Image Credit: Greg Bacon/STSci and NASA/MODIS.
Large Icy Bodies and particles down to the size of dust reside beyond Jupiter in the Kuiper Belt, a disk of debris left over from the formation of the solar system.
Here are some facts and other places you can find information about these Kuiper Belt Objects.
The artist's impression (above) is the icy Kuiper Belt object 2002 LM60, dubbed "Quaoar" (pronounced kwa-whar) by its discoverers, Michael Brown and Chadwick Trujillo of Caltech. Quaoar is the creation god of the Native American Tongva tribe, the original inhabitants of the Los Angeles area where Caltech is located. According to the tribe's creation story, Quaoar "came down from heaven; and, after reducing chaos to order, laid out the world on the back of seven giants. He then created the lower animals and, then, mankind."
At left is a comparison of the object to North America. NASA's
Hubble Space Telescope has measured Quaoar and found it to be about 800 miles (1300 kilometers) in diameter which is about half the size of Pluto. Like
Pluto, Quaoar dwells in the Kuiper Belt, an icy debris field of comet-like objects reaching 7 billion miles beyond Neptune's orbit. Over the past ten years more than 500 icy bodies, Kuiper-Belt Objects or "KBOs", have been found there. Quaoar is about 4 billion miles (6.5 billion kilometers) from Earth, more than 1 billion miles farther than Pluto.
Click on image for a detail view.
The icy body is about 400 km wider than the biggest main-belt asteroid (Ceres) and the largest object in the solar system found since the discovery of Pluto in 1930. Other large bodies are a KBO called Varuna, and an object called 2002 AW197, each is about 540 miles across (900 kilometers). The image at right compares the size of Quaoar to Pluto, the Moon, and Earth. Click on image for a detail view.
Quaoar is bigger than all known asteroids combined and astronomers think it's made mostly of low-density ices mixed with rock, similar to a comet. Kuiper Belt Objects have very low mass compared to rocky bodies like asteroids and many get pushed out of their orbits to become short-period comets, those that orbit the sun in less than 200 years. Comets that take longer than 200 years or long-period comets usually come from the Oort Cloud. This huge spherical cloud that surrounds the solar system is left over from the formation of the system. Quaoar's nearly circular orbit around the Sun takes 288 years.
What is a Planet?
The International Astronomical Union recently decided on a definition of the word "planet". The IAU members gathered at the 2006 General Assembly agreed that a "planet" is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and (c) has cleared the neighborhood around its orbit.
This means that the Solar System consists of eight "planets" Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called "dwarf planets" was also decided. It was agreed that "planets" and "dwarf planets" are two distinct classes of objects. The first members of the dwarf planet category are Ceres, Pluto and 2003 UB313, given the name Eris. More dwarf planets are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate dwarf planets are listed on IAU's dwarf planet watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.
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