cubewano and first discovered Kuiper belt object

Note: Diameters marked as approximate (~) may have errors as large as 125 miles (200 km).

Jack Wisdom at the Massachusetts Institute of Technology, and their colleagues show that Kuiper belt bodies can survive for the age of the solar system in a selection of their current, stable orbits. This study implies that Kuiper belt bodies are the remnants of the solar nebula that have stayed frozen and unaltered in the outer solar system for the last 4.56 billion years. Observations of the Kuiper belt, then, are literally observations of the original solar nebula itself.

David Jewitt and his colleagues discovered one of the first very large Kuiper belt bodies, 20000 Varuna, in November 2000 using the Spacewatch telescope in Arizona. Originally known as 2000 WR106, Varuna is thought to be about 620 miles (1,000 km) in diameter. Its diameter is therefore less than half Pluto's. It is still larger than 1 Ceres, which is 577 by 596 miles (930 by 960 km) in diameter. Until Varuna was found, researchers thought that all Kuiper belt objects might have albedos of about 4 percent (with the exception of brilliantly bright Pluto). Varuna, though, seems to have an albedo of about 7 percent. Its brightness worked to energize the science community a little bit, since the brighter the objects are, the easier they are to find, and so more searches for Kuiper belt objects might be successful. Initially Varuna was thought to be as large as Charon, but with more refined calculations of its albedo the discovery team announced that it was in fact significantly smaller. Still, it was and is one of the larger objects yet discovered. Since Varuna, there have been at least four Kuiper belt objects discovered that are larger.

In July 2001, Robert Millis and his colleagues at the Massachusetts Institute of Technology, Lowell Observatory, and the Large Binocular Telescope Observatory in Arizona discovered 28978 Ixion (originally 2001 KX ), a large Kuiper belt object (most of these people were also on the team that discovered Uranus's rings in 1977). Along with Varuna, Ixion is larger than 1 Ceres. Ixion's size was highly uncertain when it was discovered because the telescope through which it was discovered had neither the high resolution required to measure size directly (the Hubble Space Telescope can do this) nor the ability to measure infrared radiation, which is related to size. At the time of discovery, the team thought Ixion was at least 750 miles (1,200 km) in diameter. This estimated size made a big media splash, since at the time it would have been the largest Kuiper belt object after Pluto, and in fact larger than Charon itself. Further study

Comparison of Pluto, Charon, Sedna, Etc.

Pluto radius: 748 miles (1.195 km)


Varuna radius: -310 miles (-500 km)

Mercury radius: 1,515 miles (2,440 km)

Earth's Moon radius: 1,079.6 miles (1,737.4 km)

Sedna First observed Oort cloud object?

Ceres Largest asteroid in the main belt

Kuiper belt objects are labeled at the top; other objects at the bottom. Bodies in italic may have errors in their diameters as large as 125 miles (200 km)

shows Ixion to be only about 580 miles (930 km) in diameter, and in the intervening years a number of larger Kuiper belt bodies have been discovered, including two that really may be larger than Charon.

In June 2002, California Institute of Technology scientists Chad Trujillo (now at the Gemini Observatory) and Mike Brown saw for the first time a Kuiper belt body with the preliminary name 2002 LM60, later named 50000 Quaoar (pronounced KWAH-o-wahr). Quaoar is named for the god found in the creation stories of the Tongva tribe, early inhabitants of southern California. Quaoar lies at about 42 AU from the Sun. Its orbit takes about 285 Earth years and is almost circular, with an eccentricity of only 0.04 and an inclination of about 8°. Pluto's orbital eccentricity is about six times larger than that of Quaoar's, and Pluto's inclination is about twice Quaoar's. Because Quaoar is so bright, within a month of discovery they were able to trace its position back two decades in previously taken telescope images. Quaoar has a diameter of 780 miles (1,250 km), about half the size of Pluto. Quaoar was at the time of its discovery the largest solar system body found since Pluto itself.

A comparison of the sizes of Mercury, the Moon, Pluto, and a series of minor planets shows that all known Kuiper and asteroid belt objects are smaller than Pluto, but even Pluto is smaller than Earth's Moon.

In February 2004, Brown, Trujillo, and their colleague David Rabinowitz from Yale University had a new announcement about the largest known Kuiper belt object, having found a new object designated 2004 DW that is still larger than Quaoar. Based on its current distance of about 48 AU from the Sun, its brightness, and its presumed albedo, 2004 DW has been estimated to be around 870—990 miles (1,400—1,600 km) in diameter, or more than half the size of Pluto. As with many other found objects, once they are identified they can then be found in photographs from sky surveys in the past. 2004 DW has been found in a First Palomar Sky Survey photograph of November 23, 1954, and in a November 8, 1951, photograph from the Siding Spring Observatory in Australia. 2004 DW appears to be a plutino with an orbit that carries it from 30.9 and 48.1 AU with an orbital inclination of about 20.6°. 2004 DW requires 248 years to complete its orbit. It reached aphelion in 1989 and will reach perihelion in 2113.

Trujillo and Brown expect to find five to 10 more large objects and perhaps some larger than Pluto.They search using a sequence of highresolution telescope images of the same region in space, looking for objects that move relative to the starry background (the stars are moving, also, but they are so far away relative to Kuiper belt objects that their movement is undetectable over short periods of time).They spent about seven months looking using the Oschin Telescope at Palomar, California. It has a mirror diameter of 1.2 meters, which is large compared to amateur telescopes (typically ranging from 0.1 to 0.3 meters in diameter), but small compared to most professional telescopes (one to 10 meters in diameter). Although the mirror is not very large, the Oschin Telescope has a huge field of view for its size, about (3.75°)2.That is about the same amount of sky area as 12 moons in each picture.

Though Jewitt and others think Kuiper belt objects as large or larger than Pluto may remain undiscovered in the outer Kuiper belt, it is unlikely that any really large Kuiper belt object exists. Any large body in the outer solar system would have perturbed the paths of the spacecraft Voyager 1,Voyager 2, and Pioneer 10 as they passed the solar system and should further influence the orbit of comet Halley.To have avoided changing the orbits of these objects any remaining large Kuiper belt objects are thought to be less than five Earth masses, which in its turn is far larger than the estimated total mass of the

Kuiper belt. According to Kuiper's original calculations as well as computer simulations of losses to the inner solar system and gravitational expulsions into outer space, the Kuiper belt's original mass in the beginning of the solar system was the equivalent of about 30 Earth masses. Now it is 0.2 Earth masses, or about 100 times the mass of the asteroid belt.

The accompanying figure demonstrates the loss of mass from the inner solar system, particularly from the asteroid belt. The mass of matter at a given orbit divided by the area of the orbit is plotted on the vertical axis as a measure of density of material existing at that jhe density of material in the distance from the Sun.The horizontal axis measures distance from the solar system decreases with Sun in AU. Theories and models of the solar nebula clearly indicate distance from the Sun.

Density of Solar System with Distance from the Sun

1012 (1011)

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