Read out Anytime the next space bomb can hit. Hundreds of minor planets and comets cross the orbit of our planet. Some of them will eventually collide. They can devastate the earth and threaten the continuity of humanity. But a cosmic hammer blow is not a fiction. For example, 15 million years ago a stone meteorite reduced a thriving landscape to rubble and ashes on the Swabian-Franconian Alb between Ulm and Nuremberg. Even today, a 24-kilometer crater bears witness to this: under the name Nördlinger Ries, it is world-famous.

What is happening here is no less dramatic than the sci-fi scenarios of the two disaster films: Suddenly, a bright fireball shines in the sky. Nothing is heard at first, because the cause of the luminous phenomenon rushes from the depths of space to the earth at more than 70, 000 miles an hour. With several times the speed of sound, the cosmic intruder, about a kilometer in size, crashes within seconds.

He pierces the earth's atmosphere like a lance lance. Slowed down by the air resistance to still 40, 000 kilometers per hour, the space bomb bores immediately afterwards with brute force into the Jura mountains and beats a huge crater into the landscape. After only 0.03 seconds, the now gas-fired projectile comes to a standstill more than one kilometer deep in the earth and explodes. A shock wave rages through the crust of the earth and smashes the rock to six kilometers deep. A moment later, the rock vapor breaks out of the center of the crater with tremendous force. The noise breaks every eardrum. In the short term, there is a pressure of about ten million bar and a heat of 30, 000 degrees - that's five times as hot as on the sun's surface.

Then the crushed, molten or vaporized rock is spewed out of the earth. Parts of it reach within a minute up to 30 kilometers high in the trembling atmosphere of thunder. After 20 seconds, the crater is already 15 kilometers wide and 4.5 kilometers deep. At its edge, the ejectors pile up several hundred meters high. Now the ground bounces back and shoots up a few hundred meters. The debris thrown into the air splash back onto the earth and form a closed, 30 to 40-meter-thick blanket within a radius of 50 kilometers. The glowing cloud collapses and sets alight, which can still catch fire. Massive rocks are slipping in from the rim of the crater and widening it to 20 to 25 kilometers. Ten minutes after the impact, the booming earth comes to rest. 6500 square kilometers of land are devastated. Within 100 kilometers there is no life left. display

That collisions of celestial bodies are real, has been clearly demonstrated to us at the latest in the week of 16 to 22 July 1994. At that time, nearly two dozen pieces of comet set up a fireworks display on Jupiter. Through the gravitational field of the giant planet, the parent body of the fragments had been torn in July 1992 during its near flyby. Some of the chunks, at most a few hundred meters in size, released energies of a multiple of the entire Earth's nuclear arsenal. Exploding fireballs, thrown back by the impact energy and three times as hot as the sun's surface, rose 3, 000 kilometers above the Jupiter's atmosphere. Within a few hours, the comet debris and chemical reactions in the Jupiter atmosphere formed dark patches in the Earth's atmosphere, some of them larger than the diameter of our Earth, remaining visible for many months, and even observable with amateur telescopes.

=== Rüdiger Vaas

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