Derby and District Astronomical Society

The Journal of the Derby and District Astronomical Society
May - August 2006

Letters to the Editor

Dear Editor,

The last edition of Aries was excellent and informative. A couple of points. Dave Selfe suggests you might put some star maps in. Well, personally, I think that seeing as Aries is a quarterly magazine, it’d be difficult to do that. I notice, however, that you have included interesting events coming up, like the solar eclipse on the 29th March. Other events like what planets are on view, as well as visible comets, (none yet!}, etc, may also be worthy of mention.

I was particularly interested in the article on the New Horizons Explorer (written by Anthony Southwell - Editor) What an enigma Pluto has turned out to be. Anthony raised the hotly debated issue of Pluto’s planetary status. I have several reasons for believing Pluto to be a Kuiper Belt (KB) object, and these are discussed here.

Firstly, look at Pluto’s orbit! It’s at a high inclination compared to the rest of the planets. 2003 UB313, though larger than Pluto has an even higher inclination, reminiscent of a cometary orbit. Other KB objects have similar, highly inclined orbits. Secondly, many Kuiper Belt objects have been found to have companions, Pluto now seems to have three. Thirdly, Pluto is tiny. It’s smaller than our moon, and quite a few other satellites in the main solar system. 2003 UB313 may be larger, but it’s still on this scale of smallness. Sedna is another case in point. They are all small satellite sized objects.

Lastly, take a look at Triton, Neptune’s largest moon. Voyager had a good look at this world as it sped past Neptune in 1989. The latest data on Pluto seems to suggest that Pluto’s atmosphere and composition may be similar to this world. It’s likely that Triton is a captured KB object, and I wouldn’t be surprised if other KB objects turn out to be composed in a similar fashion, pointing to the generality of objects in the Kuiper Belt.

In conclusion, Pluto seems to have similar characteristics common to other KB objects, and that is why I believe it belongs firmly in that category. As to what did cause Neptune’s orbit to be perturbed leading to the hunt for Planet X s still unsolved, but neither Pluto nor 2003 UB 313 can be responsible, unless there is a fairly large body out there waiting to be discovered. It will be fascinating to see what New Horizons discovers in this area at the edge of the solar system. Maybe Anthony can give a talk on the findings when it arrives!

Claire Spencer

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