What is the asteroid belt?The vast majority of asteroids in the solar system are found in a region of the solar system out beyond Mars. They form the Asteroid Belt. Others orbit in near-Earth space and a few migrate or are thrown out to the outer solar system by gravitational interactions. The four largest asteroids in the belt are Ceres, Vesta, Pallas, and Hygiea. They contain half the mass of the entire belt. The rest of the mass is contained in countless smaller bodies. There was a theory once that if you combined all the asteroids they would make up the missing “Fifth” rocky planet. Planetary scientists estimate that if you could put all that material together that exists there today, it would make a tiny world smaller than Earth’s moon.
Where is the asteroid belt located? The Asteroid Belt is located in an area of space between the orbits of Mars and Jupiter. That places it between 2.2 and 3.2 astronomical units (AU) from the Sun. The belt is about 1 AU thick. The average distance between objects in the Asteroid Belt is quite large. If you could stand on an asteroid and look around, the next one would be too far away to see very well.
Asteroid Mining. The solar system contains many different types of asteroids, grouped by the minerals they contain. The abundances of precious metals such as nickel, iron, and titanium (to name a few), and water make asteroids an attractive target for mining operations when humans decide to expand their presence through interplanetary space. For example, water from asteroids could serve colonies in space, while the minerals and metals would be used to build habitats and grow food for future space colony inhabitants. Beginning 2013, companies interested in asteroid mining began announcing their plans for future operations on distant planetoids. In addition, NASA is looking into similar missions. The biggest obstacles to asteroid mining are the need to develop affordable spaceflight technology that would allow humans to get to the asteroids of interest.
Asteroid Belt objects are made of rock and stone. Some are solid objects, while others are orbiting “rubble piles”.
The Asteroid Belt contains billions and billions of asteroids.
Some asteroids in the Belt are quite large, but most range in size down to pebbles.
The asteroid 1/Ceres is also designated as a dwarf planet, the largest one in the inner solar system.
We know of at least 7,000 asteroids.
The Asteroid Belt may contain many objects, but they are spread out over a huge area of space. This has allowed spacecraft to move through this region without hitting anything.
Asteroids get their names from suggestions by their discoverers and are also given a number.
The formation of Jupiter disrupted the formation of any worlds in the Asteroid Belt region by scattering asteroids away. This caused them to collide and break into smaller pieces.
Gravitational influences can move asteroids out of the Belt.
Orbits of inner planets are shown as large circles in this computer-generated snapshot of actual known objects as of July 20, 2002. Green dots represent asteroids in the main belt between Mars and Jupiter. Red dots are asteroids that stray out of the main belt and pose a small but known possible risk of hitting Earth.
Scattered in orbits around the sun are bits and pieces of rock left over from the dawn of the solar system. Most of these objects, called planetoids or asteroids — meaning "star-like" — orbit between Mars and Jupiter in a grouping known as the Main Asteroid Belt.
The Main Asteroid Belt lies more than two-and-a-half times as far as Earth does from the sun. It contains millions of asteroids, according to NASA. Most of these are relatively small, from the size of boulders to a few thousand feet in diameter. But some are significantly larger.
Early in the life of thesolar system, dust and rock circling the sun were pulled together by gravity into planets. But not all of the ingredients created new worlds. A region between Mars and Jupiter became the asteroid belt.
Occasionally people wonder whether the belt was made up of the remains of a destroyed planet, or a world that didn't quite get started. However, according to NASA, the total mass of the belt is less than the moon, far too small to weigh in as a planet. Instead, the debris is shepherded by Jupiter, which kept it from coalescing onto other growing planets.
Observations of other planets are helping scientists to better understand the solar system. According to a developing theory known as Grand Tack, in the first 5 million years of the solar system, Jupiter and Saturn are thought to have moved inward toward the sun before changing direction and heading back to the outer solar system. Along the way, they would have scattered the original asteroid belt before them, then sent material flying back to refill it.
"In the Grand Tack model, the asteroid belt was purged at a very early stage and the surviving members sample a much larger region of the solar nebula," John Chambers of the Carnegie Institution for Science wrote in a "Perspectives" piece published online in the journal SCIENCE.
Our solar system isn't the only one to boast an asteroid belt. A cloud of dust around a star known as Zeta Leporis looks a lot like a young belt. "Zeta Leporis is a relatively young star — approximately the age of our sun when the Earth was forming," Michael Jura said in a statement. "The system we observed around Zeta Leporis is similar to what we think occurred in the early years of our own solar system when planets and asteroids were created." A professor at the University of California, Los Angeles; Jura has since passed away.
Other stars also contain signs of asteroid belts, suggesting that may be common.
At the same time, studies of white dwarfs, sun-like stars at the end of their lifetimes, show signatures of rocky material falling onto their surface that suggest such belts are common around dying systems.
Most of the asteroids in the Main Belt are made of rock and stone, but a small portion of them contain iron and nickel metals. The remaining asteroids are made up of a mix of these, along with carbon-rich materials. Some of the more distant asteroids tend to contain more ices. Although they aren't large enough to maintain an atmosphere, but there is evidence that some asteroids contain water.
Some asteroids are large, solid bodies — there are more than 16 in the belt with a diameter greater than 150 miles (240 km). The largest asteroids, Vesta, Pallas, and Hygiea, are 250 miles (400 km) long and bigger. The region also contains the dwarf planet Ceres. At 590 miles (950 km) in diameter, or about a quarter of the size of our moon, Ceres is round yet is considered too small to be a full-fledged planet. However, it makes up approximately a third of the mass of the asteroid belt.
Other asteroids are piles of rubble held together by gravity. Most asteroids aren't quite massive enough to have achieved a spherical shape and instead are irregular, often resembling a lumpy potato. The asteroid 216 Kleopatra resembles a dog bone.
Asteroids are classified into several types based on their chemical composition and their reflectivity, or albedo.
C-type asteroids make up more than 75 percent of known asteroids. The "C" stands for carbon, and the surfaces of these extremely dark asteroids are almost coal-black. Carbonaceous chondrite meteorites on Earth have a similar composition, and are thought to be pieces smashed off of the larger asteroids. While C-type asteroids dominate in the belt, according to the European Space Agency (ESA), they make up only about 40 percent of the asteroids closer to the sun. These include subgroups of B-type, F-type, and G-types.
S-type asteroids are the second most common type, making up about 17 percent of known asteroids. They dominate the inner asteroid belt, becoming rarer farther out. They are brighter and have metallic nickel-iron mixed with iron- and magnesium-silicates. The "S" stands for silicaceous.
M-type asteroids ("M" for metallic) are the last major type. These asteroids are fairly bright and most of them are composed of pure nickel-iron. They tend to be found in the middle region of the asteroid belt.
The remaining rare types of asteroids are A-type, D-type, E-type, P-type, Q-type, and R-type.
In 2007, NASA launched a mission, Dawn, to visit Ceres and Vesta. Dawn reached Vesta in 2011 and remained there for over a year before traveling on to reach Ceres in 2015. It will remain in orbit around the dwarf planet until the end of its mission. While most of the asteroid belt is made up of rocky objects, Ceres is an icy body. Hints of organic material spotted by Dawn suggest that it may have formed farther out in the solar system before landing in the belt. While the organics have only been seen on the surface, that doesn't mean more material might lie on the dwarf planet.
"We cannot exclude that there are other locations rich in organics not sampled by the survey, or below the detection limit," Maria Cristina De Sanctis, of the Institute for Space Astrophysics and Space Planetology in Rome, told Sapce.com via email.
Building a belt
The Main Belt lies between Mars and Jupiter, roughly two to four times the Earth-sun distance, and spans a region about 140 million miles across. Objects in the belt are divided into eight subgroups named after the main asteroids in each group. These groups are the Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas.
Although Hollywood often displays ships making close calls through asteroid belts, the trip is generally uneventful. A number of spacecraft have safely traveled through the asteroid belt without incident, including NASA's New Horizons mission to Pluto. "Fortunately, the asteroid belt is so huge that, despite its large population of small bodies, the chance of running into one is almost vanishingly small — far less than one in a billion," wrote New Horizons principle investigator Alan Stern. "If you want to come close enough to an asteroid to make detailed studies of it, you have to aim for one." Within in the asteroid belt are relatively empty regions known as Kirkwood gaps. These gaps correspond to orbital resonances with Jupiter. The gas giant's gravitational pull keeps these regions far emptier than the rest of the belt. In other resonances, the asteroids can be more concentrated.
Discovery of the asteroid belt
Johann Titius, an 18th-century German astronomer, noted a mathematical pattern in the layout of the planets and used it to predict the existence of one between Mars and Jupiter. Astronomers scoured the heavens in search of this missing body. In 1800, 25 astronomers formed a group known as the Celestial Police, each searching 15 degrees of the Zodiac for the missing planet. But the discovery of the first body in this region came from a nonmember, Italian astronomer Giuseppe Piazzi: he named it Ceres. A second body, Pallas, was found a little over a year later.
Located in the Asteroid Belt between the orbits of Mars and Jupiter, Ceres is the closest dwarf planet to the Sun and the only one located in the inner solar system. It's the smallest of the known dwarf planets at 950 km (590 mi) in diameter.
Ceres was the first object to be considered an asteroid in the solar system. In early 1801, an Italian astronomer by the name of Giuseppe Piazzi discovered and named Ceres. He originally classified it as a planet, but it has since been reclassified as a dwarf planet.
Ceres accounts for approximately one third of the mass of the entire asteroid belt but it cannot be classified as planet since it does not “dominate its orbit” – sharing it instead with many thousands of asteroids.
The unmanned spacecraft Dawn arrived at Ceres in early 2015. This probe was launched by NASA on 27th September, 2007 and should it complete it complete its mission, it will be the only craft to successfully orbit two separate extraterrestrial bodies – having completed a fourteen-month survey mission of the protoplanet Vesta in late 2012.
Ceres was named for the Roman God of agriculture, Ceres (or Cerere in Italian) – also known as Demeter in Greek mythology. The original name of Cerere Ferdinandea was changed after there were objections to Ferdinandea.
Ceres was classified as a planet for half a century – from 1801 until the 1850s – when it was reclassified as an asteroid. In 2006, it was subsequently classified as a dwarf planet.
The presence of water ice on Ceres has led to speculation that life may exist there. Discussions about life on Ceres are not as active as those for Mars or Europa, however.
Ceres is believed to have a rocky core with an icy inner mantle that is 100km thick. Scientists have calculated that this ice mantle may contain as much as 200 million cubic kilometers of water – that’s more fresh water than can be found on planet Earth.
Ceres is generally regarded as too dim to be seen with the naked eye but a viewer with exceptional eyesight under the right conditions might be able to see the dwarf planet.
Part of NASA’s Discovery Program, Dawn was a mission to the two most massive bodies in the main asteroid belt – Vesta and Ceres. These diverse worlds offer scientific snapshots of the early solar system. Vesta is rocky, while dwarf planet Ceres is icy. Each followed a very different evolutionary path, constrained by the diversity of processes that operated during the first few million years of the solar system. When Dawn visited Ceres and Vesta, the spacecraft brought us back in solar system time.
By using the same instruments to study diverse destinations, Dawn revealed new insight into the early solar system. A mission in NASA's Discovery Program, Dawn orbited and explored the protoplanet Vesta in 2011-2012, and it has been in orbit around a second new world, dwarf planet Ceres, since March 2015. Propelled by an efficient ion engine, Dawn delved into the unknown and achieved what's never been attempted before: it is the first mission to orbit an object in the main asteroid belt, the first to visit a dwarf planet, and the first to orbit two deep-space destinations.
On Nov. 1, 2018, Dawn ended its mission. Currently, it’s in orbit around Ceres, where it will remain for decades. (c) NASA