When worlds and comets collide

ROSHNI GURUNG

The greatest collision between a planet and another celestial object ever witnessed by scientists happened in July 1994. For six days, the comet Shoemaker-Levy 9 bombarded the planet Jupiter. One after another, more than 20 comet fragments slammed into Jupiter’s atmosphere at a speed of 60 km per second creating enormous fireballs easily visible through telescopes on Earth. The impact not only thrilled scientists and amazed the world but also served as a reminder that the Earth can be a dangerous place to live in.

If the Earth had been the target of the comet Shoemaker-Levy 9, scientists predict that the effect of the impact would have been truly inconceivably catastrophic, equivalent to a billion Mega-tons of hydrogen bombs exploding at once. Trillions of tons of pulverized debris would be thrown into the atmosphere, where it would blot out the sun for years. Much of our planet’s vegetation, animal life would die and with it the human race. Civilization will be destroyed and whatever scattered remnants of humanity survived – if any did – it would sink into millions of years of a prolonged dark age, to begin a new evolution process.

The earth has been hit many times in the past by huge objects hurling from space. Scientists believe that a mammoth collision with a large comet occurred 65 million years ago which may have led to the extinction of species at the end of the Cretaceous era. Many animals and plants, including the dinosaurs vanished forever from the Earth. Geologists think they may have identified the ancient crater produced by that event off the coast of Mexico’s Yucantan Peninsula. Fortunately, such magnitude collisions are very rare because the geological record of impact craters on Earth show that a 10 km wide alien object at a speed of 50 km per second strikes our planet only once every one hundred million years. Nevertheless, strikes by smaller bodies are more frequent, simply because small objects in the solar system are much more numerous than larger ones. The great majority of strikes have occurred in the ocean because more than 70 percentage of the Earth is covered with water. The scarcity of seeing impact craters on land is due to erosion – as centuries pass by wind and water slowly obliterate all traces of most craters.

The best-preserved impact crater made 50,000 years ago is the crater in Arizona desert. An iron meteorite 30 meters in diameter smashed into the Arizona desert to produce a crater of depression 1.2 km across and 175 meters deep with an explosive force of 20 million tons of TNT. Similarly, in 1908 a meteor of 100 meters in diameter levelled more than 2000 square kilometres of forest near the Tunguska River in central Siberia. An Arizona sized explosion on a populated area would be a calamity, but the destruction would be limited to a relatively small area. The heavenly object would smash into the ground with incredible force and explode in an immense fireball. The blast would produce a crater 20 km across, several kilometres deep and virtually everything within 100 km radius would be reduce to ashes. Beyond the ring of total destruction, damage from the shock wave and heat would be severe to moderate for another 1000 km. The force of the impact would hurl molten material and eject immense volume of dust, gas and vaporised rock into the atmosphere that would spread around the planet and obscure the sun. It will affect the global climate and cause widespread crop failures and starvation. The greatest affect would be a huge loss of human life.

But, what about the Arizona comet dimension that spares a city and strikes far out at sea?. The comet after it plunge through the atmosphere at immerse speed would plod through several kilometres of seawater in a fraction of a second exploding with a titanic blast in the sea floor creating a crater more than 10 km in diametres, spewing materials in all directions. This would create a tidal wave several kilometres in height that would surge outward at a speed of 1000 km per hour affecting the coastline countries. Scientists estimate that a comet, meteor, or asteroid collision into the Earth of an Arizona size would occur every 200 to 300 years on the average. However, there are countless other bodies orbiting out in space.

It is possible – not likely – but possible, that the Earth will be hit in the next 100 years by some large extraterrestrial object that astronomers have not discovered yet. To protect the planet, experts say its worth considering how such a disaster might be prevented. Astronomers have proposed the construction of a global network of telescopes dedicated in searching the solar system for all near-Earth large-scale objects of diameters 1 km or more whose path would cross the Earth in the future. Fortunately, detecting a comet on collision course with the Earth will undoubtedly be easy than preventing the impact. So far, scientists and engineers have proposed several schemes, but all involve considerable high risks.

One solution is to send a nuclear-armed rocket into space and detonate warheads close enough to the target to affect its motion to push it into a new orbit. Only a small change in path of a comet would make a large difference over a distance of several billion kilometres eventually diverting it in hitting the Earth. However, such a mission would require extremely accurate calculations to give the rocket just the right trajectory, time and explosion. Scientists say that what has happened to the Earth in the past will happen again in the future. The only question is when.

(The author is an undergraduate student at Malpi International College)

The unheard story of @

Sudan Jha

We are all familiar with the "@" sign. In fact, whenever we talk about any e-mail account, the "@" sign is widely used. So, what is "@" all about. How was this sign used?

In 1972, Ray Tomlinson, a computer engineer, sent the first electronic message, now known as email, using the @ symbol to indicate the location or institution of the e-mail recipient. The logical choice for Tomlinson was the "at sign," both because it was unlikely to appear in anyone’s name and also because it represented the word "at," as in a particular user is sitting @ this specific computer. However, before the symbol became a standard key on typewriter keyboards in the 1880s, the @ sign had a long if somewhat sketchy history of use throughout the world.

Linguists are divided as to when the symbol first appeared. Some argue that the symbol dates back to the 6th or 7th centuries when Latin scribes adapted the symbol from the Latin word ad, meaning at, to or toward. The scribes, in an attempt to simplify the amount of pen strokes they were using, created the ligature (combination of two or more letters) by exaggerating the upstroke of the letter "d" and curving it to the left over the "a." Other linguists will argue that the @ sign is a more recent development, appearing sometime in the 18th century as a symbol used in commerce to indicate price per unit, as in 2 months @ 10 rupees.

The biggest problem with the @ sign nowadays is what to call it. Spaniards and Portuguese still use "arroba", meaning a standard of weight and the French have borrowed it and turned into "arobase" and the Americans and Britons call it the "at-sign." The Germans call it as "at-Zeichen", Estonians "ät-märk" and Japanese "atto maak".

However, in most languages the sign is described using a wide spectrum of metaphors lifted from daily life. References to animals are the most common. Germans, Dutch, Finns, Hungarians, Poles and South Africans see it as a monkey tail. The snail - oddly enough for the anti-snail-mail set - portrays the @ sign not only in French "petit escargot" and Italian "chiocciola", but also in Korean and Esperanto "heliko". Danes and Swedes call it "snabel-a" - the "a" with an elephant’s trunk; Hungarians a worm; Norwegians a pig’s tail; Chinese a little mouse; and Russians a dog. Food offers other tantalising metaphors. Swedes have borrowed the cinnamon bun "kanelbulle". Czechs have been inspired by the rolled pickled herring "zavinac" commonly eaten in Prague’s pubs. My favourite, though, is the Finnish "miukumauku" - the "sign of the meow"- inspired by a curled-up, sleeping cat.

So what do we call it? The @ sign appears to be one of the few survivors of the dot-com shakeout. It’s part of the electronic identity of hundreds of millions of Internet users, and dozens of companies have tried to hijack it - together with the values of modernity, connectivity and speed that it embodies - by embedding it into their names. But usage of the @ sign to replace or "enhance" current words is also spreading. In Spain, the @ sign is increasingly used by youngsters as a politically correct way of avoiding specifying gender: Despite what it is called or what is should be called, one thing is certain, the @ sign is here to stay.

Chile’s hole in the sky

Larry Rohter

Everything is different here at the bottom of the world, starting with the weather. Before Alejandra Mundaca lets her two children go out, she checks the forecast for the temperature, the chance of rain and the level of ultraviolet rays.

For the last decade, the hole in the ozone layer over Antarctica has been growing larger and recently expanded over Punta Arenas, the southernmost city on the planet. Its 125,000 residents have reluctantly learned to adapt. They closely watch the color-coded warnings of a "solar stoplight" publicized on television and radio, and even posted on street corners. Even on warm days, most people wear jackets or long-sleeved shirts or blouses. Many wear sunglasses and make sure to apply 50-proof sunblock even when the sky is blanketed in clouds.

"Life has changed a lot for us over the past few years, and I know that my sons are not going to be able to enjoy the same kind of childhood that I had growing up here," said Mundaca, 33, a schoolteacher. "We used to look forward to spring as relief from the long harsh winter, but now it is a time of maximum peril for all of us who live here." The ozone layer is a thin covering of gas in the stratosphere that absorbs most of the sun’s ultraviolet rays. Since scientists first discovered the hole over Antarctica in the mid-1980s, it has nearly doubled in size and now covers an area larger than North America during the Southern Hemisphere spring. The arms of the hole occasionally extend as far as southern Chile and Argentina.

On a typical day here in December, the solar stoplight was set at orange, the second highest of four levels, and people were warned to limit their exposure to the sun between noon and 3 p.m. to 21 minutes at most. "When the light is red, I don’t let my kids go out to play at all," Liliana Navarro Torres said, referring to Kimberley, 6, and Jonathan, 4. "They don’t like it much, and sometimes it drives me crazy to have them running around the house, but that’s the way it has to be when you live here."

The growth of the ozone hole is attributed largely to chlorofluorocarbons, or CFCs, that were widely used in aerosol sprays and refrigerants until a 1987 agreement was reached to phase them out. But scientists also say that global warming may be contributing to the phenomenon. During much of the 1990s, there was resistance here to accepting signs that the risks to people were growing. The warnings of scientists like Bedrich Magas of Magallanes University, one of the first to emphasize the potential dangers, were dismissed by locals who feared a drop in tourism. But that changed in September 2000, when the ozone hole opened directly over Punta Arenas. The Socialist government responded with a far-reaching prevention and education program that has become visible everywhere.

"It’s a new way of living," said Lidia Amarales Osorno, the regional director of Chile’s Health Ministry in Punta Arenas. "You’ll see the solar stoplight posted in supermarkets, offices and schools, and we even have an ozone brigade to raise consciousness about this problem." In elementary schools, a giant penguin named Paul leads a permanent campaign to teach children the steps they need to take to protect themselves. Many schools also hoist a flag each morning to alert their pupils’ families of the expected level of ultraviolet rays. In some poor neighborhoods, free skin creams are distributed to youngsters. "But the truth is that there is only so much that we can do here ourselves," Amarales said. To everyone’s surprise, the situation has been relatively mild this year. The ozone hole split in two for only the second time since monitoring began, with only the smaller part passing over Punta Arenas. Winds have been calmer than usual, and the hole has begun to retract earlier than usual.

But scientists in the region warn that the problem may persist until the middle of the century and may worsen through the decade. Scientists have also reported the appearance of smaller ozone holes in central Chile, and health officials say that the incidence of melanoma, the most common form of skin cancer, in Santiago, the country’s capital, increased by 105 percent between 1992 and 1998. Because solar radiation reaches the ground at a more acute angle here than in places farther north, Punta Arenas may actually be at less risk than other parts of Chile. But this time of year, atmospheric scientists from all over the world flock here, drawn by the opportunity to study a rare and little-understood phenomenon. Their presence, rather than reassuring residents, only adds to their sense of unease.

"We feel like we are rabbits in a laboratory experiment," said Ivan Mansilla Vera, 36, an engineer and father of two young children. "Nobody knows what is going to happen to us."

International Herald Tribune.

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