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Hi Dean,
Steffen and Jacquie have answered better than I could. And yes, it seems astonishing that we have such a poor grasp of the orbit of Pluto, and such a poor knowledge of the position of the occulted star.
But that is the current state of play.
When Gaia finishes its observing run an a couple of years, our astrometry will be ten times more precise than what we have now.
Also you may consider that Pluto has (as far as I know) the best determined orbit of any of the objects beyond Neptune. At least the uncertaintly is only about one planetary diameter. So there is still an awful lot of work to do even in the solar system to refine our knowledge, and this is work that amateurs can play a pivotal role in. Occultations of trans-Neptunian objects benefit greatly from amateur involvement. We may not have the biggest scopes or the coolest cameras, but there are enough of us to spread out widely and refine these orbits in a way that the professional astronomers cannot do.
As far as the info from New Horizons being able to refine our knowledge of the position of Pluto ... the uncertainties in all spacecraft motions require "mid-course corrections" at points along the way. So New Horizons' position is being refined as it gets closer to its target, which is good. Unfortunately, the occulted star's position is still not as well known. Astrometry is probably the biggest source of error, with the Pluto orbit being second. The post from MIT mentioned above has astrometry on the target star to about 29 milli-arc-sec, which is pretty good, but all the errors could push the path north or south by more than 1000 km (1 standard deviation of the error = 1097km).
The bottom line - observe first, and settle the question with direct measurements.
Regards,
Tony Barry
WSAAG
Last edited by tonybarry; 31-05-2015 at 10:52 AM.
Reason: added bit about New Horizons refining orbit
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