The Asteroid Belt:
The asteroid belt lies between the orbit or Mars (the last of the rocky planets) and the orbit of Jupiter (the largest planet in our solar system).
This picture, while not entirely accurate, helps to put into perspective just how much space the belt occupies. Unlike the picture, the true distances between the asteroids is thousands of miles. If you were to be in a ship going through the asteroid belt (much like Voyager 1 and 2), the closest asteroids would appear to be stars in the distance. Major collisions between asteroids therefore only occur about once every 10 million years; not much time in the astronomical sense, but odds are humans have never existed while one occurred.
The bulk of the asteroids in the main asteroid belt are silicate based rocks, similar to rocks found on the Earth. The rest of the asteroids are made mostly of iron and ice. In addition to the main asteroid belt, there are two large clumps of asteroids known as the Trojan asteroids. These are made almost entirely of water ice and rocks and are shepherded along by the enormous gravitational forces of Jupiter.
Scientists are greatly divided as to the origins of these clumps of asteroids. NASA believes there are two most likely scenarios as to their origin. The first is that during the early life of the Solar System, a time described as full of collisions and generally chaotic, a planet sized body was hit by a larger body and obliterated. The leftover pieces were than gravitationally trapped in orbit around the Sun and have so far failed to accrete into one large body. The second theory is that these asteroids were never a large body at all, but were simply remnants of the early Solar system that were never able to accrete into a large body. The first theory, also the first to be developed, has fallen out of favor within the scientific community. This is because, surprising as it might seem, the total mass of the asteroid belt is only 4% the mass of our own Moon. Also, the energy required to completely obliterate an object of that size is very large, casting further doubt on the first hypothesis. The second is the generally accepted theory today.
My truly favorite thing about the asteroid belt is that it contains one of the five recognized dwarf planets in our solar system.
Brief Aside!
In 2006, The IAU (International Astronomical Union) decided that the definition of what a true planet was needed to be set. This was the decision that killed Pluto as a "planet." Now, despite what was reported by many news outlets, Pluto was not kicked out of the solar system, it was simply redefined as a dwarf planet. This decision, while it might seem a bit arbitrary, actually makes a great deal of sense:
Planet: A large spherical body that orbits a star. To be classified as a true planet, it must follow a distinct orbital path and clear its path of other objects that are not gravitationally bound to it. True planets, as far as scientists have been able to determine, need to have a diameter of over 3,030 miles in order to generate the required gravitational force.
Dwarf Planet: A smaller spherical body that orbits a star, almost always (and completely in the case of our solar system) having a diameter of less than 3,030 miles. This is because dwarf planets do not have the mass to have a strict orbital path and they do not have the gravitational force to displace objects in their orbital paths, besides objects that are gravitationally bound to them.
To be designated as any kind of planet, the object needs to have enough mass to have gravitationally collapsed into a spherical shape and must be orbiting a star. For example, Jupiter's moon Ganymede is larger than the planet Mercury but because it orbits Jupiter, it is classified as a satellite, not a planet.
Back to the blog!
Now that we have those definitions out of the way, I can tell you guys about the dwarf planet Ceres.
Understandably, you might be thinking that the whole Planet vs. Dwarf planet is a bit unnecessary. However when you compare Ceres to the size of the Earth and even our Moon, you can see just how small it actually is.
Ceres has a diameter of just 590 miles, 13 times smaller than Earth's. It is a rocky, icy body and, due to its size, was the first asteroid discovered. Although at the time, scientists were not aware of the presence of the rest of the asteroids and thus classified it as a planet. While Ceres is very small in terms of the Earth, it contains 25% of the total mass of the asteroid belt. Meaning that the total mass of the asteroid belt is less than that of our own Moon. Dwarf planet now seems to be a fitting description for Ceres.
In addition to Ceres, there is another object in the asteroid belt that is of particular interest to the astronomical community; the rocky body 4 Vesta.
4 Vesta, as you can see from the image has a kind of squat potato shape. It has an average diameter of about 330 miles making it the second most massive asteroid in the asteroid belt. Scientists have taken particular interest in 4 Vesta because they believe that it might be about as small as a body can get before it gravitationally collapses into a spherical shape. As a result of this observation, in 2007 scientists sent the Dawn spacecraft on a mission to 4 Vesta and Ceres. The Dawn spacecraft has been orbiting 4 Vesta since July of 2011 and has provided us with very detailed pictures of its surface.
After Dawn's 4 Vesta mission is over, it will continue on to Ceres, arriving there in 2015. This mission is coinciding with a mission to Pluto, so we will have much more detailed images of Ceres and Pluto in the very near future.
Despite the scientific interest, 4 Vesta is not a dwarf planet. As you can see from the above image, 4 Vesta is not spherical in shape, even though it isn't that much smaller than Ceres.
The asteroid belt provides us with valuable information as to the formation of our early solar system and about rocky bodies of all sizes within space. When 2015 rolls around, our understanding of the asteroid belt and the bodies contained within it, will only be expanded from here on out.
Thanks for reading! The next blog will be on the planet Jupiter.
*Update!*
As of today (5/10/12) Vesta 4 has been upgraded from an asteroid to a protoplanet. Meaning, it will eventually become a dwarf planet, once it gains more mass. This new distinction is because of the Dawn spacecraft's current mission orbiting Vesta.
This picture, while not entirely accurate, helps to put into perspective just how much space the belt occupies. Unlike the picture, the true distances between the asteroids is thousands of miles. If you were to be in a ship going through the asteroid belt (much like Voyager 1 and 2), the closest asteroids would appear to be stars in the distance. Major collisions between asteroids therefore only occur about once every 10 million years; not much time in the astronomical sense, but odds are humans have never existed while one occurred.
The bulk of the asteroids in the main asteroid belt are silicate based rocks, similar to rocks found on the Earth. The rest of the asteroids are made mostly of iron and ice. In addition to the main asteroid belt, there are two large clumps of asteroids known as the Trojan asteroids. These are made almost entirely of water ice and rocks and are shepherded along by the enormous gravitational forces of Jupiter.
Scientists are greatly divided as to the origins of these clumps of asteroids. NASA believes there are two most likely scenarios as to their origin. The first is that during the early life of the Solar System, a time described as full of collisions and generally chaotic, a planet sized body was hit by a larger body and obliterated. The leftover pieces were than gravitationally trapped in orbit around the Sun and have so far failed to accrete into one large body. The second theory is that these asteroids were never a large body at all, but were simply remnants of the early Solar system that were never able to accrete into a large body. The first theory, also the first to be developed, has fallen out of favor within the scientific community. This is because, surprising as it might seem, the total mass of the asteroid belt is only 4% the mass of our own Moon. Also, the energy required to completely obliterate an object of that size is very large, casting further doubt on the first hypothesis. The second is the generally accepted theory today.
My truly favorite thing about the asteroid belt is that it contains one of the five recognized dwarf planets in our solar system.
Brief Aside!
In 2006, The IAU (International Astronomical Union) decided that the definition of what a true planet was needed to be set. This was the decision that killed Pluto as a "planet." Now, despite what was reported by many news outlets, Pluto was not kicked out of the solar system, it was simply redefined as a dwarf planet. This decision, while it might seem a bit arbitrary, actually makes a great deal of sense:
Planet: A large spherical body that orbits a star. To be classified as a true planet, it must follow a distinct orbital path and clear its path of other objects that are not gravitationally bound to it. True planets, as far as scientists have been able to determine, need to have a diameter of over 3,030 miles in order to generate the required gravitational force.
Dwarf Planet: A smaller spherical body that orbits a star, almost always (and completely in the case of our solar system) having a diameter of less than 3,030 miles. This is because dwarf planets do not have the mass to have a strict orbital path and they do not have the gravitational force to displace objects in their orbital paths, besides objects that are gravitationally bound to them.
To be designated as any kind of planet, the object needs to have enough mass to have gravitationally collapsed into a spherical shape and must be orbiting a star. For example, Jupiter's moon Ganymede is larger than the planet Mercury but because it orbits Jupiter, it is classified as a satellite, not a planet.
Back to the blog!
Now that we have those definitions out of the way, I can tell you guys about the dwarf planet Ceres.
This is an actual image of Ceres taken by the Hubble Space Telescope.
Understandably, you might be thinking that the whole Planet vs. Dwarf planet is a bit unnecessary. However when you compare Ceres to the size of the Earth and even our Moon, you can see just how small it actually is.
You can see that our own Moon dwarfs Ceres in size. However, our Moon, even though it is larger than Ceres, is classified as a moon because it orbits a planet and not the Sun.
Ceres has a diameter of just 590 miles, 13 times smaller than Earth's. It is a rocky, icy body and, due to its size, was the first asteroid discovered. Although at the time, scientists were not aware of the presence of the rest of the asteroids and thus classified it as a planet. While Ceres is very small in terms of the Earth, it contains 25% of the total mass of the asteroid belt. Meaning that the total mass of the asteroid belt is less than that of our own Moon. Dwarf planet now seems to be a fitting description for Ceres.
In addition to Ceres, there is another object in the asteroid belt that is of particular interest to the astronomical community; the rocky body 4 Vesta.
An image of Vesta provided to us again by the Hubble Space Telescope.
4 Vesta, as you can see from the image has a kind of squat potato shape. It has an average diameter of about 330 miles making it the second most massive asteroid in the asteroid belt. Scientists have taken particular interest in 4 Vesta because they believe that it might be about as small as a body can get before it gravitationally collapses into a spherical shape. As a result of this observation, in 2007 scientists sent the Dawn spacecraft on a mission to 4 Vesta and Ceres. The Dawn spacecraft has been orbiting 4 Vesta since July of 2011 and has provided us with very detailed pictures of its surface.
4 Vesta, as imaged by the Dawn spacecraft.
After Dawn's 4 Vesta mission is over, it will continue on to Ceres, arriving there in 2015. This mission is coinciding with a mission to Pluto, so we will have much more detailed images of Ceres and Pluto in the very near future.
Despite the scientific interest, 4 Vesta is not a dwarf planet. As you can see from the above image, 4 Vesta is not spherical in shape, even though it isn't that much smaller than Ceres.
The asteroid belt provides us with valuable information as to the formation of our early solar system and about rocky bodies of all sizes within space. When 2015 rolls around, our understanding of the asteroid belt and the bodies contained within it, will only be expanded from here on out.
Thanks for reading! The next blog will be on the planet Jupiter.
*Update!*
As of today (5/10/12) Vesta 4 has been upgraded from an asteroid to a protoplanet. Meaning, it will eventually become a dwarf planet, once it gains more mass. This new distinction is because of the Dawn spacecraft's current mission orbiting Vesta.
