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Looking Up: Asteroid risks to human life by Charles H. Grace There is a possibility that an asteroid will wipe out humankind, as happened to the dinosaurs. But we can still sleep tonight. The dinosaurs didn’t have computer-assisted tracking or guided missiles. DEFINITIONS Tunguska: A remote area in Siberia where in 1908 an asteroid (or comet) exploded 3 miles above the Earth. It caused physical damage comparable to the bomb at Hiroshima although the object was only about 130 feet wide. Reindeer herders 50 miles away were knocked down. Asteroid: A rocky body without atmosphere that orbits the Sun but is too small to be a planet. Asteroid belt: A region between Mars and Jupiter where about 95% of known asteroids circulate. Some maverick asteroids come inward and cross the orbit of the Earth. Large asteroids: Among those asteroids that cross Earth’s orbit, there seem to be only 1,000 or 2,000 that are a mile wide or more. The devastating Yucatan asteroid of 65 million years ago was 5 miles wide. A large one could hit the Earth tomorrow, but maybe not for a thousand years. We’ll probably be able to defend ourselves better 20 or 30 years from now. Small asteroids: Asteroids that are less than 150 feet across are much more numerous. The orbits of a hundred thousand of them cross Earth’s path, and although small they can be deadly. Impact: Damage depends on whether the object strikes Earth on land or ocean. An ocean impact is worse and 70% of Earth’s surface is ocean. A tsunami wave caused by an asteroid could be a hundred times taller than the recent earthquake-caused tsunami that killed thousands of people. If it hits on land, an asteroid only 500 feet wide could destroy a large urban area. A mile wide-asteroid could immediately wipe out all life in a large part of the Earth near where it strikes, and severely disrupt the rest of the Earth. The dust it raises could block the Sun long enough to kill food crops and create worldwide famine. Detection methods: Telescopes on Earth can detect large asteroids but can’t detect objects as small as the 130-foot Tunguska one until they are dangerously close. Protection: Earth can be protected from an approaching asteroid by either destroying or deflecting it. Destruction: This method requires breaking the asteroid into small enough pieces that they will burn up in our atmosphere. An intruding asteroid could be blown apart by a nuclear bomb. Deflection: This method requires that an approaching asteroid be deflected perpendicularly to its trajectory. The Earth’s radius is 4,000 miles, so the new path preferably misses the center of the Earth by 5,000 miles or more. An asteroid could be deflected by exploding a nuclear bomb near it, by striking it with a missile of great momentum or by landing a thrusting device on it and pushing it away. Deflection by thrusting: The earlier a pulse of deflecting thrust is applied, the less thrust is required, because there is more time for the altered trajectory to diverge before it gets near the Earth. If the asteroid were pushed slowly and steadily for several months until it passes us, a greater thrusting acceleration would be required to ensure a safe clearance. Forecasts: Cosmologists think that a billion years from now the Earth’s environment probably won’t be habitable for humans because of solar system aging. Nostradamus, a sixteenth-century French physician and astrologer, prophecied that the world would end in the year 3797. The Bible also predicted an end, but didn’t say when: "Heaven and Earth will pass away...But of that day and hour no one knows, not even the angels of heaven, nor the Son, but the Father alone." Mathew 24:35-36. Some astronomers think it is quite possible that an asteroid will destroy civilization within the next million years. Risk: The chances of our dying by asteroid are estimated to be the same as those of dying in a plane crash, i.e., about one in twenty thousand. There are other threats to worry about that are more likely. References:
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Two decades of scrutinizing Saturn are paying off, as scientists have discovered a wave pattern, or oscillation, in Saturn's atmosphere only visible from Earth every 15 years. The discovery of the wave pattern is the result of a 22-year campaign observing Saturn from Earth (the longest study of temperature outside Earth ever recorded), and the Cassini spacecraft's observations of temperature changes in the giant planet's atmosphere over time. The Cassini infrared results, published in Nature, indicate that Saturn's wave pattern is similar to patterns found in Earth's upper atmosphere and on Jupiter. -- JPL Press Release
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