initially the intercept technologies will be earth-based. Later they maybe deployed on orbital stations or even on the Moon.

Such system is expected to ensure reconnaissance and interception of small asteroids (up to a few hundred meters in diameter) within 1 million kilometers from our planet. To detect dangerous aliens more than 1 km in size, a remote interception service is designed with tasks much more com-

^* See: A. Mikisha, M. Smirnov, "Menace From Space: Can it Be Averted", Science in Russia, No. 4, 2001; A. Litvak et al., "Cosmic Wanderers", Science in Russia, No. 2, 2003. - Ed.

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plex than that, but then it will have advance time to prepare for them. After all, the system will have to launch substantial payloads to assemble in the earth orbit heavy interceptors with multi-stage booster blocks.

So, how much will the CITADEL cost? Mr. Zaitsev's answer is: "According to preliminary estimates, the volume of annual financing of the planetary defense project in the phase of development and engineering will make up from tens to hundreds millions of dollars, or less than 10 cents of annual insurance premium from each earthling. Therefore, a possible option of project financing may be creating a Humankind Insurance Fund".

To be true, even a project of such magnitude presently seeming fantastic, will not be able to secure earth from colliding with an asteroid tens or more kilometers in diameter. However, for this occasion the Center has a salvation option called PHOENIX whereby Moon will sustain an international base, "a Noah's ark- 2", for a small colony of humankind's representatives. After the global holocaust, having sat out the subsequent catastrophic events like "nuclear winter", they will be able to return to the renewed native planet...

Speaking about biblical parallels, this is how the "Revelation of St. John the Divine" describes the end of the world:

"And the third angel sounded, and there fell a great star from heaven, burning as it were a lamp, and it fell upon the third part of the rivers, and upon the fountains of waters...

And the fifth angel sounded, and I saw a star fall from heaven unto the earth, and to him was given the key of the bottomless pit."

Remarkably, something like that was observed in 1994 when the Shoemakers-Levi comet collided with Jupiter, splitting into a few luciferous pieces. Another example: 30 years ago some astronomers propounded that planetoid Icarus might not just come quite close to earth but crash into it replicating the fate of its mythological prototype. Luckily, more accurate computations failed to corroborate this apocalyptic forecast. A somewhat similar grim outlook was shaping up as regards another space visitor, the Halley Comet, but like Icarus it could scare only poorly informed people. Generally speaking, astronomers do not expect a fall on earth in the near future of any massive meteorite, not to mention an asteroid or a comet.

However, the situation is not quite as simple as that. Presently, asteroid watch is financed in the USA and Japan only. In the Southern Hemisphere it is not conducted at all. For that reason in June 2002 one such alien was spotted only after it had passed rushing in menacing proximity to us. What if it had not missed? We can only wonder.

But suppose, astronomers know exactly that we are being fast approached by a big heavenly body able to wipe any living creature off a continent or even render the biosphere incapable of sustaining higher life forms. How would billions of people react to such news?

Is it better if nobody knows about the imminent threat in advance? The affirmative answer is on the tip of tongue but with one reservation: not if mankind has a way to avert the global disaster. But there is a way, as evidenced by the CITADEL defense system.

When asteroid 2002 NT7 was first discovered on 9 July 2002, according

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to the initial calculations, it was to collide with earth on 1 February 2019. So, here is the date of the Final Judgement! But, as it had repeatedly been before, the prophecy was not corroborated. The trajectory update has proven that the cosmic body should not touch our planet, although it will pass close (I would like to believe). However, according to projections, that may only delay the tragic finale of civilization: three decades later the ferrocious 2002 NT7 will rush headlong to the earth again and may just as well crash into it in February 2060...

An original scheme of salvaging humankind from such a plague was proposed 10 years back by American astronomer H. Melosh and Russian geophysicist I.V. Nemchinov: to turn the asteroid into a sailboat! Naturally, the solar wind will be used as the propellant. An automatic vehicle will have to be sent to the dangerous heavenly body to install a "solar sail", an enormous convex screen of thin film. Solar rays will start to focus on a small area of asteroid surface evaporating the overheated matter. A jet stream like that of a rocket engine will tug the asteroid to a new orbit.

There are other ways of attaining a similar result. For example, to explode powerful nuclear charges in the direct vicinity of an asteroid. But how high is the probability of a cosmic disaster? To find it out, scientists study the so-called astroblemes - calderas left by falling on the earth of medium - sized heavenly bodies (craters left by small ones are quickly wiped off by natural phenomena). The quantity of discovered astroblemes is constantly rising, some of them reaching dozens of kilometers in radius. The size record is kept by the Nastopoca crater in the Hudson Bay - 440 km across, - but the Arizona crater, 180 m deep and 1.3 km in diameter, is the most famous and picturesque.

We have information that among the multitude of small meteorites, roughly once a month a large one of 0.5 t in weight enters the atmosphere, while 30 year statistics register one weighing up to 50 t. Should they cause any damage, not to mention kill people, we would know. In accordance with theoretical estimates, in average, once in 100,000 years our planet sustains a blow of a cosmic body with the mass of the order of 50,000 t.

A global disaster may be caused by the fall of an asteroid weighing hundreds of thousands of tons. Such remarkable phenomenon takes place roughly once in 20 to 60 million years. Some scientists propound that it is such a planetary cataclysm that caused the massive annihilation of dinosaurs. However, paleontological data prove that the process that had led to the extinction of dinosaurs took at least 20 million years, and the causes of the tragic end of the giant reptiles were mainly ecological (that does not rule out other hypotheses) ^* .

Generally, up till now we have no reliable data of a murderous impact upon terrestrial life of a monstrous cosmic blow during at least the recent half-a-billion years. That should encourage optimism, although is sure frustrating to some scientists cherishing planetary defense projects.

True, popular mass publications often allege that 10 - 12 thousand years ago an asteroid crashed from heaven extinguishing the highly-developed Atlantean civilization, while the giant wave sweeping the world ocean has left its trace in the human lore as the Deluge. However atlantomania belongs to science fiction for lack of a factual evidence.

Nevertheless, the problem of a possible asteroid attack remains. It offers us a challenge: to pool efforts of engineers and scientists of industrial countries to put to peaceful use the colossal backlog of knowledge and technology that has heretofore been used to create mass destruction weapons and means of their delivery to enormous distances.

And one more. Over the recent century, a negligible time in the geologic history, our planet has witnessed enormous changes, including extinction of hundreds (if not thousands) of animal and plant species. Global transformations have been undergone by the composition of the atmosphere and surface waters, weather and climate, and the landscape. The upcoming decades are likely to witness a substantial aggravation of the ecological situation resulting in catastrophic consequences.

Casting alarmed glances up into the outer space, the contemporary man, preoccupied with the problem of an "anti-asteroid umbrella", is involuntarily distracted from a much more realistic threat posed by the accelerating pollution, contamination and degradation of biosphere. For it the technogenic effect is more perilous and destructive than a hypothetical unidentified heavenly object approaching Earth.

Novy Vek magazine, 2003

Prepared by Rudolf BALANDIN

^* See: Yu. Avsyuk et al., "Did Dinosaurs Die Out Suddenly?", Science in Russia, No. 3, 2002. - Ed .

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