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Posts Tagged ‘Kuiper Belt’

Yesterday (Thursday 21 January) I was on BBC Radio talking about the possibility of their being a 9th planet in the Solar System (remember, in 2006 Pluto was demoted to being a minor-planet, leaving us with 8). If this suggestion is true, this would lead to our once again having to revise the list of planets that many of us know knew by heart. It would not be the first time we have had to revise it, nor I suspect will it be the last.

The team’s argument is based on anomalies in the orbits of Kuiper belt objects. The Kuiper belt is a region beyond the orbit of Pluto which is the reservoir of short-period comets. I have blogged about the Kuiper belt before here. The authors of this new paper argue that some Kuiper belt objects are having their orbits disturbed by an unseen object, and they suggest that it is an object about ten times larger than Earth.

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The Caltech team claim that anomalies in the orbits of Kuiper belt objects suggest that there is a large planet disturbing them

It may come as a surprise to some of you that this is precisely the way that Neptune was discovered. After Uranus’ discovery by William Herschel in 1781, astronomers noticed that it was not orbiting exactly as it should. The simplest explanation was that its orbit was being affected by an unseen planet. Two mathematicians (Frenchman Urbain le Verrier and Englishman John Couch Adams) separately worked out where the disturbing object should be.  There was a race on for astronomers to find the object, and the race was won by astronomer Johann Galle in 1846 working at the Berlin Observatory.

The existence of this new 9th planet is a long way from being proven. The anomalies in the orbits of the Kuiper belt objects is an example of something called a ‘many-body problem’. The gravitational influence of many objects, including the Sun, Jupiter, the other gas giants, as well as other Kuiper belt objects, all have to be calculated to see if there are any unaccounted for effects. This is a horrendously complicated problem, and I am sure this prediction by this team from Caltech will be challenged by others working in this area of research. 

 

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Over the next few days we should be treated to the sight of one of the best comets in many years. Comet PANSTARRS is entering the inner part of the Solar System, and will be visible in the Western sky over the next week. Although we are not entirely sure, comet PANSTARRS should brighten over the next few days to become visible to the naked eye in the West just after sunset. The last good comet I saw was comet Hyakutake which was visible in 1997. Seeing a comet with its tail stretching across the sky is a memorable experience, so it is well worth making the effort over the next few days to try to see comet PANSTARRS.


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This image shows where we can expect to see the comet. For Northern Hemisphere observers it will be low in the Western sky just after Sunset.


This screen capture is taken from the website earthsky.org

This screen capture is taken from the website earthsky.org


Where do comets come from?

There are two basic types of comets, short period and long period comets. The short period comets come from the Kuiper Belt, which is a band of small objects just beyond the orbit of Pluto. In fact, Pluto is a Kuiper Belt object, and of course has been re-classified as a minor planet by the International Astronomical Union. The Kuiper Belt was postulated by Gerard Kuiper in 1951, but the first Kuiper Belt object (apart from Pluto) was not discovered until 1992. The Kuiper belt lies at between 50 and 100 Astronomical Units (AUs), where 1 AU is the distance from the Earth to the Sun.


The Kuiper belt lies beyond the orbit of Pluto, and is the reservoir of short period comets.

The Kuiper belt lies beyond the orbit of Pluto, and is the reservoir of short period comets.


Long period comets come from much further out in the Solar System, they come from the Oort Cloud. The Oort cloud is about 2,000 times further away than the Kuiper Belt, lying at about 100,000 AUs. The Oort cloud is so far away that we will probably never directly observe objects in the Oort cloud.


The Oort cloud is the reservoir of long period comets, lying about 2,000 times further away than the Kuiper Belt.

The Oort cloud is the reservoir of long period comets, lying about 2,000 times further away than the Kuiper Belt.


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