Solar system
The solar system consists of 8 planets and 5 dwarf planets.It also has a lot more things like the Sun, the Stars, the Asteroids, the Meteoroids, the Comets and the asteroid belt.The planets are Mercury,Venus,Earth,Mars,Jupiter,Saturn,Uranus and Neptune.The dwarf planets are Pluto,Eris,Makemake,Haumea and Ceres. In actual Ceres is in the asteroid belt but I mentioned it after.
Kuiper Belt Objects
Beyond the gas giant Neptune lies a region of space filled with icy bodies. Known as the Kuiper Belt, this chilly expanse holds trillions of objects, remnants of the early solar system. Dutch astronomer Jan Oort first proposed in 1950 that some comets might come from the the solar system’s far suburbs. That reservoir later became known as the Oort cloud. Earlier, in 1943, astronomer Kenneth Edgeworth had suggests comets and larger bodies might exist beyond Neptune. In 1951, astronomer Gerard Kuiper predicted the existence of a belt of icy objects that now bears his name. Some astronomers refer to it as the Edgeworth-Kupier Belt.
Let's take a closer look at this distant section of the solar system and the small worlds most commonly known as Kupier Belt Objects (KBOs) and, in recent years, dwarf planets.
Beyond the gas giant Neptune lies a region of space filled with icy bodies. Known as the Kuiper Belt, this chilly expanse holds trillions of objects, remnants of the early solar system. Dutch astronomer Jan Oort first proposed in 1950 that some comets might come from the the solar system’s far suburbs. That reservoir later became known as the Oort cloud. Earlier, in 1943, astronomer Kenneth Edgeworth had suggests comets and larger bodies might exist beyond Neptune. In 1951, astronomer Gerard Kuiper predicted the existence of a belt of icy objects that now bears his name. Some astronomers refer to it as the Edgeworth-Kupier Belt.
Let's take a closer look at this distant section of the solar system and the small worlds most commonly known as Kupier Belt Objects (KBOs) and, in recent years, dwarf planets.
Artists rendering of the Kuiper Belt and Oort Cloud.
The Kuiper belt is an elliptical plane in space spanning from 30 to 50 times Earth's distance from the sun, or 2.5 to 4.5 billion miles (4.5 to 7.4 billion kilometers). The belt is similar to the asteroid belt found between Mars and Jupiter, although the objects in the Kuiper Belt tend more to be icy rather than rocky.
Scientists estimate that thousands of bodies more than 62 miles (100 km) in diameter travel around the sun within this belt, along with trillions of smaller objects, many of which are short-period comets. The region also contains several dwarf planets, round worlds too large to be considered asteroids and yet not qualifying as planets because they’re too small, on an odd orbit, and don’t clear out the space around them the way the 8 planets do.
Scientists estimate that thousands of bodies more than 62 miles (100 km) in diameter travel around the sun within this belt, along with trillions of smaller objects, many of which are short-period comets. The region also contains several dwarf planets, round worlds too large to be considered asteroids and yet not qualifying as planets because they’re too small, on an odd orbit, and don’t clear out the space around them the way the 8 planets do.
Artist's concept of the dwarf planet Haumea and its two satellites (Hi’iaka and Namaka).
Kuiper Belt formation
When the solar system formed, much of the gas, dust and rocks pulled together to form the sun and planets. The planets then swept most of the remaining debris into the sun or out of the solar system. But bodies farther out remained safe from gravitational tugs of planets like Jupiter, and so managed to stay safe as they slowly orbited the sun. The Kuiper Belt and its compatriot, the more distant and spherical Oort Cloud, contain the leftover remnants from the beginning of the solar system and can provide valuable insights into its birth.
The most crowded section of the Kuiper Belt lies between 42 and 48 times Earth's distance from the sun, the classical Kuiper Belt. The orbit of objects in this region remain stable for the most part, although some occasionally have their course changed slightly when they drift too close to Neptune.
When the solar system formed, much of the gas, dust and rocks pulled together to form the sun and planets. The planets then swept most of the remaining debris into the sun or out of the solar system. But bodies farther out remained safe from gravitational tugs of planets like Jupiter, and so managed to stay safe as they slowly orbited the sun. The Kuiper Belt and its compatriot, the more distant and spherical Oort Cloud, contain the leftover remnants from the beginning of the solar system and can provide valuable insights into its birth.
The most crowded section of the Kuiper Belt lies between 42 and 48 times Earth's distance from the sun, the classical Kuiper Belt. The orbit of objects in this region remain stable for the most part, although some occasionally have their course changed slightly when they drift too close to Neptune.
Kuiper Belt Objects
Pluto was the first true Kuiper Belt Object to be seen, although scientists at the time didn't recognize it as such. The existence of the Belt wasn't realized until scientists discovered a slow moving, small world in the outer solar system in 1992 (David Jewitt and Jane Luu found the KBO, 1992QB1.). Other objects soon followed, and astronomers quickly saw that the region beyond Neptune teemed with icy rocks and tiny worlds.
Sedna (sed’nah), about three-fourths the size of Pluto, was discovered in 2004. It is so far out from the sun it takes about 10,500 years to make a single orbit. Sedna is about 1,100 miles (1,770 km) wide and circles the sun on an eccentric orbit that ranges between 8 billion miles (12.9 billion km) and 84 billion miles (135 billion km).
In July 2005, astronomers announced the discovery of an object in the Kuiper Belt thought to be larger than Pluto, though subsequent observations revealed it was slightly smaller. Known as Eris, it orbits the sun approximately once every 580 years, traveling almost one hundred times farther from the sun than Earth does. Eris' discovery revealed to some astronomers the problem of terming Pluto a full-scale planet, and in 2006, Pluto, Eris, and the largest asteroid Ceres were reclassified as dwarf planets. Two more dwarf planets, Haumea andMakemake, were discovered in the Kuiper Belt in 2008.
Because of their small size and distant location, Kuiper Belt Objects are a challenge to spot from Earth. Infrared measurements from NASA's space-based telescope, Spitzer, have helped to nail down sizes for the largest objects.
In order to catch a better glimpse of these remote leftovers from the birth of the solar system, NASA launched the New Horizons mission. Set to reach Pluto in 2015, the mission’s robotic probe will study the most famous dwarf planet before continuing on with an aim to examine multiple KBOs
Pluto was the first true Kuiper Belt Object to be seen, although scientists at the time didn't recognize it as such. The existence of the Belt wasn't realized until scientists discovered a slow moving, small world in the outer solar system in 1992 (David Jewitt and Jane Luu found the KBO, 1992QB1.). Other objects soon followed, and astronomers quickly saw that the region beyond Neptune teemed with icy rocks and tiny worlds.
Sedna (sed’nah), about three-fourths the size of Pluto, was discovered in 2004. It is so far out from the sun it takes about 10,500 years to make a single orbit. Sedna is about 1,100 miles (1,770 km) wide and circles the sun on an eccentric orbit that ranges between 8 billion miles (12.9 billion km) and 84 billion miles (135 billion km).
In July 2005, astronomers announced the discovery of an object in the Kuiper Belt thought to be larger than Pluto, though subsequent observations revealed it was slightly smaller. Known as Eris, it orbits the sun approximately once every 580 years, traveling almost one hundred times farther from the sun than Earth does. Eris' discovery revealed to some astronomers the problem of terming Pluto a full-scale planet, and in 2006, Pluto, Eris, and the largest asteroid Ceres were reclassified as dwarf planets. Two more dwarf planets, Haumea andMakemake, were discovered in the Kuiper Belt in 2008.
Because of their small size and distant location, Kuiper Belt Objects are a challenge to spot from Earth. Infrared measurements from NASA's space-based telescope, Spitzer, have helped to nail down sizes for the largest objects.
In order to catch a better glimpse of these remote leftovers from the birth of the solar system, NASA launched the New Horizons mission. Set to reach Pluto in 2015, the mission’s robotic probe will study the most famous dwarf planet before continuing on with an aim to examine multiple KBOs
This artist's impression shows the distant dwarf planet Eris. New observations have shown that Eris is smaller than previously thought and almost exactly the same size as Pluto. Eris is extremely reflective and its surface is probably covered in frost formed from the frozen remains of its atmosphere. The distant Sun appears to the upper right and both Eris and its moon Dysnomia (center) appear as crescents.
The Kuiper Belt is shown beyond the orbit of Neptune. One of its inhabitants is Eris, on a highly tilted and eliptical orbit.
Comets: Formation, Discovery and Exploration
A comet is an icy body that releases gas or dust. They are often compared to dirty snowballs, though recent research has led some scientists to call them snowy dirtballs. Comets contain dust, ice, carbon dioxide, ammonia, methane and more. Some researchers think comets might have originally brought some of the water and organic molecules to Earth that now make up life here.
Comets orbit the sun, but most are believed to inhabit in an area known as the Oort Cloud, far beyond the orbit of Pluto. Occasionally a comet streaks through the inner solar system; some do so regularly, some only once every few centuries. Many people have never seen a comet, but those who have won't easily forget the celestial show.
Comets orbit the sun, but most are believed to inhabit in an area known as the Oort Cloud, far beyond the orbit of Pluto. Occasionally a comet streaks through the inner solar system; some do so regularly, some only once every few centuries. Many people have never seen a comet, but those who have won't easily forget the celestial show.
Halley's Comet as photographed May 8, 1910, by Dr. G.W. Ritchey using the 60-inch (1.5-meter) telescope at Mount Wilson Observatory, Calif., during the comet's last appearance. The head of the comet and the beginning of its long tail are shown. Short, straight streaks are background stars.
Physical Characteristics
The solid nucleus or core of a comet consists mostly of ice and dust coated with dark organic material, with the ice composed mainly of frozen water but perhaps other frozen substances as well, such as ammonia, carbon dioxide, carbon monoxide and methane. The nucleus might have a small rocky core.
As a comet gets closer to the sun, the ice on the surface of the nucleus begins turning into gas, forming a cloud known as the coma. Radiation from the sun pushes dust particles away from the coma, forming a dust tail, while charged particles from the sun convert some of the comet's gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and the solar wind, they always point away from the sun.
The nuclei of most comets are thought to measure 10 miles (16 km) or less. Some comets have comas that can reach nearly 1 million miles (1.6 million kilometers) wide, and some have tails reaching 100 million miles (160 million kilometers) long.
We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun. However, most comets are too small or too faint to be seen without a telescope.
Comets leave a trail of debris behind them that can lead to meteor showers on Earth. For instance, the Perseid meteor shower occurs every year between August 9 and 13 when the Earth passes through the orbit of the Swift-Tuttle comet.
Orbital Characteristics
Asteroids classify comets based on the durations of their orbits around the sun. Short-period comets need roughly 200 years or less to complete one orbit, long-period comets take more than 200 years, and single-apparition comets are not bound to the sun, on orbits that take them out of the solar system. Recently, scientist have also discovered comets in the main asteroid belt — these main-belt comets might be a key source of water for the inner terrestrial planets.
Scientists think short-period comets, also known as periodic comets, originatefrom a disk-shaped band of icy objects known as the Kuiper belt beyond Neptune's orbit, with gravitational interactions with the outer planets dragging these bodies inward, where they become active comets. Long-period comets are thought to come from the nearly spherical Oort cloud even further out, which get slung inward by the gravitational pull of passing stars.
Some comets, called sun-grazers, smash right into the sun or get so close that they break up and evaporate.
Naming
In general, comets are named after their discoverer, either a person. For example, comet Shoemaker-Levy 9 got its name because it was the ninth short-periodic comet discovered by Eugene and Carolyn Shoemaker and David Levy. Spacecraft have proven very effective at spotting comets as well, so the names of many comets incorporate the names of missions such as SOHO or WISE.
The solid nucleus or core of a comet consists mostly of ice and dust coated with dark organic material, with the ice composed mainly of frozen water but perhaps other frozen substances as well, such as ammonia, carbon dioxide, carbon monoxide and methane. The nucleus might have a small rocky core.
As a comet gets closer to the sun, the ice on the surface of the nucleus begins turning into gas, forming a cloud known as the coma. Radiation from the sun pushes dust particles away from the coma, forming a dust tail, while charged particles from the sun convert some of the comet's gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and the solar wind, they always point away from the sun.
The nuclei of most comets are thought to measure 10 miles (16 km) or less. Some comets have comas that can reach nearly 1 million miles (1.6 million kilometers) wide, and some have tails reaching 100 million miles (160 million kilometers) long.
We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun. However, most comets are too small or too faint to be seen without a telescope.
Comets leave a trail of debris behind them that can lead to meteor showers on Earth. For instance, the Perseid meteor shower occurs every year between August 9 and 13 when the Earth passes through the orbit of the Swift-Tuttle comet.
Orbital Characteristics
Asteroids classify comets based on the durations of their orbits around the sun. Short-period comets need roughly 200 years or less to complete one orbit, long-period comets take more than 200 years, and single-apparition comets are not bound to the sun, on orbits that take them out of the solar system. Recently, scientist have also discovered comets in the main asteroid belt — these main-belt comets might be a key source of water for the inner terrestrial planets.
Scientists think short-period comets, also known as periodic comets, originatefrom a disk-shaped band of icy objects known as the Kuiper belt beyond Neptune's orbit, with gravitational interactions with the outer planets dragging these bodies inward, where they become active comets. Long-period comets are thought to come from the nearly spherical Oort cloud even further out, which get slung inward by the gravitational pull of passing stars.
Some comets, called sun-grazers, smash right into the sun or get so close that they break up and evaporate.
Naming
In general, comets are named after their discoverer, either a person. For example, comet Shoemaker-Levy 9 got its name because it was the ninth short-periodic comet discovered by Eugene and Carolyn Shoemaker and David Levy. Spacecraft have proven very effective at spotting comets as well, so the names of many comets incorporate the names of missions such as SOHO or WISE.
Comet McNaught C/2009 R1 was visible on June 6, 2010.
Formation
Astronomers think comets are leftovers from the gas, dust, ice and rocks that initially formed the solar system about 4.6 billion years ago.
Comet Life Cycle
History
In antiquity, comets inspired both awe and alarm, "hairy stars" resembling fiery swords that appeared unpredictably in the sky. Often, comets seemed to be omens of doom — the most ancient known mythology, the Babylonian "Epic of Gilgamesh," described fire, brimstone, and flood with the arrival of a comet, and Emperor Nero of Rome saved himself from the "curse of the comet" by having all possible successors to his throne executed. This fear was not just limited to the distant past — in 1910, people in Chicago sealed their windows to protect themselves from what they thought was the comet’s poisonous tail.
For centuries, scientists thought comets traveled in the Earth's atmosphere, but in 1577, observations made by Danish astronomer Tycho Brahe revealed they actually traveled far beyond the moon. Isaac Newton later discovered that comets move in elliptical, oval-shaped orbits around the Sun, and correctly predicted that they could return again and again.
Chinese astronomers kept extensive records on comets for centuries, including observations of Halley's Comet going back to at least 240 BC, historic annals that have proven valuable resources for later astronomers.
A number of recent missions have ventured to comets. NASA's Deep Impactcollided an impactor into Comet Tempel 1 in 2005 and recorded the dramatic explosion that revealed the interior composition and structure of the nucleus. In 2009, NASA announced samples the Stardust mission returned from Comet Wild 2 revealed a building block of life. The European Space Agency's Rosetta is scheduled to orbit Comet Churyumov-Gerasimenko in 2014 and deploy a probe to make the first landing on a comet.
Famous Comets
Halley's Comet is likely the most famous comet in the world, even depicted in the Bayeux Tapestry that chronicled the Battle of Hastings of 1066. It becomes visible to the naked eye every 76 years when it nears the sun. When Halley's Comet zoomed near Earth in 1986, five spacecraft flew past it and gathered unprecedented details, coming close enough to study its nucleus, which is normally concealed by the comet's coma. The roughly potato-shaped, nine-mile-long (15 km) contains equal part ice and dust, with some 80 percent of the ice made of water and about 15 percent of it consisting of frozen carbon monoxide. Researchers believe other comets are chemically similar to Halley's Comet. The nucleus of Halley's Comet was unexpectedly extremely dark black — its surface, and perhaps those of most others, is apparently covered with a black crust of dust over most of the ice, and it only releases gas when holes in this crust expose ice to the sun.
The comet Shoemaker-Levy 9 collided spectacularly with Jupiter in 1994, with the giant planet's gravitational pull ripping the comet apart for at least 21 visible impacts. The largest collision created a fireball that rose about 1,800 miles (3,000 km) above the Jovian cloudtops as well as a giant dark spot more than 7,460 miles (12,000 km) across — about the size of the Earth —and was estimated to have exploded with the force of 6,000 gigatons of TNT.
A recent, highly visible comet was Hale-Bopp, which came within 122 million miles (197 million kilometers) of Earth in 1997. Its unusually large nucleus gave off a great deal of dust and gas — estimated at roughly 18 to 25 miles (30 to 40 kilometers) across — appeared bright to the naked eye.
When Earth crosses the path of a comet, even if the comet hasn't been around for a few years, leftover dust and ice can create increased numbers of meteors in what's known as a meteor shower.
Astronomers think comets are leftovers from the gas, dust, ice and rocks that initially formed the solar system about 4.6 billion years ago.
Comet Life Cycle
- Departure
- Extinction
- Breakup
- Collisions
History
In antiquity, comets inspired both awe and alarm, "hairy stars" resembling fiery swords that appeared unpredictably in the sky. Often, comets seemed to be omens of doom — the most ancient known mythology, the Babylonian "Epic of Gilgamesh," described fire, brimstone, and flood with the arrival of a comet, and Emperor Nero of Rome saved himself from the "curse of the comet" by having all possible successors to his throne executed. This fear was not just limited to the distant past — in 1910, people in Chicago sealed their windows to protect themselves from what they thought was the comet’s poisonous tail.
For centuries, scientists thought comets traveled in the Earth's atmosphere, but in 1577, observations made by Danish astronomer Tycho Brahe revealed they actually traveled far beyond the moon. Isaac Newton later discovered that comets move in elliptical, oval-shaped orbits around the Sun, and correctly predicted that they could return again and again.
Chinese astronomers kept extensive records on comets for centuries, including observations of Halley's Comet going back to at least 240 BC, historic annals that have proven valuable resources for later astronomers.
A number of recent missions have ventured to comets. NASA's Deep Impactcollided an impactor into Comet Tempel 1 in 2005 and recorded the dramatic explosion that revealed the interior composition and structure of the nucleus. In 2009, NASA announced samples the Stardust mission returned from Comet Wild 2 revealed a building block of life. The European Space Agency's Rosetta is scheduled to orbit Comet Churyumov-Gerasimenko in 2014 and deploy a probe to make the first landing on a comet.
Famous Comets
Halley's Comet is likely the most famous comet in the world, even depicted in the Bayeux Tapestry that chronicled the Battle of Hastings of 1066. It becomes visible to the naked eye every 76 years when it nears the sun. When Halley's Comet zoomed near Earth in 1986, five spacecraft flew past it and gathered unprecedented details, coming close enough to study its nucleus, which is normally concealed by the comet's coma. The roughly potato-shaped, nine-mile-long (15 km) contains equal part ice and dust, with some 80 percent of the ice made of water and about 15 percent of it consisting of frozen carbon monoxide. Researchers believe other comets are chemically similar to Halley's Comet. The nucleus of Halley's Comet was unexpectedly extremely dark black — its surface, and perhaps those of most others, is apparently covered with a black crust of dust over most of the ice, and it only releases gas when holes in this crust expose ice to the sun.
The comet Shoemaker-Levy 9 collided spectacularly with Jupiter in 1994, with the giant planet's gravitational pull ripping the comet apart for at least 21 visible impacts. The largest collision created a fireball that rose about 1,800 miles (3,000 km) above the Jovian cloudtops as well as a giant dark spot more than 7,460 miles (12,000 km) across — about the size of the Earth —and was estimated to have exploded with the force of 6,000 gigatons of TNT.
A recent, highly visible comet was Hale-Bopp, which came within 122 million miles (197 million kilometers) of Earth in 1997. Its unusually large nucleus gave off a great deal of dust and gas — estimated at roughly 18 to 25 miles (30 to 40 kilometers) across — appeared bright to the naked eye.
When Earth crosses the path of a comet, even if the comet hasn't been around for a few years, leftover dust and ice can create increased numbers of meteors in what's known as a meteor shower.
Asteroids: Formation, Discovery and Exploration
OSIRIS clear filter image taken during the flyby of the Rosetta spacecraft at asteroid Lutetia on July 10, 2010.
Asteroids are small, airless rocky worlds revolving around the sun that are too small to be called planets. They are also known as planetoids or minor planets. In total, the mass of all the asteroids is less than that of Earth's moon. But despite their size, asteroids can be dangerous. Many have hit Earth in the past, and more will crash into our planet in the future. That's one reason scientists study asteroids and are eager to learn more about their numbers, orbits and physical characteristics. If an asteroid is headed our way, we want to know that.
Most asteroids lie in a vast ring between the orbits of Mars and Jupiter. This main asteroid belt holds more than 200 asteroids larger than 60 miles (100 kilometers) in diameter. Scientists estimate the asteroid belt also contains more than 750,000 asteroids larger than three-fifths of a mile (1 km) in diameter and millions of smaller ones. Not everything in the main belt is an asteroid — for instance, comets have recently been discovered there, and Ceres, once thought of only as an asteroid, is now also considered a dwarf planet.
Many asteroids lie outside the main belt. For instance, a number of asteroids called Trojans lie along Jupiter's orbital path. Three groups — Atens, Amors, and Apollos — known as near-Earth asteroids orbit in the inner solar system and sometimes cross the path of Mars and Earth.
FormationAsteroids are leftovers from the formation of our solar system about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today.
Physical characteristicsAsteroids can reach as large as Ceres, which is 940 km (about 583 miles) across. On the other hand, one of the smallest, discovered in 1991 and named 1991 BA, is only about 20 feet (6 meters) across.
Nearly all asteroids are irregularly shaped, although a few are nearly spherical, such as Ceres. They are often pitted or cratered — for instance, Vesta has a giant crater some 285 miles (460 km) in diameter.
As asteroids revolve around the sun in elliptical orbits, they rotate, sometimes tumbling quite erratically. More than 150 asteroids are also known to have a small companion moon, with some having two moons. Binary or double asteroids also exist, in which two asteroids of roughly equal size orbit each other, and triple asteroid systems are known as well. Many asteroids seemingly have been captured by a planet's gravity and become moons — likely candidates include among Mars' moons Phobos and Deimos and most of the distant outer moons of Jupiter, Saturn, Uranus and Neptune.
The average temperature of the surface of a typical asteroid is minus 100 degrees F (minus 73 degrees C). Asteroids have stayed mostly unchanged for billions of years — as such, research into them could reveal a great deal about the early solar system.
ClassificationIn addition to classifications of asteroids based on their orbits, most asteroids fall into three classes based on composition. The C-type or carbonaceous are greyish in color and are the most common, including more than 75 percent of known asteroids. They probably consist of clay and stony silicate rocks, and inhabit the main belt's outer regions. The S-type or silicaceous asteroids are greenish to reddish in color, account for about 17 percent of known asteroids, and dominate the inner asteroid belt. They appear to be made of silicate materials and nickel-iron. The M-type or metallic asteroids are reddish in color, make up most of the rest of the asteroids, and dwell in the middle region of the main belt. They seem to be made up of nickle-iron. There are many other rare types based on composition as well — for instance, V-type asteroids typified by Vesta have a basaltic, volcanic crust.
Earth impactsEver since Earth formed about 4.5 billion years ago, asteroids and comets have routinely slammed into the planet. The most dangerous asteroids are extremely rare, according to NASA.
An asteroid capable of global disaster would have to be more than a quarter-mile wide. Researchers have estimated that such an impact would raise enough dust into the atmosphere to effectively create a "nuclear winter," severely disrupting agriculture around the world. Asteroids that large strike Earth only once every 1,000 centuries on average, NASA officials say.
Smaller asteroids that are believed to strike Earth every 1,000 to 10,000 years could destroy a city or cause devastating tsunamis.
On Feb. 15, 2013, an asteroid slammed into the atmosphere over the Russian city of Chelyabinsk, creating a shock wave that injured 1,200 people. The space rock is thought to have measured about 65 feet (20 meters) wide when it entered Earth's atmosphere.
Dozens of asteroids have been classified as "potentially hazardous" by the scientists who track them. Some of these, whose orbits come close enough to Earth, could potentially be perturbed in the distant future and sent on a collision course with our planet. Scientists point out that if an asteroid is found to be on a collision course with Earth 30 or 40 years down the road, there is time to react. Though the technology would have to be developed, possibilities include exploding the object or diverting it. [Image Gallery: Potentially Dangerous Asteroids]
For every known asteroid, however, there are many that have not been spotted, and shorter reaction times could prove more threatening.
When an asteroid, or a part of it, crashes into Earth, it's called a meteorite. Here are typical compositions:
Iron meteorites:
NamingSince the International Astronomical Union is less strict on how asteroids are named when compared to other bodies, there are asteroids named after Mr. Spock of "Star Trek" and rock musician Frank Zappa as well as more solemn tributes, such as the seven asteroids named for the crew of the Space Shuttle Columbia killed in 2003. Naming asteroids after pets is no longer allowed.
Asteroids are also given numbers — for example, 99942 Apophis.
ExplorationThe first spacecraft to take close-up images of asteroids was NASA's Galileoin 1991, which also discovered the first moon to orbit an asteroid in 1994.
In 2001, after NASA's NEAR spacecraft intensely studied the near-earth asteroid Eros for more than a year from orbit, mission controllers decided to try and land the spacecraft. Although it wasn't designed for landing, NEAR successfully touched down, setting the record as the first to successfully land on an asteroid.
In 2006, Japan's Hayabusa became the first spacecraft to land on and take off from an asteroid. It returned to Earth in June 2010, and the samples it recovered are currently under study.
NASA's Dawn mission, launched in 2007, began exploring Vesta in 2011 and is slated to explore Ceres in 2015 and will be the first spacecraft to visit either body.
In 2012, a company called Planetary Resources, Inc. announced plans to eventually send a mission to a space rock to extract water and mine the asteroid for precious metals.
Most asteroids lie in a vast ring between the orbits of Mars and Jupiter. This main asteroid belt holds more than 200 asteroids larger than 60 miles (100 kilometers) in diameter. Scientists estimate the asteroid belt also contains more than 750,000 asteroids larger than three-fifths of a mile (1 km) in diameter and millions of smaller ones. Not everything in the main belt is an asteroid — for instance, comets have recently been discovered there, and Ceres, once thought of only as an asteroid, is now also considered a dwarf planet.
Many asteroids lie outside the main belt. For instance, a number of asteroids called Trojans lie along Jupiter's orbital path. Three groups — Atens, Amors, and Apollos — known as near-Earth asteroids orbit in the inner solar system and sometimes cross the path of Mars and Earth.
FormationAsteroids are leftovers from the formation of our solar system about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today.
Physical characteristicsAsteroids can reach as large as Ceres, which is 940 km (about 583 miles) across. On the other hand, one of the smallest, discovered in 1991 and named 1991 BA, is only about 20 feet (6 meters) across.
Nearly all asteroids are irregularly shaped, although a few are nearly spherical, such as Ceres. They are often pitted or cratered — for instance, Vesta has a giant crater some 285 miles (460 km) in diameter.
As asteroids revolve around the sun in elliptical orbits, they rotate, sometimes tumbling quite erratically. More than 150 asteroids are also known to have a small companion moon, with some having two moons. Binary or double asteroids also exist, in which two asteroids of roughly equal size orbit each other, and triple asteroid systems are known as well. Many asteroids seemingly have been captured by a planet's gravity and become moons — likely candidates include among Mars' moons Phobos and Deimos and most of the distant outer moons of Jupiter, Saturn, Uranus and Neptune.
The average temperature of the surface of a typical asteroid is minus 100 degrees F (minus 73 degrees C). Asteroids have stayed mostly unchanged for billions of years — as such, research into them could reveal a great deal about the early solar system.
ClassificationIn addition to classifications of asteroids based on their orbits, most asteroids fall into three classes based on composition. The C-type or carbonaceous are greyish in color and are the most common, including more than 75 percent of known asteroids. They probably consist of clay and stony silicate rocks, and inhabit the main belt's outer regions. The S-type or silicaceous asteroids are greenish to reddish in color, account for about 17 percent of known asteroids, and dominate the inner asteroid belt. They appear to be made of silicate materials and nickel-iron. The M-type or metallic asteroids are reddish in color, make up most of the rest of the asteroids, and dwell in the middle region of the main belt. They seem to be made up of nickle-iron. There are many other rare types based on composition as well — for instance, V-type asteroids typified by Vesta have a basaltic, volcanic crust.
Earth impactsEver since Earth formed about 4.5 billion years ago, asteroids and comets have routinely slammed into the planet. The most dangerous asteroids are extremely rare, according to NASA.
An asteroid capable of global disaster would have to be more than a quarter-mile wide. Researchers have estimated that such an impact would raise enough dust into the atmosphere to effectively create a "nuclear winter," severely disrupting agriculture around the world. Asteroids that large strike Earth only once every 1,000 centuries on average, NASA officials say.
Smaller asteroids that are believed to strike Earth every 1,000 to 10,000 years could destroy a city or cause devastating tsunamis.
On Feb. 15, 2013, an asteroid slammed into the atmosphere over the Russian city of Chelyabinsk, creating a shock wave that injured 1,200 people. The space rock is thought to have measured about 65 feet (20 meters) wide when it entered Earth's atmosphere.
Dozens of asteroids have been classified as "potentially hazardous" by the scientists who track them. Some of these, whose orbits come close enough to Earth, could potentially be perturbed in the distant future and sent on a collision course with our planet. Scientists point out that if an asteroid is found to be on a collision course with Earth 30 or 40 years down the road, there is time to react. Though the technology would have to be developed, possibilities include exploding the object or diverting it. [Image Gallery: Potentially Dangerous Asteroids]
For every known asteroid, however, there are many that have not been spotted, and shorter reaction times could prove more threatening.
When an asteroid, or a part of it, crashes into Earth, it's called a meteorite. Here are typical compositions:
Iron meteorites:
- Iron 91 percent
- Nickel 8.5 percent
- Cobalt 0.6 percent
- Oxygen 36 percent
- Iron 26 percent
- Silicon 18 percent
- Magnesium 14 percent
- Aluminum 1.5 percent
- Nickel 1.4 percent
- Calcium 1.3 percent
NamingSince the International Astronomical Union is less strict on how asteroids are named when compared to other bodies, there are asteroids named after Mr. Spock of "Star Trek" and rock musician Frank Zappa as well as more solemn tributes, such as the seven asteroids named for the crew of the Space Shuttle Columbia killed in 2003. Naming asteroids after pets is no longer allowed.
Asteroids are also given numbers — for example, 99942 Apophis.
ExplorationThe first spacecraft to take close-up images of asteroids was NASA's Galileoin 1991, which also discovered the first moon to orbit an asteroid in 1994.
In 2001, after NASA's NEAR spacecraft intensely studied the near-earth asteroid Eros for more than a year from orbit, mission controllers decided to try and land the spacecraft. Although it wasn't designed for landing, NEAR successfully touched down, setting the record as the first to successfully land on an asteroid.
In 2006, Japan's Hayabusa became the first spacecraft to land on and take off from an asteroid. It returned to Earth in June 2010, and the samples it recovered are currently under study.
NASA's Dawn mission, launched in 2007, began exploring Vesta in 2011 and is slated to explore Ceres in 2015 and will be the first spacecraft to visit either body.
In 2012, a company called Planetary Resources, Inc. announced plans to eventually send a mission to a space rock to extract water and mine the asteroid for precious metals.
Meteors and Meteor Showers: The Science
Imagine a baseball zipping along at 30,000 miles per hour. That's how big and fast many meteors are. And though some are bigger than baseballs, most are more like grains of sand. The larger meteors are sometimes broken bits off asteroids or other planets. The small stuff is often dust left by a passing comet.
Entry into the atmosphere
When they plow through the atmosphere, meteors are heated to more than 3000 degrees Fahrenheit, and they glow. Meteors are not heated by friction, as is commonly thought. A phenomenon called ram pressure is at work. A meteor compresses air in front of it. The air heats up, in turn heating the meteor.
The intense heat vaporizes most meteors, creating what we call shooting stars. (Most become visible at around 60 miles up.) Some large meteors splatter, causing a brighter flash called a fireball, and an explosion, which can often be heard up to 30 miles away. When meteors hit the ground, they're calledmeteorites. Some meteors are bits broken off asteroids, others -- mere cosmic dust -- are cast off by comets. (And one more term: A meteoroid is an object in space that may, if it enters our atmosphere, become a meteor.)
Meteor breakup
Whether an object breaks apart depends on its composition, speed and angle of entry. A faster meteor at an oblique angle suffers greater stress. Meteors composed of iron withstand the stress better than those made of stone. Even an iron meteor will usually break up as the atmosphere becomes denser -- around 5 to 7 miles up.
A meteor sometimes explodes above the surface, causing widespread damage from the blast and ensuing fire. This happened in 1908 over Siberia.
Impact with Earth
Extraterrestrial objects that hit the ground, their speed roughly half what it was upon entry, blast out craters 12 to 20 times their size. Craters on Earth form much as they would on the moon or any rocky planet. Smaller objects create simple, bowl-shaped craters. Larger impacts cause a rebound that creates a central peak; slipping along the rim forms terraces. The largest impacts form basins in which multiple rebounds form several inner peaks.
Typical composition
Iron meteorite
Stony meteorite
Earth's crust
Iron 91%
Nickel 8.5%
Cobalt 0.6%
Source:
Encyclopaedia Britannica
Oxygen 36%
Iron 26%
Silicon 18%
Magnesium 14%
Aluminum 1.5%
Nickel 1.4%
Calcium 1.3%
Oxygen 49%
Silicon 26%
Aluminum 7.5%
Iron 4.7%
Calcium 3.4%
Sodium 2.6%
Potassium 2.4%
Magnesium 1.9%
History
In ancient times, objects in the night sky conjured superstition and were associated with gods and religion. But misunderstandings about meteors lasted longer than they did about most other celestial objects.
Meteorites (the pieces that make it to Earth) were long ago thought to be cast down as gifts from angels. Others thought the gods were displaying their anger. As late as the 17th century, many believed they fell from thunderstorms (they were nicknamed "thunderstones"). Many scientists were skeptical that stones could fall from the clouds or the heavens, and often they simply didn't believe the accounts of people who claimed to have seen such things.
In 1807, a fireball exploded over Connecticut, and several meteorites rained down. By then the first handful of asteroids had been discovered, and a new theory emerged suggesting meteorites were broken bits off asteroids or other planets. (A theory that still holds.)
One of the most significant meteorite events in recent history destroyed hundreds of square miles of forest in Siberia on June 30, 1908. Across hundreds of miles, witnesses of the Tunguska event saw a ball of fire streak through the sky, suggesting the meteor entered the atmosphere at an oblique angle. It exploded, sending out hot winds and loud noises and shook the ground enough to break windows in nearby villages. Small particles blown into the atmosphere lit the night sky for several days. No meteorite was ever found, and for years many scientists thought the devastation was caused by a comet. Now, the prevailing theory holds that a meteor exploded just above the surface.
The largest meteorite recovered in the United States fell in a wheat field in southern Nebraska in 1948. Witnesses saw a giant fireball in the afternoon that some said was brighter than the sun. The meteorite was found buried 10 feet deep in the ground. It weighed 2,360 pounds.
The most famous meteorite crater in the United States is misnamed Meteor Crater. It's in Arizona, and it's huge. The rim rises 150 feet from the surrounding plain, and the hole is 600 feet deep and nearly a mile wide. It was the first crater that was proved to be caused by a meteorite impact, which occurred between 20,000 and 50,000 years ago.
Meteor showers
When a comet nears the sun, a trail of dust and other debris burns off and remains in solar orbit. As Earth orbits the sun, it passes through this debris field spread across its path. Small bits burn up in the atmosphere, creating meteors. Meteors come from other sources, too, but comet debris streams are the source of sometimes dramatic meteor showers.
When to watch
The part of Earth where dawn is breaking is always at the leading edge of our planet's plunge along its orbital path around the Sun. This part of the planet tends to "catch" oncoming meteors left by a comet, whereas the other side of Earth, where it is dusk or late evening, outruns the debris. For that reason, the hours between midnight and dawn are typically the best time to watch a meteor shower.
Entry into the atmosphere
When they plow through the atmosphere, meteors are heated to more than 3000 degrees Fahrenheit, and they glow. Meteors are not heated by friction, as is commonly thought. A phenomenon called ram pressure is at work. A meteor compresses air in front of it. The air heats up, in turn heating the meteor.
The intense heat vaporizes most meteors, creating what we call shooting stars. (Most become visible at around 60 miles up.) Some large meteors splatter, causing a brighter flash called a fireball, and an explosion, which can often be heard up to 30 miles away. When meteors hit the ground, they're calledmeteorites. Some meteors are bits broken off asteroids, others -- mere cosmic dust -- are cast off by comets. (And one more term: A meteoroid is an object in space that may, if it enters our atmosphere, become a meteor.)
Meteor breakup
Whether an object breaks apart depends on its composition, speed and angle of entry. A faster meteor at an oblique angle suffers greater stress. Meteors composed of iron withstand the stress better than those made of stone. Even an iron meteor will usually break up as the atmosphere becomes denser -- around 5 to 7 miles up.
A meteor sometimes explodes above the surface, causing widespread damage from the blast and ensuing fire. This happened in 1908 over Siberia.
Impact with Earth
Extraterrestrial objects that hit the ground, their speed roughly half what it was upon entry, blast out craters 12 to 20 times their size. Craters on Earth form much as they would on the moon or any rocky planet. Smaller objects create simple, bowl-shaped craters. Larger impacts cause a rebound that creates a central peak; slipping along the rim forms terraces. The largest impacts form basins in which multiple rebounds form several inner peaks.
Typical composition
Iron meteorite
Stony meteorite
Earth's crust
Iron 91%
Nickel 8.5%
Cobalt 0.6%
Source:
Encyclopaedia Britannica
Oxygen 36%
Iron 26%
Silicon 18%
Magnesium 14%
Aluminum 1.5%
Nickel 1.4%
Calcium 1.3%
Oxygen 49%
Silicon 26%
Aluminum 7.5%
Iron 4.7%
Calcium 3.4%
Sodium 2.6%
Potassium 2.4%
Magnesium 1.9%
History
In ancient times, objects in the night sky conjured superstition and were associated with gods and religion. But misunderstandings about meteors lasted longer than they did about most other celestial objects.
Meteorites (the pieces that make it to Earth) were long ago thought to be cast down as gifts from angels. Others thought the gods were displaying their anger. As late as the 17th century, many believed they fell from thunderstorms (they were nicknamed "thunderstones"). Many scientists were skeptical that stones could fall from the clouds or the heavens, and often they simply didn't believe the accounts of people who claimed to have seen such things.
In 1807, a fireball exploded over Connecticut, and several meteorites rained down. By then the first handful of asteroids had been discovered, and a new theory emerged suggesting meteorites were broken bits off asteroids or other planets. (A theory that still holds.)
One of the most significant meteorite events in recent history destroyed hundreds of square miles of forest in Siberia on June 30, 1908. Across hundreds of miles, witnesses of the Tunguska event saw a ball of fire streak through the sky, suggesting the meteor entered the atmosphere at an oblique angle. It exploded, sending out hot winds and loud noises and shook the ground enough to break windows in nearby villages. Small particles blown into the atmosphere lit the night sky for several days. No meteorite was ever found, and for years many scientists thought the devastation was caused by a comet. Now, the prevailing theory holds that a meteor exploded just above the surface.
The largest meteorite recovered in the United States fell in a wheat field in southern Nebraska in 1948. Witnesses saw a giant fireball in the afternoon that some said was brighter than the sun. The meteorite was found buried 10 feet deep in the ground. It weighed 2,360 pounds.
The most famous meteorite crater in the United States is misnamed Meteor Crater. It's in Arizona, and it's huge. The rim rises 150 feet from the surrounding plain, and the hole is 600 feet deep and nearly a mile wide. It was the first crater that was proved to be caused by a meteorite impact, which occurred between 20,000 and 50,000 years ago.
Meteor showers
When a comet nears the sun, a trail of dust and other debris burns off and remains in solar orbit. As Earth orbits the sun, it passes through this debris field spread across its path. Small bits burn up in the atmosphere, creating meteors. Meteors come from other sources, too, but comet debris streams are the source of sometimes dramatic meteor showers.
When to watch
The part of Earth where dawn is breaking is always at the leading edge of our planet's plunge along its orbital path around the Sun. This part of the planet tends to "catch" oncoming meteors left by a comet, whereas the other side of Earth, where it is dusk or late evening, outruns the debris. For that reason, the hours between midnight and dawn are typically the best time to watch a meteor shower.
By : Harnoor Singh Div-4,Grade 6, Te scott elementary