Quote:
Originally Posted by grant hutchison
But I agree that in general we don't need to watch an entire orbit to compute its characteristics: just a long enough segment to allow the rest to be calculated with useful confidence. However, I think Kullat Nunu is suggesting that to be sure the observed pattern in the data is an orbit, we probably need to observe at least one cycle.
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I'm no expert, but that's what the exoplanet hunters have told. Considering how much distant orbits change when new data points are acquired, a very incomplete orbit probably gives highly unrealistic values. Take for example 55 Cnc d, the outermost planet in the system. It was originally believed to be in a highly eccentric orbit. Now its eccentricity seems to be mere 0.025. Similarly, some of the distant planets have wildly varying values (compare the values of HD 154345 at the
Extrasolar Planets Encyclopaedia and the
Catalog of Extrasolar Planets. The former suggests a more distant and much more eccentric orbit (9.21 AU, 0.474) compared to the latter more up-to-date values (4.17 AU, 0.050; a very Jupiter-like planet).