From: utzoo!decvax!cca!Lynn.ES@PARC-MAXC@sri-unix
Newsgroups: net.space
Title: Re: Space Search (V2 #225)
Article-I.D.: sri-unix.1937
Posted: Mon Jun 28 12:18:58 1982
Received: Tue Jun 29 06:21:05 1982

Some of the possibilities to explain outer planet perturbations are very
speculative, to say the least.  Tombaugh (discoverer of Pluto) and other
astronomers knew in the 30's that Pluto was too small to explain the
perturbations, if the estimated accuracies of positions for Uranus and Neptune
were correct.  That is why Tombaugh continued his search of all parts of the sky
except the polar regions for more than an additional decade.  He pretty well ruled
out the possibility of a planet with any reasonable brightness within a reasonable
distance of the sun (several times Pluto's distance).  

The alternative, of course, is that the accuracy of positional measurements of
Uranus and Neptune was just not that good.  Both the discoveries of Neptune
and Pluto near the places predicted by perturbation analysis have been called
lucky coincidences, since the perturbations being analyzed were nearly
indistinguishable from errors in positional measurement.  The orbits and masses
of the predicted planets didn't agree very well, only the positions at discovery
time did.  

One thing that has sparked new hope for another planet/object is the discovery
in Galileo's notes of his sighting of an object that has to be Neptune.  The
position is somewhat off from predictions, but again is of questionable accuracy. 
The newly derived mass of Pluto from measurements of its satellite was claimed
to have prompted excitement, but even its old erroneously large mass estimate
was far too small to explain the perturbations.  

Jupiter has been called a near-star that never ignited, so I am not sure there is
any difference between a large planet and a "brown dwarf".  Anyway, don't
hold your breath till an object is found.  I think the odds are against it, but that
does not mean we should not analyze the Pioneer spacecraft data for
perturbations.  It just might lay to rest the speculations on another planet.  Then
there is always a chance ...

/Don Lynn