Den nye planet?

På den anden side af Plutos bane findes tusindvis af små "planeter/kometer" i det såkaldte Kuiper-bælte. For nyligt blev den hidtil største af disse - Quaoar - opdaget. Quaoar's tekniske navn er: 2002 LM60. Astronomerne regner med, at man i de kommende år vil finde endnu flere såkaldte KBO (Kuiper Belt Objects), og at flere af disse sikkert vil være større end Quaoar.

At tale om, at Quaoar er en ny planet, sådan som den i øjeblikket bliver lanceret i pressen, er derfor ikke så lidt af en tilsnigelse. Quaoar er - målt i forhold til de hidtil kendte planeter - umådelig lille og befinder sig umådeligt langt væk. Quaoar, er altså ikke en "rigtig" planet. Den består af is og klipper og har de samme kendetegn som kometer, men den er blot hundredtusindvis af gange større. Quaoar bevæger sig i et kredsløb 1,6 milliarder kilometer længere ude end Pluto og 10,8 milliarder kilometer fra Jorden.

Nedenfor ses Quaoars størrelsesforhold.

Christian Borup
Oktober 2002

Quaoar Ephemeris

Quaoar Ephemeride 1900-1924...
Quaoar Ephemeride 1925-1949...
Quaoar Ephemeride 1950-1974...
Quaoar Ephemeride 1975-1999...
Quaoar Ephemeride 2000-2024...
Quaoar Ephemeride 2025-2049...

Earlier this year, Trujillo and Brown used the Palomar Oschin Schmidt telescope to discover Quaoar as an 18.5-magnitude object creeping across the summer constellation Ophiuchus (it's less than 1/10,000th the brightness of the faintest star seen by the humaneye). Brown had to do follow-up observations using Hubble's new Advanced Camera for Surveys on July 5 and August 1, 2002, to measure the object's true angular size of 40 milliarcseconds, corresponding to a diameter of about 800 miles (1300 kilometers). Only Hubble has the sharpness needed to actually resolve the disk of the distant world, leading to the first-ever direct measurement of the true size of a Kuiper belt object (KBO).

Like Pluto, Quaoar dwells in the Kuiper belt, an icy debris field of comet-like bodies extending 7 billion miles beyond Neptune's orbit. Over the past decade more than 500 icy worlds have been found in the Kuiper belt. With a few exceptions all have been significantly smaller than Pluto.

Previous record holders are a KBO called Varuna, and an object called 2002 AW197, each approximately 540 miles across (900 kilometers). Unlike Hubble's direct observations, these diameters are deduced from measuring the objects' temperatures and calculating a size based on assumptions about the KBOs' reflectivity, so the uncertainty in true size is much greater.

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This latest large KBO is too new to have been officially named by the International Astronomical Union. Trujillo and Brown have proposed naming it after a creation god of the Tongva native American tribe, the original inhabitants of the Los Angeles basin. According to legend, 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."

Quaoar's "icy dwarf" cousin, Pluto, was discovered in 1930 in the course of a 15-year search for trans-Neptunian planets. It wasn't realized until much later that Pluto actually was the largest of the known Kuiper belt objects. The Kuiper belt wasn't theorized until 1950, after comet orbits provided telltale evidence of a vast nesting ground for comets just beyond Neptune. The first recognized Kuiper belt objects were not discovered until the early 1990s. This new object is by far the "biggest fish" astronomers have snagged in KBO surveys. Brown predicts that within a few years even larger KBOs will be found, and Hubble will be invaluable for follow-up observations to pin down sizes.

© Copyright 2002
Space Telescope Science Institite....

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De største KBO'er  før opdagelsen af "Quaoar" (2002 LM60)
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