October 10, NASA Earth, our home, is the third planet from the sun. It's the only planet known to have an atmosphere containing free oxygen, oceans of water on its surface and, of course, life. Earth is the fifth largest of the planets in the solar system.
See Article History Earth impact hazard, the danger of collision posed by astronomical small bodies whose orbits around the Sun carry them near Earth. These objects include the rocky asteroid s and their larger fragments and the icy nuclei of comet s.
Space in the vicinity of Earth contains a great number of solid objects in a range of sizes. They are also the least dangerous; they either burn up in the atmosphere or settle to the surface as dust.
Of the somewhat larger objects—i. However, there are occasional reports of roughly softball-sized meteorite fragments damaging houses or cars, and in more than 1, people in the Chelyabinsk region of Russia were injured, mostly by flying glass, when a meteorite 17 metres 56 feet wide broke up in the atmosphere.
The apparently only verified case of a meteorite hitting and injuring a human being occurred in Reports of falls of meteorites with masses in the one-ton range are less frequent; when these objects strike the ground, they can excavate craters a few metres across.
It is only the biggest projectiles, those that collide with Earth very infrequently on average, that are acknowledged to pose a great potential danger to human beings and possibly to all life on the planet. Recognition that such a danger might exist dates back at least to the English astronomers Edmond Halley and Isaac Newton and their work on the Great Comet ofwhose orbit they showed crossed that of Earth.
Modern interest was rekindled in when the experimental physicist Luis Alvarez of the University of CaliforniaBerkeley, and colleagues presented evidence that the impact of an asteroid or comet having a diameter of about 10 km 6 miles was responsible for the mass extinction at the end of the Cretaceous Period The consequences would include a decrease in the amount of sunlight reaching the surface and a prolonged depression of surface temperatures—a so-called impact winter—leading to loss of photosynthesizing plant life and worldwide starvation and disease.
The cloud of dust and carbon gases that resulted is thought by some scientists to have been the cause of the extinction of the dinosaurs. The buried structure, which measures at least km miles across, is thought to be the scar remaining from the impact 65 million years ago of an asteroid or comet measuring perhaps 10 km 6 miles in diameter.
Sharpton, University of Alaska, Fairbanks; NASA In the early s astronomers in the United States, followed by those in several other countries, began studies aimed at better defining the risk posed by cosmic impacts, developing programs to detect threatening objects, and determining if anything could be done to protect Earth from the most devastating impacts.
One outgrowth of these efforts was the development of a scale for categorizing the potential impact hazard of objects newly discovered to be orbiting near Earth.
Short-period comets complete their orbits in less than years and so likely have been observed before; they generally approach along the plane of the solar systemnear which lie the orbits of most of the planets, including Earth.
Long-period comets have orbital periods greater than years and usually much greater; they can approach from any direction. These determine the total kinetic energy released. A typical NEO would strike Earth with a velocity of about 20 km 12 miles per second and a typical long-period comet with a greater velocity, 50 km 30 miles per second or higher.
For objects with diameters less than a few hundred metres, their physical properties are important in calculating how much destruction would result, but for larger bodies only the total energy of the impact is important. Hence, most damage assessments are based on the kinetic energy of an impact rather than the diameter or mass of the projectile.
This energy is expressed in millions of tons megatons of TNTthe same units used to quantify the energy released by thermonuclear bomb s. Estimates of the energy released by the impact range between 15 and 40 megatons. A ring-shaped hydroelectric reservoir lake 70 km 40 miles in diameter occupies the centre of the crater.
The original outer rim, which measured km across, has been worn down by erosional processes. The impact that formed the crater is estimated to have happened some million years ago, near the end of the Triassic Period, and may have played a role in the mass extinction of species that occurred about the same time.
This very wide range corresponds to NEOs with diameters from about 50 metres feet to 20 km 12 miles or to long-period comets with diameters about half as large. Objects smaller than about 50 metres would break up high in the atmosphere; the damage would be limited to less than a few hundred square kilometres around the impact point.
For an object at the lower end of this size range, an ocean impact could cause more damage than one on land because it would result in large tsunamis that would devastate coastal areas for many kilometres inland.
The last destructive impact known, called the Tunguska eventoccurred at the low end of this range over land. On June 30,an object thought to be as much as 50 metres feet in diameter exploded over central Siberia, leveling about 2, square kmacres of pine forest.
Frequency of impacts Because there are far fewer large NEOs and long-period comets in space than smaller ones, the chances of a collision decrease rapidly with increasing size.
An impact by a 1-km- 0.Description A 'death comet' will be zipping passed earth just after Halloween this year. The asteroid with a skull-like face will make its second trip near earth in three years after flying a worrisome , miles from our planet on October 31, Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun.
When frozen, they are the size of a small town. When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets.
Read reviews, compare customer ratings, see screenshots and learn more about Doomsday Comet. If you can destroy the generator the asteroid should break up and no longer be a threat to Earth.
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Halley's Comet is arguably the most famous comet. It is a "periodic" comet and returns to Earth's vicinity about every 75 years, making it possible for a human to see it twice in his or her lifetime. Earth was born from a cloud of dust and gas some billion years ago, along with the rest of the solar system.
Somewhere in its early life history, as it grew bigger from picking up nearby rocks and little worlds in its gravitational pull, it acquired water. How is the big question. Some. Comets Have you ever looked up in the sky and seen a little ball creeping by?
If so, did you wonder what it was? That little ball is called a comet. Comets are small, fragile, and irregularly shaped. Most are composed of frozen gas.
However, some are composed of frozen gas and non-volatile.