In article ,
Bruce Sterling Woodcock wrote:
And Pluto is 57.5 degrees retrograde? The latter is new to me as I had
not known that we knew the axis tilt of Pluto.

We determined it once we had radar pictures (and the Hubble).

No, what quickly settled Pluto's axial tilt was the discovery of Charon
(Pluto's moon) in the early 1980s. With a moon that big and close, the
two just had to be tide-locked together, so the easily-observable orbit
of Charon also gave us Pluto's axis.
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MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |