it is a rock that floats through space. Sizes vary. They can be big or small and have a variety of shapes. It is thought that quite a few of these rocks are mineral – rich. They may carry rare and valuable ores. It has been estimated that there is enough mineral wealth in the Asteroid Belt, between Mars and Jupiter, to make multi billionaires of all! Much iron has been detected in some of them. Many of them are made of sandy – relatively – light silicates.
These rocks played a very important role in the formation of our solar system. In the beginning of planet formation, they often collided, melted from the heat of impact, and bonded together to form bigger hunks. Eventually they formed planetoids and then planets. Other rocks collided and became smaller planetoids which could be captured by a planet’s gravity. They fell into orbit and became what we call moons.
There are a lot of these rocks floating about. They usually fall under the gravitational influence, or pull, of bigger objects in our solar system. Many form a “belt” between two planets: Mars and Jupiter. Some scientists think that a planet might have broken up and that these pieces are the leftovers. Others believe this is simply space junk that never got to form a new planet.
These rocks perhaps may number in the billions; some are the size of sand grains, peas and softballs. Some are the size of states. Big asteroids can even have micro gravity.
Japan recently scored a major success by sending a probe named Hayabusa to rendezvous with an asteroid. (The probe is expected to return to Earth in 2010.) Hopefully it will bring samples collected from the surface of the asteroid.
The asteroid called Itokawa is 1,800 feet long by 900 feet at its widest point. Its composition seems to be silicate rock, making it a chondrite. Its orbital paths may cause it to be a dangerous object for Earth someday. Space rocks can mean much in your life. They provide entertainment with “shooting stars” and meteor showers. Or they can kill you in gigantic collisions with Earth.
An Example of Concern
may have its flight path altered as it passes us. This is called the keyhole effect. If so, seven years later, when it comes by again, it may well hit us. It is about 1,000 feet in diameter and can cause problems, but in on 69 a regional, not global, scale.
Members of NASA have proposed sending a probe in the near future to study the composition and makeup of the PHA (Potentially Hazardous Asteroid) object. Because of monetary constraints and a feeling that the chances of a hit are about twenty percent twenty three years from now, this mission will not happen in the near term.
As of now, no asteroid has been spotted that is heading for Earth.
The word “comet”, comes from the Greek word kometes, meaning long hair. This refers to the long tails that comets develop when they close in on the Sun. They wander through space, cold and dark, their jagged edges stabbing into darkness until, one day, they move ever so slightly on a new course. Their momentum increases as a strengthening force of gravity pulls them onward.
As the gravitational influence of the sun upon the comet grows, the comet’s speed increases. Eventually, the effects of solar winds and heat come upon it icy surfaces. A brilliant tail forms. The comet becomes a glorious show of light, ice, gas, and streaming particles.
Comets have long been sources of wonder and mystery to planet Earth’s human population. They were thought of as pretenders of great events, in forms of disasters. Comets were dreaded. There are written accounts of them going back over two thousand years.
Although they can be potentially “bad news” to earthlings, they are just natural objects wandering in and around our solar system.
The comets in our solar system are found on an elliptical orbit. They are attracted by the Sun and swing by it before going way out and then coming back in again. Eventually they either run into the Sun and melt, or they hit other objects, such as us!
The famous Halley’s Comet comes around every seventy years; it is like a bus on a schedule. The last time it passed by Earth was in 1986. Many of you may be alive when it passes by again. It has been tracked since the Middle Ages. Another comet, Hale-Bopp, came near to us in 1996. It is over thirty miles long and shaped like an island with mountains.
The head of the comet is called the nucleus. When it enters far enough into our solar system it develops a coma, a halo of particles flying off the comet. The particles trail behind the coma and turn into a long transparent tail. Comas have been seen to extend as far as sixty thousand miles from the surface of the comet, while tails can extend millions of miles into space. An additional feature of a comet is its hydrogen cloud. This cloud surrounds the comet but cannot been seen from Earth.
In 1950 Fred Whipple created a good analogy by describing a comet as “dirty snowballs.” Comets are made of water ice, frozen gases, stony materials and some metal solids. They are much less dense than meteors. There is some surface gravity on larger ones.
Gases coming off the comet contain the following compounds: carbon dioxide, silicates, nitrogen, hydrogen and carbon. All of these are the building blocks of life. What causes all the surface action when a comet comes close enough to the Sun? The Sun’s solar heat causes the frozen gases to defrost, and solar gravity pulls off dust. The gases and dust cannot be held by the comet’s weak gravity, so they go out into space and are captured by the same solar gravitational forces pulling the nucleus. The gases become fluorescent and the dust reflects sunlight. The comet soon becomes very visible. About twenty five of these light streaks are spotted every year.
Once ultraviolet radiation interacts with the gases, it causes the molecules to tear apart. The results are floating free radical particles known as ions. These ions mix with solar winds to form the long tails on the comets.
The ionized hydrogen gases flowing out at the front of the coma produce a bow shock. (This is when gases block the solar winds directly in front of the comet, forcing them off to the sides.)
A probe called Giotto came within 375 miles of Halley’s Comet’s head, or nucleus. It found the nucleus to be very dark, about five miles long by nine miles wide. It rotated at a speed of once every two 71 days. The surface was full of cracks, crevasses and possibly craters. From a portion of the surface gases, water vapor and dust were venting out toward the Sun. Parts of the surface looked blackened as if burned. Perhaps because of Halley’s previous passes near the Sun, frozen surface layers were either blown away or burned off.
Where do these “snow balls” come from? Many comets lie in wait in the farthest edges of our solar system in a place called the Oort Cloud. It is thought to contain as many as one trillion comets.
It was once presumed that all comets are white because of the water ice. This has been disproved. A green comet was observed in 2007 by an amateur astronomer from China. He named it Lulin. It flew by the Earth in 2009.
Why green? The comet gases, containing cyanogen and diatomic carbon, cast a green glow when light hits the particles in a vacuum, such as space.
It does not take much for these comets to start a fatal freefall toward our Sun. Imagine you in front of a comet that is ten miles wide by twenty miles long. Put out your hand and flick it with your finger. You have begun its new journey! At first the motion would not even be noticeable, but over a period of time the speed would increase and thousands of years later there would be another comet in our neighborhood.
Stars occasionally pass within a few light years of our solar system. That influence, that little gravitational change in our part of the galaxy, is enough to set in motion the movement of great mountains of ice and rock, sending these comets towards the Sun.
These comets are very dangerous to us. They are unpredictable. Many are huge. A midsized comet could virtually wipe out life on Earth. One, named Shoemaker-Levy 9, collided with Jupiter in 1994. It had been broken into fifteen chunks by Jupiter’s gravity and hit the planet with one piece after another. One such piece left a bruise on Jupiter that was the size of our planet! Undoubtedly, Jupiter has saved us many times from a collision. Jupiter, the great vacuum cleaner!
The result of another comet impact with Jupiter was witnessed in late 2009. This occurred in the area of Jupiter’s South Pole and left a mark similar to the ShoemakerLevy 9 wound on that planet.
Eventually most comets die a fiery death. We can usually find these large asteroids coming in our direction. If found in time, we might be able to do something about them, but comets are different; often they appear out of the darkness within months of being near to us. There is not enough time to prepare. Don’t let the movies fool you; we are not ready for a large comet!
Meteors and Meteorites
It is well known for its nearly perfect state of preservation.
What is a meteor? Meteors are objects that fall from space into our atmosphere. They can also be called bolides. What is a meteorite? It is a meteor that landed on the ground and did not disintegrate on impact.
Because of their speed these objects become engulfed in flames when they hit our air. They can either explode in the air or reach the ground. When they do hit, they cause devastation in proportion to: their size, what they are made of, and how high the combined speed is between Earth and the crashing objects.
Many meteorites are stony, made of silicate minerals (about 94% of all recovered rocks). Some are igneous rocks, others are mostly metal (iron meteorites) and many are a mix of both materials. Meteorites called Chondrites are composed of elements that can be traced back to the times when our solar system was being formed. Some meteors are comets ranging from the size of basketballs, (which fall onto our planet daily); to objects that are miles wide and can cause an extinction level event. (This is when much, or even all, planetary life could be destroyed by a collision).
Meteors may break up and hit the ground like a shot gun blast, or they can land in a single piece and create impact craters. These small rocks entering in our atmosphere in groups are called meteor showers. Large meteors coming through the atmosphere are accompanied by brilliant streaks of light and loud roars. When the meteorites are recovered after landing they are called falls.
When meteors hit the atmosphere they heat up and form a glass-like crust called a fusion crust. Pieces of this type of glass are commonly found near impact craters.
Meteorites have been found in many areas of the world, but most of the samples have been located in Antarctica. So far the samples found in that region represent about 3,000 different meteorites.
Near Earth Objects are mainly asteroids, but they can also be short term comets that are orbit the Earth or crossing its orbital path around the Sun.
There are two different types of asteroids and comets to look for. One type 73 are the NEOs or “Near Earth Objects”. The newest term is PHAs, or “Potentially Hazardous Asteroids”. As of January 2010, 1,086 have been found. These rocks in space can come within 4,500,000 miles of Earth and are more than 500 feet in diameter. They represent 90% of the danger in space. They are fairly easy to find. They are in our neighborhood and therefore more readily spotted. The other dangerous space objects are called intermediates and long terms. They are mostly comets. They may take years to drop by and will give us only months of warning of their arrival.
There are scientists watching for large asteroids that may cross our path. These scientists have developed an impact scale from 1 to 10, in case one of these objects does head for Earth. Zero implying virtually no damage, while a scale of 10 represents a catastrophe. The estimate is that there are at least two thousand NEOs cross our orbital highway every year. Many of them could cause the death of hundreds of thousands if they hit us. Some could kill us all.
Many of these objects have been spotted. However, there are few astronomers looking for them due to budgeting problems. Over time, we see less and less of these objects because they have already been drawn in by Earth’s gravity, or they hit the Moon, or have been absorbed by the Sun.
Every day many tons of this debris still hits the Earth’s atmosphere but is in pieces so small that they cause little concern and on occasion entertain us when see as “shooting stars”.
Near Earth Objects are mainly asteroids, but could also be short term comets that are orbiting the Earth or crossing its orbital path around the Sun.
About every 100 years, a rather large (50 yards wide), iron asteroid may hit the earth. Every few hundred thousand years an object can reach the Earth that could cause wide destruction and radical changes in planetary climate.
A famous example of a meteoric event took place in 1908 over Tunguska, Siberia, Russia. A large meteor with an estimated weight of one hundred thousand tons entered the atmosphere. It is believe that it was a comet. It exploded a few miles above the surface of the Earth. The explosion knocked down over one thousand square miles of trees. It had the force of hundreds of atom bombs.
Luckily, this part of Siberia had no human population, and the loss was limited to plants and animals. But the planetary effect was so great that it was virtually day light in London during the middle of the night, even though the blast was five thousand miles away! The sound wave from the blast circled the planet twice! Had it hit the Earth five hours earlier, the Moscow area would have been wiped out.
The largest meteor crater in the United States, found near Winslow, Arizona, is called the Barrington Crater. About three quarters of a mile across and nearly six hundred feet deep, it was caused by the impact of an iron meteorite weighing almost thirty tons.
The most famous crater is located off the Yucatan peninsula in Mexico. Called Chichlxu, it is over 150 miles wide and 74 perhaps twenty miles deep. (Remember, that is about the average thickness of the Earth’s crust.) The ejected rocks were thrown far into space. The composition of the burned rocks produced a poisonous gas. Fires throughout the Earth occurred. There was a dramatic lowering of temperature. During that time, there were no ice caps.
This collision with Earth happened about sixty five million years ago, during the Cretaceous Period, the age of the dinosaurs. No fossils of dinosaurs can be found beyond the age of this impact. All over the Earth there is a thin line of iridium found in the sixty five million year level of rocks and soil. Once this event level is located, fossils are not being found in abundance until another level representing the Earth’s surface five thousand years later.
Can this happen again? Most certainly! If a large rock or comet as big as six miles wide or more hits our planet, the devastation will be enormous. One would see earth waves hundreds of feet high. Tsunamis (Fast moving walls of water in the ocean) hundreds or even thousands of feet high, would sweep over much of any nearby coastal lands. Blazing debris from the impact would fall over the surface of the earth. The showers of rocks could be as big as a twenty story office buildings, and fires would rage planet wide. Faults would open up from the tremendous shaking and creating earthquakes. The searing heat would kill most plant life. The dense, choking smoke would soon blot out all sunlight, plunging our planet into freezing cold, with darkness so deep that eyes could be useless. Our planet grows silent and still for perhaps hundreds, or even thousands of years. No structure would be left standing. Any traces of human existence would fade until only a few fossilized foot prints and bones would tell someone in the future that we once existed. We could be the next oil deposit.
Asteroids can be charted to see if they have a chance of crossing our path far in the future. By tracking these objects, we should have years of forewarning and they have chance to use technology to change their course. We could change the velocity of the asteroid comet, but not blow into pieces creating debris that cannot be controlled. When given a warning, far in advance, of an object that may collide with earth the craft sent to intercept it will need less efforts to have the object’s speed and or course adjusted.
Meteorites can be seen in science museums and exhibits around the world. Some have been made into jewelry or pieces of art. Others have been worshiped; it is thought that the great Kaba stone in Mecca, Saudi Arabia, is a meteorite. It is located at the center in an area where millions walk in a circle as they complete their Muslim pilgrimage to Mecca.
One meteorite, discovered in 75 Antarctica, had a profound influence on mankind. When opened, researchers found what appear to be fossils of tiny animals (micro-organisms). The chemical composition of the rocks was traced back to Mars. Millions upon millions of years ago, a large meteor hit Mars. Some Martian rocks were hurled so far that not only did they make it into space, but they even escaped Mars’ gravity. Eventually some of those rocks fell to Earth.
Comet-meteors may also account for many of our oceans. The process of billions of those “dirty snow balls” entering our atmosphere has made us water and oxygen rich. Thus, these menacing objects from the sky may support life as well as take it away.