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Objects that could hit the earth Tugging off the threat Prof Yash
Pal THIS UNIVERSE |
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Objects that could hit the earth
Apophis is one of about 20,000 Near-earth Objects (NEOs) — including asteroids, meteorites and comets — which are space rock left over from the formation of the solar system. “Asteroid” means “minor star”, but most asteroids are tiny planets rotating around the sun between the orbits of the planets Mars and Jupiter (the “asteroid belt”). Most NEOs are believed to the asteroids that were knocked out of the asteroid belt by collisions with other asteroids or by the gravitational force of the giant planet Jupiter. Meteorites are smaller space rocks, some of which enter the earth’s atmosphere and get burnt out by atmospheric friction before they reach the Earth’s surface; these are the familiar ‘shooting stars’. Comets are small, irregularly-shaped bodies composed of non-volatile grains and frozen gases; they have highly elongated orbits that bring them close to the Sun and out into space, beyond the orbit of the planet Pluto. In his 1973 novel Rendezvous with Rama, Arthur C. Clarke visualised Project Spaceguard, a project designed to protect Earth from objects in space. We might have to devise something like that as protection from unwelcome visitors from space. A visit from planet-crossing objects is no chimaera. About 50,000 years ago, a meteorite or comet hit Lonar (in Buldana) about 550 km from Mumbai, creating a crater 1.6 km in diameter. It is the world’s largest crater in basaltic rock and ranks as one of the world’s five largest craters. About 50,000 years ago, an asteroid about 50 metres wide hit Arizona in the USA, gouging a hole in the ground, 200 metres deep and one kilometre wide, known as the Great Meteor Crater. The asteroid or meteorite that hit the Earth towards the end of the Cretaceous period (65 million years ago) and is linked with the fade-out of the dinosaurs is believed to have been six miles in diameter. Again, on June 30, 1908, an object described by witnesses as being brighter that the Sun, came down over the Tunguska region of Siberia, exploding several kilometres above the Earth’s surface; this body is believed to have been 330 feet in diameter. The precise effect of an impact with the earth would depend upon the mass of the asteroid, the angle of the impact the material of which the asteroid is made. An asteroid between one and two kilometres wide would cause devastation having the energy of several billion tons of TNT. However, even if a NEO does not impact the earth, it could cause an explosion resulting from heating in the rock as well as the atmosphere. NASA is already tracking objects bigger than Apophis, which are at least 3,300 feet in diameter. NASA’s Spaceguard Survey has discovered that more than half the NEO s are larger than one kilometre in diameter.
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Tugging off the threat In principle, asteroid hazards are the only natural hazards that we can eliminate entirely. Various approaches are being worked out. A NASA programme found that non-nuclear kinetic impacts would be the most mature approach to deflect the course of solid NEOs. According to Ed Lu, a veteran of the International Space Station, the most favourable approach for dealing with a NEO on a collision course with earth would be to dispatch a Gravity Tractor. The Gravity Tractor would maintain a position near the asteroid, exerting a gentle tug that would deflect the asteroid. An asteroid as big as Apophis would take about 12 days of tugging. If the Gravity Tractor is launched early enough, less energy would be required to alter the asteroid’s course; the chances of a successful outcome would be greater, too. The best place for spotting 90 per cent of all near-earth asteroids, down to a size of 140 metres, would be the planet Venus, according to a report by NASA, made on March 8, 2007. Space rocks within the Earth’s orbit are most likely to be lost in the Sun’s glare. But from the orbit of Venus, “you’re always looking away from the Sun”, NASA’s Lindley Johnson told the journal New Scientist. Among NASA programmes are a human-piloted visit to a NEO. Such a mission would consume less energy and time than a Mars mission. In the mid-1980s, the noted astronomer Eugene Shoemaker advocated a NEO mission as the very easiest mission beyond the moon. Tom Jones, a veteran of four space Shuttle flights, has said that the Shuttle’s proposed successor, the Crew Exploration vehicle, could be the nucleus of an asteroid mission. In February 2001, a NASA spacecraft named NEAR Shoemaker, which was launched to collect data from the NEO 433 Eros, made an unscheduled landing on the asteroid — the first-ever.
— P.K. |
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THIS UNIVERSE If we tie a stone with string and start revolving it and then let it go, it flies straight off in a particular direction. What is the reason for this? If you actually do this experiment you would notice that the stone keeps trying to get away from you all the time. That is the reason the string remains taut. Therefore it does go off if you release the string, or the string breaks off. What this shows is that a moving thing will go on moving in a straight line if there were no force acting on it. This is the famous law of inertia. It also implies that something that is not moving will stay put till you apply a force on it. This is a famous law first clearly enunciated by Newton. This is the law that causes the planets to go around the Sun. Cricketers and sports men of all games use this. True understanding and use of this law enables us to launch rockets and put satellites in their designated orbits. How do fish get oxygen when lakes turn into ice during winter? Most fish do not need to get their “noses” out of water to breathe. (Remember that whales are mammals and do need to breathe air). Fish extract air that is dissolved in water using their gills. They do not get up to the surface of water for this purpose. But your question will still keep bothering you till you remember that when a lake freezes over it is only the top thin layer that becomes ice. There is a lot of water underneath, which has a lot of air dissolved in it to support the fish through winter months. You must have seen that in small fish tanks that are kept at home we take care to keep blowing in air with a pump to ensure that the fish can breathe. But a big lake or an entire ocean is much bigger and stores lot of air. |
Right now, the movements of a 460-foot-wide space rock, called Apophis, are being monitored by scientists: the rock has a one-in-45,000 chance of hitting the Earth on April 13, 2036. Apophis, which has a mass of 20 million tons, could be heading for the Kamatchatkans and Venezuela.
In principle, asteroid hazards are the only natural hazards that we can eliminate entirely. Various approaches are being worked out. A NASA programme found that non-nuclear kinetic impacts would be the most mature approach to deflect the course of solid NEOs. According to Ed Lu, a veteran of the International Space Station, the most favourable approach for dealing with a NEO on a collision course with earth would be to dispatch a Gravity Tractor.
