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Name: Grant W Gearhart, Kathy Tice, B Randolph, Steve Mueller and   
               Pamela A McDermott
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Question:
I would like a little information on Planet X. I would like to know where it is located.



Replies:
Planet X was postulated to exist beyond the orbit of Pluto to account for apparent gravitational perturbations in the orbits of Neptune and Uranus. It was these perturbations that led to the search for Pluto, but after Pluto was found it was determined that its mass is not sufficient to fully account for those perturbations. Despite many years of searching, no planet X has been found. Nowadays most astronomers do not believe that Planet X exists; the apparent perturbations, they believe, are due simply to errors in observational data.

RC Winther


Many scientists once thought that there must be a planet beyond Neptune and Uranus to account for a variation in their orbits. Once Pluto was discov- ered, its mass was not large enough to account for this variation. As observations have gotten better with the help of things like the Voyagers, scientists now think that those unexplained variations were really observa- tional error.

This is a really good example of the process of science: always willing to question, apply new data, make new hypotheses...

E Mayo


As a historical note, the term "Planet X" was coined by the astronomer Percival Lowell in 1915. It referred to a hypothetical planet beyond Neptune that would account for the (apparent) gravitational perturbations in the orbits of Uranus and Neptune not due to the other known planets. Clyde Tombaugh discovered Pluto in 1930, but it was found that Pluto was not nearly massive enough to produce the perturbations. So Pluto was not Planet X, and the search continued, without success. In recent years, with the benefit of more and better data (including measurements by the Voyager probes) most astronomers have come to believe that the apparent discrepan- cies in the orbits of Uranus and Neptune were due to observational error in the older data.

RC Winther


Is there really a planet X? The real question is what kind of measurements could you design to see if there is one. One could be the amount of gravity pull that would be present if there were a planet on the opposite side of the Sun. Could it be detectable? There have been probes that have gone out far from the Earth and what kind of camera would we need for them to detect? A big effect should be felt on certain comets and I do not think that anyone saw anything strange about recent comets. The effect on their orbit should be observable. None of these kind of effects have been observed and on that basis most would conclude that this idea has no merit. Can you think of an experiment that would show its presence?

Is there any new evidence to this theory? Steve, your question is a good one. I have seen no evidence that is convincing that there is a 10th planet. Even is there was it would probably be very small and not very interesting. While people have been looking I do not feel any one has convincing evidence. Most people are looking for things like dark matter and black holes to see if the universe is open or closed.

Samuel P Bowen


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