Semi-planet Quaoar Content from the guide to life, the universe and everything

Semi-planet Quaoar

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The Solar System | Mercury | Venus | Earth | Mars | Ceres | Jupiter
Saturn | Chiron | Uranus | Neptune | Pluto
The Kuiper Belt and the Oort Cloud | Quaoar | Eris | Sedna

Like a rock the size of Texas, this world circles the Sun at a distance so great that any visitors would find it hard to tell which star it was attached to.

The International Astronomical Union would call this a KBO (Kuiper Belt Object) but with a diameter of 890km (550 miles) it is large enough to be considered more than just one of the billions of small chunks floating around in the Kuiper Belt. One source stated that there would fewer than ten objects beyond Neptune which were this large. Hubble Telescope observation tends to confirm that Quaoar is spherical and has a circular orbit around the Sun of 42 AU1 from the Sun. This contrasts with Pluto whose orbit varies from 29.5 to 48 AU. This contrast has been shown on a website at

The Discovery

Two scientists in California – Michael Brown and Chadwick Trujillo – were credited with the discovery in 2002 and thus had the honour of naming it. The name (pronounced 'Kwah-o-wahr') is from the Tongva Indian Tribe. These Native Americans considered Quaoar a Creation force. Further study showed that this object had been on photographic plates since 1982 but had not been studied previously. For some time, now there has been a search under way for a Tenth Planet which would be as large or larger than Pluto. As stated at the end of this article, it is doubtful whether such an object, even if found, would be considered a planet.


Quaoar's moon Weywot was discovered in February 2007 by M E Brown and T A Suer using the Hubble Space Telescope. The moon is five magnitudes dimmer than Quaoar and is roughly 74km in diameter. It rotates around Quaoar every 12.438 days at a distance of 14,500km. It was this knowledge that allowed an accurate estimate of the size and composition of Quaoar itself.

Also-rans in the Solar System

Another KBO also found in recent years was name Varuna. It is slightly smaller than Quaoar. Neither of these objects are likely to be called planets. Indeed, the IAU has now demoted Pluto to the status of dwarf planet.

The h2g2 Tour of the Solar System

Take the h2g2 Shuttle for your whistle-stop tour of the Solar System.

1One AU (Astronomical Unit) equals the distance between Earth and the Sun.

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